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Tambora 1815 as a test case for high impact volcanic eruptions: Earth system effects: Tambora 1815 as a test case for high impact volcanic eruptions

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The eruption of Tambora (Indonesia) in April 1815 had substantial effects on global climate and led to the ‘Year Without a Summer’ of 1816 in Europe and North America. Although a tragic event—tens of thousands of people lost their lives—the eruption also was an ‘experiment of nature’ from which science has learned until today. The aim of this study is to summarize our current understanding of the Tambora eruption and its effects on climate as expressed in early instrumental observations, climate proxies and geological evidence, climate reconstructions, and model simulations. Progress has been made with respect to our understanding of the eruption process and estimated amount of SO2 injected into the atmosphere, although large uncertainties still exist with respect to altitude and hemispheric distribution of Tambora aerosols. With respect to climate effects, the global and Northern Hemispheric cooling are well constrained by proxies whereas there is no strong signal in Southern Hemisphere proxies. Newly recovered early instrumental information for Western Europe and parts of North America, regions with particularly strong climate effects, allow Tambora's effect on the weather systems to be addressed. Climate models respond to prescribed Tambora-like forcing with a strengthening of the wintertime stratospheric polar vortex, global cooling and a slowdown of the water cycle, weakening of the summer monsoon circulations, a strengthening of the Atlantic Meridional Overturning Circulation, and a decrease of atmospheric CO2. Combining observations, climate proxies, and model simulations for the case of Tambora, a better understanding of climate processes has emerged. WIREs Clim Change 2016, 7:569–589. doi: 10.1002/wcc.407. For further resources related to this article, please visit the WIREs website. © 2016 The Authors. WIREs Climate Change published by Wiley Periodicals, Inc.
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Tambora 1815 as a test case for
high impact volcanic eruptions:
Earth system effects
Christoph C. Raible,
1,2
Stefan Brönnimann,
1,3
*Renate Auchmann,
1,3
Philip Brohan,
4
Thomas L. Frölicher,
5
Hans-F. Graf,
6
Phil Jones,
7,8
Jürg Luterbacher,
9,14
Stefan Muthers,
1,2
Raphael Neukom,
1,3
Alan Robock,
10
Stephen Self,
11
Adjat Sudrajat,
12
Claudia Timmreck
13
and Martin Wegmann
1,3
Edited by Matilde Rusticucci, Domain Editor, and Mike Hulme, Editor-in-Chief.
The eruption of Tambora (Indonesia) in April 1815 had substantial effects on
global climate and led to the Year Without a Summerof 1816 in Europe and
North America. Although a tragic eventtens of thousands of people lost their
livesthe eruption also was an experiment of naturefrom which science has
learned until today. The aim of this study is to summarize our current under-
standing of the Tambora eruption and its effects on climate as expressed in
early instrumental observations, climate proxies and geological evidence, cli-
mate reconstructions, and model simulations. Progress has been made with
respect to our understanding of the eruption process and estimated amount of
SO
2
injected into the atmosphere, although large uncertainties still exist with
respect to altitude and hemispheric distribution of Tambora aerosols. With
respect to climate effects, the global and Northern Hemispheric cooling are well
constrained by proxies whereas there is no strong signal in Southern Hemi-
sphere proxies. Newly recovered early instrumental information for Western
Europe and parts of North America, regions with particularly strong climate
effects, allow Tamboras effect on the weather systems to be addressed. Climate
models respond to prescribed Tambora-like forcing with a strengthening of the
wintertime stratospheric polar vortex, global cooling and a slowdown of the
These authors contributed equally.
*Correspondence to: stefan.broennimann@giub.unibe.ch
1
Oeschger Centre for Climate Change Research, University of
Bern, Bern, Switzerland
2
Climate and Environmental Physics, University of Bern, Bern,
Switzerland
3
Institute of Geography, University of Bern, Bern, Switzerland
4
Met Ofce Hadley Centre, Exeter, UK
5
Environmental Physics, Institute of Biogeochemistry and Pollutant
Dynamics, ETH Zürich, Zürich, Switzerland
6
Geography Department, Centre for Atmospheric Science, Univer-
sity of Cambridge, Cambridge, UK
7
Climatic Research Unit, University of East Anglia, Norwich, UK
8
Department of Meteorology, Center of Excellence for Climate
Change Research, King Abdulaziz University, Jeddah, Saudi Arabia
9
Department of Geography, Climatology Climate Dynamics and
Climate Change, Justus Liebig University of Giessen, Giessen,
Germany
10
Department of Environmental Sciences, Rutgers University, New
Brunswick, NJ, USA
11
Department of Earth and Planetary Science, University of
California, Berkeley, CA, USA
12
Department of Geology, Padjadjaran University, Bandung,
Indonesia
13
Max Planck-Institute for Meteorology, Hamburg, Germany
14
Centre for International Development and Environmental
Research, Justus Liebig University Giessen, Giessen, Germany
Conict of interest: The authors have declared no conicts of inter-
est for this article.
© 2016 The Authors.
WIREs Climate Change
published by Wiley Periodicals, Inc.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in
any medium, provided the original work is properly cited, the use is non-commercial and no modications or adaptations are made.
water cycle, weakening of the summer monsoon circulations, a strengthening
of the Atlantic Meridional Overturning Circulation, and a decrease of atmos-
pheric CO
2
. Combining observations, climate proxies, and model simulations
for the case of Tambora, a better understanding of climate processes has
emerged. © 2016 The Authors. WIREs Climate Change published by Wiley Periodicals, Inc.
How to cite this article:
WIREs Clim Change 2016. doi: 10.1002/wcc.407
INTRODUCTION
In April 1815, the dormant volcano Tambora on
the Indonesian island of Sumbawa (8.25S,
118.00E; Figure 1) erupted violently. The eruption
immediately killed thousands of people on Sumbawa.
During the following months, tens of thousands died
of starvation and disease on Sumbawa and neighbor-
ing islands. The gas plume of this enormous eruption,
the largest since the 1257 Samalas eruption (shown
as Rinjani in Figure 1), produced stratospheric
sulfate aerosols that shielded incoming solar radiation
over the following 3 years.
1
The aerosols led to a sub-
stantial annual cooling of the Tropics and the extra-
tropical Northern Hemisphere by approximately
0.40.8C relative to the preceding 30 years.
24
The
following year, 1816, went down in history as a
Year without a Summer,
57
resulting in large socio-
economic impacts such as crop failures and associ-
ated famines, across the Northern Hemisphere,
including China, North America, and Europe.
811
Given these worldwide impacts, the Tambora erup-
tion must be considered to have had one of the great-
est death tolls attributed to a volcanic eruption.
The Tambora eruption and its climatic conse-
quences were studied repeatedly over the past century
with respect to diverse research questions ranging
from ice age theory,
12
asteroid impacts, nuclear
winter, and others.
13
Arst comprehensive overview
of the Tambora effects was published in 1992. The
book by Harington
7
compiled the ndings with
respect to imprints in proxies, climate data, and soci-
etal impacts across various disciplines, constituting
an authoritative reference on Tambora impacts.
However, much has been learned since the publica-
tion of Harington (1992) using new palaeoclimatolo-
gical evidence from different archives, newly digitized
instrumental data and documentary evidence, and
particularly using coupled climate models. The bicen-
tenary of the Tambora eruption provides an opportu-
nity to revisit the event and revisit our understanding
of its effects on climate.
As an experiment of nature,
14
the Tambora
eruption allows current scientists to test hypotheses
on the interaction between the solid Earth and the
atmosphere, atmospheric chemistry and physics,
dynamics and radiation, stratosphere and tropo-
sphere, atmosphere and oceans, climate and bio-
sphere, climate and society, and many others.
Because of its magnitude and its severe impacts,
Tambora may provide additional insights to those
obtained from studying more recent, better observed
eruptions. These new insights contribute to better
process understanding, help to project the possible
consequences of future eruptions, and may be
50 km
Sumbawa
Sanggar
Peninsula
Moyo
Lombok
Tambora
Samalas caldera
(Rinjani)
FIGURE 1 |Map of the LombokSumbawa sector of the Sunda arc, Indonesia, showing the location of Tambora and Rinjani, the sites of the
probably two largest eruptions of the last millennium. The map was generated using GeoMapApp©. (Reprinted with permission from Ref 145.
Copyright 2015 John Wiley and Sons)
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relevant for assessing geoengineering options. In par-
ticular, Tambora is a good test case for studying his-
torical climate-society interactions. Tambora erupted
at the beginning of the early instrumental period so
that making best use of observations, proxy informa-
tion, reconstructions, model simulations, and histori-
cal evidence is essential and thus calls for a
multidisciplinary approach. This paper focuses on
the physical processes.
The paper rst provides an overview of the
eruption, stratospheric aerosols, and radiative forcing
(second section). This section is based on volcanolog-
ical evidence on the eruption and eyewitness
accounts, but also evidence from environmental
archives such as sulfate from polar ice cores. The
analysis includes comparisons with well-observed
eruptions including Pinatubo (1991), as well as com-
puter model results. The third section focuses on
early instrumental data and derived summer tempera-
ture, precipitation, and sea-level pressure reconstruc-
tions for the North Atlantic and Europe for which
the most abundant information is available. The Fol-
lowing section then analyzes the climatic imprint of
the Tambora eruption in various natural archives
such as tree rings, ice cores, or sediments. The fth
section summarizes climate model studies of the
Tambora eruption and large volcanic eruptions in
general, as models are an important tool to address
the underlying mechanisms. Finally, we present con-
clusions and summarize from a present day perspec-
tive what we can learn from the Tambora event.
THE TAMBORA ERUPTION,
AEROSOLS, AND RADIATIVE FORCING
Tambora is a massive, shield-like volcano that occu-
pies much of the Sanggar Peninsula in northern Sum-
bawa, part of the Lesser Sunda Islands in Indonesia
(Figure 1). The volcano reaches a height of 2850 m,
but before 1815, it may have been one of Indonesias
highest mountains, more than 4000 m in elevation.
15
The climactic phase of the eruption on April
1011, 1815,
1,16
which followed almost a week of
minor and intermittent explosions, caused the sum-
mit to collapse, forming a caldera 6 ×7 km wide
and more than 1 km deep (Figure 2).
The 1815 Tambora eruption is probably the
largest caldera-forming eruption of the last few cen-
turies. Recent estimates suggest an erupted magma
(dense rock equivalent; DRE) volume of
~3050 km
3
.
1,17
It is thought that this magma was a
relatively homogeneous trachyandesite that was
stored in a shallow crustal reservoir before the erup-
tion. During the eruption, pyroclastic ows swept
down all anks of the volcano and into the sea
extending the coastline of the Sanggar Peninsula. The
pyroclastic ows and related phenomena were
mainly responsible for the casualties on Sumbawa
Island. Pumice and coarse ash fell close to the vol-
cano on the Sanggar Peninsula, but according to eye-
witness accounts the nest volcanic ash fell as far as
western Java, at least 1300 km from the source, and
much was deposited into the sea. Remobilization of
the volcanic deposits on land, and the fact that a sig-
nicant portion of the 1815 ejecta owed or fell into
the sea, make an accurate determination of the erup-
tion volume difcult. For some, if not most of the
older large Holocene eruptions, some of which were
likely to be signicantly larger than Tambora, the
erupted volumes reported may be even less accurate.
On the basis of the above uncertainties, the
measured sulfur content of both the pre-eruption vol-
atile content (from measurements on inclusions in
crystals in the 1815 tephra deposit) and degassed
magma (from measurements on volcanic glass in the
deposit) gives an emitted SO
2
mass of about 60 Mt
(Tg) at the low end of the range of volumes,
18
or lar-
ger if the true volume is shown to be bigger.
The stratigraphy of tephra deposits explored
about 25 km from the Tambora summit sheds some
FIGURE 2 |The 7 ×6 km wide and more than 1-km deep summit caldera of Tambora created by the 1815 eruption. The 1815 eruptive
products form the top of the caldera wall, as seen in the foreground. On the oor of the caldera lie an ephemeral lake and a small cone from a
post-1815 eruption. Photo by Katie Preece. (Reprinted with permission from Ref 145. Copyright 2015 John Wiley and Sons)
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light on the sequence of eruption phases.
16
Prior to
the cataclysmic eruption on April 10, 1815, a series
of less intense phreatomagmatic and Plinian erup-
tions took place with maximum intensity of the erup-
tion exceeding 10
8
kg s
1
, leading to maximum
plume heights of more than 30 km. The eruption cul-
minated in the climactic eruption of April 1011 with
an intensity of probably 3 ×10
8
kg s
1
and a maxi-
mum plume height of more than 40 km.
16
However,
this arguably reects overshoot heights rather than
the altitude at which the bulk of the gases was
injected.
19
The huge Plinian eruption column col-
lapsed and formed giant pyroclastic ows from
which the main co-ignimbrite or Phoenix plume
arose. This sequence of events is essential for the
atmospheric injection height of SO
2
and ne ash.
Observations after more recent big eruptions and
model simulations
20
show that the vertical proles of
SO
2
and ne ash injection have maxima near the
neutral buoyancy height (NBH), which is signi-
cantly lower than the maximum plume height. Dur-
ing Plinian phases, when the convection of the plume
is well organized, initial momentum and heat propel
ne ash and gases to heights above the NBH, but
most of the material will fall back to the NBH, forc-
ing a spread of the plumed umbrella that can exceed
100 m s
1
, leading to very fast horizontal transport
of ash at NBH and distant ash fall afterwards. If the
mass load within the plume becomes too high, the
plume starts collapsing and feeds pyroclastic ows
rapidly surging down the anks of the volcano for
tens of kilometers and lling the near-surface atmos-
phere with a mixture of hot gases and ash.
From this hot pillow,very ne ash particles
and gases will be elutriated and form another, sec-
ondary eruption column, the Phoenix or co-
ignimbrite cloud. Owing to the spatial extent of this
Phoenix cloud, convection is less organized and the
NBH is lower than for the original Plinian plume.
Merger of both will lead to hybrid plumes. The
plume dynamics depend on a wide range of in-plume
processes such as condensation and freezing of water
with formation of hydrometeors and latent heat
release, aggregation of ash particles, rainout, wash-
out and freeze-out of gases and particles, electric
charging, of which, for historic eruptions, we are
mostly lacking observed information. Such events
were simulated for eruptions close to the Tambora
eruption rates.
21
For mass eruption rates of
1.3 ×10
8
kg s
1
van Eaton et al.
21
found NBH
based on maximum ash concentration of about
13 km for dry co-ignimbrite plumes and around
22 km for Plinian columns with initial water content
of 10%. For mass eruption rates of 1.1 ×10
9
kg s
1
,
they found NBH based on maximum ash concentra-
tion of about 18 km for dry co-ignimbrite plumes
and around 23 km for Plinian columns. Maximum
eruption heights for these cases were simulated to
about 3242 km, that is, much higher than the NBH.
Gas injection heights are generally slightly higher
than ash injection heights. For the Tambora mass
eruption rates, we can therefore assume a vertical
prole with a maximum injection of SO
2
between
20 and 25 km. This corresponds well with observed
injection height proles after the smaller 1991 Pina-
tubo eruption.
The sulfate aerosol cloud that developed from
the injected SO
2
was spread globally by the strato-
spheric winds. The stratospheric meridional circula-
tion transported the aerosols poleward. Ultimately,
the sulfate reached the troposphere, where it was
quickly washed out. Today, Tamboras sulfate signal
is still preserved in polar ice cores. In fact, estimates
of sulfate mass uxes from bipolar ice cores provide
the basis for reconstructing stratospheric sulfur
amounts and of radiative forcing. However, this
requires an assumption on the efciencies of strato-
spheric transport in each hemisphere. While Gao
et al.
22
found an approximately equal distribution of
sulfate deposition in Antarctic and Greenland ice
cores, Sigl et al.
23
suggested considerably higher sul-
fate uxes in Antarctica as compared to Greenland.
This appears inconsistent with the fact that climate
effects were arguably much stronger in the Northern
Hemisphere than the Southern Hemisphere (Proxies
and Proxy-Based Reconstructions section). In a two-
dimensional aerosol model study using a sulfate
injection rate determined from ice cores, Arfeuille
et al.
19
found a strongly asymmetric distribution of
hemispheric aerosol loading after the Tambora erup-
tion. Owing to the timing of the Tambora eruption,
at the start of the Southern Hemisphere winter sea-
son, they found that the majority of the aerosol load
was transported southward, albeit stratospheric cir-
culation in 1815 is of course unknown and was pre-
scribed in the model based on more recent data. The
hemispheric partitioning of aerosols thus remains an
open question. Greenland and Antarctic deposition
efciencies (the ratio of sulfate ux to each ice sheet
to the maximum hemispheric stratospheric sulfate
aerosol burden) vary as a function of the magnitude
and season of stratospheric sulfur injection.
24
Based on ice core-based estimates, the Tambora
SO
2
injection was about 3.5 times larger than the
1991 Pinatubo eruption, but the resulting radiative
forcing was only about two times higher, assuming
that the larger SO
2
injection produced larger aerosol
particles, with resulting smaller lifetimes and less
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impact on radiation per unit mass.
19,25
The peak net
radiative forcing from Tambora was about
5Wm
2
(dened as global downward short-wave
radiative forcing at the tropopause
25
or global top-
of-atmosphere downward net radiation anoma-
lies
26,27
). The climate response to this thick aerosol
cloud is discussed in the following sections.
CLIMATE RESPONSE
IN OBSERVATIONS
Widespread meteorological observations across much
of Western and Central Europe began in the
1780s.
28
Longer series have been developed at the
monthly timescale for a number of locations extend-
ing back to the 17th century.
2932
More recent work
has seen this development extended to the daily
timescale
3337
ranging from Iberia in the west to
European Russia in the east. By the 18th century,
efforts to develop distinct meteorological networks
had emerged due to the urgings and coordination of
the Royal Society in England (by the Societys Secre-
tary James Jurin), from the medical fraternity in
France (by the Societe Royale de Medecine
17761789), in Bavaria (by the Bavarian Academy
of Science 17811789, in the Bayerische Ephemeri-
den) and across Europe (under the Societas Meteoro-
logica Palatina in Mannheim, 17811792), even
enabling weather maps to be drawn for this dec-
ade.
38
The Mannheim Ephemerides, reporting subda-
ily meteorological observations from a network of up
to 50 stations, ended in 1792 due to the Napoleonic
Wars, and the availability of material for the 1800s
and 1810s is somewhat less extensive than the two
earlier decades and since the 1820s. Briffa and
Jones
39
presented temperature anomaly maps for the
four seasons during 1816 and for the 1810s
(18101819) with respect to 19511970 for tempera-
ture and 19211960 for precipitation. These were
based on 46 temperature and 29 precipitation series.
The precipitation series were restricted to Poland
westwards, but temperature data were available at
Archangel, Vilnius, St Petersburg, Kiev and Kazan
east of Poland. In Figure 3, we update these results
using more recently produced series from Europe and
extend the independently reconstructed sea-level
pressure, temperature, and precipitation maps
32,40
to
encompass more areas of the North-
Atlantic-European region than available in 1992.
Atmospheric circulation in the summer of 1816
was characterized by a weak Azores high and a
strong Icelandic low (Figure 3, top). Sea-level pressure
reconstructions based on land station pressure series
and information from ship log books from the eastern
North Atlantic
40
reveal below normal pressure over
the North Atlantic European region (30W40E
and 3070N) connected with more frequent low-
Sea-level pressure (hPa)
70N
60N
50N
40N
30N
70N
60N
50N
40N
30N
70N
60N
50N
40N
30N
Precipitation (%)
–2.5
–2
–1.5
–1
–0.5
0
0.5
220
200
180
160
140
120
100
80
60
40
1
1. 5
2
2.5
–6
–4
–2
0
2
30W 20W 10W 0 10E 20E 30E 40E
30W 20W 10W 0 10E 20E 30E 40E
30W 20W 10W 010E
20E 30E 40E
Temperature (K)
FIGURE 3 |(Top): Sea-level pressure (contour lines, in hPa) and
anomalies (stippled lines; in hPa) for summer (June-August) 1816
statistically reconstructed using station pressure series in combination
with ship log book information from the northeastern North Atlantic
(data from Küttel et al.
40
). (Middle): temperature anomalies (in C) for
summer 1816 statistically reconstructed using station temperature
series only (data from Casty et al.
32
). (Bottom): precipitation (in % of
the 19611990 average) for summer 1816 statistically reconstructed
using station precipitation series only (data from Casty et al.
32
).
Temperature and precipitation reconstructions in the outer margins of
Europe and the Mediterranean are less certain due to the lack of
meteorological station information for those areas. All anomalies are
with respect to 19611990.
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pressure systems and generally a stronger westerly
and northwesterly air ow toward Europe.
For temperature (Figure 3, middle), the most
anomalous cold summer temperatures were centered
on Switzerland and eastern France. The summer of
1816 was one of the coldest summers measured over
much of Western Europe from Central Scandinavia to
the Mediterranean. Further east the few series in
Russia and the Ukraine indicate a milder summer in
1816. This might be due to more southerly atmos-
pheric ow from Northern Africa through Turkey to
western Russia (Figure 3, top). Anomalous low pres-
sure over large parts of the North Atlantic and
Europe (Figure 3, top) was connected with excessive
rainfall across most of Western Europe, north of the
Mediterranean. Particularly in southeast England and
northeastern France (Figure 3, bottom), this summer
was most anomalously wet. European instrumental
averages indicate that the 1810s were the coldest dec-
ade since comparable records began in the 1780s.
Most years within the 1810s would be classed as cold
(relative to 19611990), but 2 years, 1814 and 1816
stand out as being exceptionally cold. Part of this was
probably due to the unknown eruption in 1808/
1809
41
that is clearly evident in ice core series.
23
The year without a summer of 1816 has also
been extensively studied in these single site records
(see papers in Harington
7
). More recent work has
used series where the subdaily data have now been
digitized.
42,43
The analysis of twice-daily data from
Geneva,
42
which is located in the region with the lar-
gest negative temperature anomaly in 1816 in Europe
(see Pster,
44
Trigo et al.,
45
and Figure 3), shows that
the afternoon temperature anomalies (compared to
the contemporary reference period 17991821, with-
out the volcanically perturbed years 18091811 and
18151817) were more strongly affected than the
morning temperatures. The entire distribution of tem-
perature anomalies was shifted by 3.8C compared
to the reference period. For the sunrise temperature,
a smaller shift (-1.8C) was found, with a distinct
narrowing of the distribution. Extremely low sunrise
temperatures were as rare in 1816 as in the reference
period, but warmer than average sunrise tempera-
tures were missing.
42
Both the larger change in after-
noon temperatures and the change in the distribution
can be explained by an increase in cloud cover,
which is well documented and can in turn be related
to a signicant change in weather types. For Geneva,
a tripling of low pressuresituations and an absence
of high pressuresituations was observed as illus-
trated by the pressure reconstruction in Figure 3. Pre-
cipitation in Geneva in summer 1816 increased by
80% but with no change in the intensity distribution,
that is, the frequency of precipitation days
increased.
42
Analysis of this single site suggests that
the summer 1816 was characterized by extreme cli-
mate (weather types statistics) and not extreme
weather (the tails of the distributions were not much
affected). Subdaily pressure data from around 50 sites
in Europe and North America show an increased syn-
optic activity (measured by a 26 days bandpass lter
and expressed relative to a present day climatology)
in a band stretching from western France to Austria.
This suggests increased storminess due to frequent
passages of storms, consistent with the space-time
pattern of precipitation.
43
These anomalies in weather
patterns found in the observations are qualitatively
consistent with model studies (see Section MODEL-
ING THE CLIMATE EFFECT OF THE TAMBORA
ERUPTION), although presumably a large fraction of
unforced variability contributed.
Other long daily series across Europe have also
been analyzed. The most well-known temperature
series is the Central England Temperature (CET)
series, which extends back on a monthly timescale to
1659 and to 1772 at the daily timescale.
46
Focusing
just on the JJA summer, 1816 stands out as the cold-
est summer of the 1810s and in the long CET series as
the third coldest summer since 1659 (colder summers
were measured in 1725 and 1695). Figure 4 shows
the daily temperatures during 1816 compared to
those in the most recent complete year (2014) which
was the warmest year in the CET series. For 1816
only a few days were above the 196190 period, with
only 1 week in the spring and summer (in late April)
being above. 2014, in contrast, experienced only a
few days below average. Averaged annually, the
2 years differ by only 3.0C, with 1816 having an
average of 7.9C and 2014 an average of 10.9C.
Whilst much of Europe was exceedingly cold
and wet during the summer of 1816 (in agreement
with the consistent lower than average pressures,
Figure 3 top), the entire North Atlantic European
region (shown in Figure 3, land-only) was much closer
to average (see also Figure 3). Temperatures were
average in the far north of Sweden
47,48
and above
normal at St Petersburg.
49
Further aeld, the summer
was known to be very cold in New England (3.0C
below the 19611990 average at Boston,
7
where it is
referred to as the Year Without a Summer). Recent
model-constrained reconstructions indicate that over
a large part of eastern North America, temperatures
were 2C below the 17001890 average.
50
Estimates of the temperature impacts of Tam-
bora over a wider spatial scale are available from
marine observations.
51
The English East India Com-
pany maintained a eet of ships trading between
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Britain and southeastern Asia over a long period, and
between about 1794 and 1833 many of these ships
recorded noon temperatures in their logs. These obser-
vations allow annual temperature variability to be
reconstructed over a large area of the Atlantic and
Indian Oceans.
52
The year 1816 was the coldest year
over this region, for this period, with an anomaly of
about 0.6C compared to the 17941833 period aver-
age (the second coldest year was 1809, also volcani-
cally inuenced by the unknown 1808/1809 eruption).
Shipslogs also provide climate information
from other regions. The Hudsons Bay Company
ships traveled between Britain and trading posts in
Hudsons Bay in present-day Canada. These ships did
not record instrumental weather observations, but
their logs do provide rich information on the sea-ice
conditions in Hudson Strait over the period
17511870. Sea-ice conditions were more severe in
1816 than in any other year in this record.
53
How-
ever, these extreme ice conditions are arguably more
likely to be a result of anomalous local circulation
than of large-scale temperature changes
54
this is
illustrated by the contrasting observations of William
Scoresby Jr
55
: Scoresby recorded temperatures on
whaling voyages in the Greenland Sea every summer
from 1810 to 1818 and these observations indicate
that 1816 was a relatively warm year, with less than
the usual sea-ice coverage.
56
Scoresby emphasized this
in a letter to Sir Joseph Banks, president of the Royal
Society, stating: I observed on my last voyage (1817)
about 2000 square leagues [18 000 square miles] of
the surface of the Greenland seas, included between
the parallels of 74and 80, perfectly void of ice, all
of which disappeared within the last two years.
57
The instrumental observations clearly show the
expected moderate large-scale cooling effect of the
eruption, but also demonstrate that local effects can
be quite different from the large-scale mean, and
sometimes much more extreme. However, for much
of the world in 1816, no instrumental observation
records are currently available, so we must turn to
proxy data to see what happened in those regions.
CLIMATE IMPRINT IN PROXIES AND
PROXY-BASED RECONSTRUCTIONS
Apart from instrumental information, natural
sources can provide further information on the sum-
mer temperature and precipitation conditions in
1816. From statistically reconstructed global or
Northern Hemispheric annual mean temperature
reconstructions,
24,58,59
it becomes obvious that
1816 was among the coldest years of the past centu-
ries. However, the various published reconstructions
disagree about the amplitude of the anomaly.
60
Com-
pared to the 19611990 period, estimates range from
0.66 0.24C (standard deviation) for Northern
Hemisphere temperature,
59
to 1.14C for the tem-
perature between 30and 90N
2
and 1.9C for the
Northern Hemisphere
61
(differences relative to
17851815 are much smaller, in the range of 0.4 to
0.8C). It is important that in most reconstructions,
the summer of 1816 followed a period with a nega-
tive temperature trend. The early 1810s were possi-
bly already being inuenced by the volcano in 1808/
1809 and the lower solar insolation during the Dal-
ton Minimum (17901830).
April
Januar y
–15
–10 Daily Central England Temperature (Parker & Horton 2005)
1961–1990 smoothed normals
1961–1990 smoothed 5th & 95th percentiles
Daily Central England Temperature (Parker & Horton 2005)
1961–1990 smoothed normals
1961–1990 smoothed 5th & 95th percentiles
–5
0
5
10
Temperature (°C)
15
20
25
–5
–10
0
5
10
15
Temperature (°C)
20
25
30
1816
2014
July
October
Januar y
April
Januar y
July
October
Januar y
FIGURE 4 |Daily Central England temperatures for each day of
the year for 1816 and 2014. Absolute temperatures are shown in blue
and these can be compared with average values based on the
19611990 period. Apart from averages, the panels for the 2 years
also show a number of percentile ranges (5/95) to illustrate how
unusual some days are with respect to the distribution of individual
days based on the 19611990 period.
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Most natural proxies (e.g., trees, lake/marine
varves) and historical records
62,63
tell us about condi-
tions in the summer, and it is this season that had the
largest impact in 1816 across Europe and eastern
North America. Information from tree rings provides
indications about mean summer climate across the
boreal forest zones of North America and Eurasia.
Tree ring density is currently the most accurate proxy
for the interannual temperature response to volcanic
eruptions.
64
Using tree ring density data, Briffa
et al.
65
showed positive temperature anomalies over
parts of western America, but cold and very cold
conditions around the rest of the mid latitudes of the
Northern Hemisphere. This is in agreement with
other tree ring-based summer temperature recon-
structions that indicate strong summer cooling in
1816 in large parts of the Arctic, Northern Europe,
eastern North America, and Asia.
6668
This change
in the pattern of anomalies suggests a different
Rossby-wave pattern during this summer than expe-
rienced in most summers during the last 200 years.
For the winter 1816/1817, climate eld recon-
structions suggest a winter warming
32
similar to the
temperature pattern found in composite analysis of
strong volcanic eruptions during the last 500 years.
69
The reason for this warming is the North Atlantic
Oscillation (NAO) which develops a positive phase
after a volcanic eruption, that is, enhanced westerlies
over the Atlantic European region. This dynamical
response is conrmed by a recent NAO reconstruc-
tion showing a positive phase of the NAO in the win-
ter 1816/1817.
69
While the proxies from the Northern Hemi-
sphere land areas generally show substantial cooling
in 1816, Tamboras temperature imprint in the
Southern Hemisphere appears to be substantially
weaker. Hemispheric temperatures
70
do not show a
signicant cooling in the years following the erup-
tion, neither do regional reconstructions from South
America, Australasia, and Antarctica.
71
This weak
response is generally consistent for large volcanic
eruptions over the past centuries. As the Southern
Hemisphere is mostly covered by oceans and its land
masses are distributed more toward lower latitudes
than their northern counterparts, a weaker and less
immediate climatic response to volcanic eruptions is
expected. Modes of internal variability, particularly
of El Niño/Southern Oscillation (ENSO) and the
Southern Annular Mode (SAM) have a very strong
inuence on the Southern Hemisphere continents.
Reconstructions of the SAM
72
do not indicate a sig-
nicant response to volcanic eruptions. A shift of
ENSO toward an El-Niño state is found in some
studies.
73
However, it does not stand out of internal
variability, which is generally larger than externally
forced inuences.
74
This nonresponse in key circula-
tion modes may explain the weak imprint of volcanic
eruptions on continental temperatures in the South-
ern Hemisphere. These ndings from the Southern
Hemisphere are not in agreement with many climate
models, which usually nd volcanic cooling of simi-
lar amplitude in both hemispheres.
70
Thus, current
climate models tend to overemphasize interhemi-
spheric synchronicity by underestimating the inu-
ence of internal variability particularly in the
Southern Hemisphere.
70
However, the temporal and
spatial proxy data coverage is still much weaker in
the Southern Hemisphere compared to Europe and
North America. Hence, the apparent absence of vol-
canic cooling in the Southern Hemisphere may be an
artifact of the low number of records able to resolve
short-term peaks of climatic anomalies. Alternatively
(though not supported by ice cores), the amount of
aerosols reaching the Southern Hemisphere might
have been smaller than assumed in these models.
Recent coral-based reconstructions of tropical
SSTs in the Indian, West and East Pacic Oceans
show the coldest temperatures over the past
400 years in the early 19th century.
74
While only the
Indian Ocean displays a distinct interannual cold
anomaly after the Tambora eruption, the decadal-
scale cooling starts around 1800 in all three basins,
indicating that Tambora amplies, rather than trig-
gers the cold period. However, the level of this ampli-
cation via volcanic eruptions cannot be quantied
with reconstructions alone.
Drought reconstructions have been produced
based on tree ring information from North America
and for South Asia.
75,76
The Monsoon Asia Drought
Atlas for MaySeptember 1816 shows dry conditions
in India and South Eastern Asia (weakening of the
monsoon) and anomalous wet conditions in northern
parts of Asia.
76
This is partly consistent with multi-
proxy (tree rings, historical documentary records,
and ice cores) MaySeptember precipitation recon-
structions by Feng et al.
77
The North America
Drought Atlas for 1816 indicates wet conditions in
the US Southwest (though mainly a winter response)
and summer drought in the East.
75
MODELING THE CLIMATE EFFECT
OF THE TAMBORA ERUPTION
Climate models are an important tool to study the
mechanisms of Tamboras impact on climate.
7882
In
fact, model results for the Tambora eruption agree
with sparse observations and proxy data in some
aspects.
7881
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understanding of the mechanisms, results need to be
reconciled with those found for other strong tropical
volcanic eruptions. In agreement with observations
and reconstructions, climate modeling studies show a
drop in near-surface temperature of about 1C over
the global land areas after the Tambora eruption
(Tables 1 and 2). The temperature minimum lags
behind the aerosol optical depth maximum by about
2 years and gradually returns to climatological mean
values after 610 years (Figure 5 for Northern Hemi-
sphere temperatures). The ocean cools less than the
land due to its greater heat capacity. As a result of
reduced near-surface temperatures, simulated North-
ern hemispheric sea ice is increased and peaks
37 years after the eruption.
27,80,81,83
The temperature reduction goes along with a
slowdown of the global water cycle.
84,85
Global
precipitation is simulated to decrease by about
0.12 mm/day after the eruption. Again, the water cycle
response over land is stronger than over the ocean due
to the less strong ocean cooling. Model studies of
Tamboras climate effects suggest that the water cycle
response mainly affected the tropical rainforest and
ocean regions,
17
which is in line with model studies of
other large eruptions.
26,82,86
Tambora modeling stud-
ies further imply that the change in the land-sea ther-
mal contrast weakens the monsoonal circulations and
leads to drying in monsoon regions.
87
Volcanic erup-
tions may also change the temperature gradient
between the hemispheres. As a consequence, model
simulations indicate a southward movement of the
Intertropical Convergence Zone due to the increased
cooling of the Northern Hemisphere landmasses as
compared to the Southern Hemisphere oceans.
84,85
TABLE 1 |Overview of Tambora modelling studies indicating the forcings used and peak temperature changes over global land areas.
Estimates Indicated by Are Not Explicitly Given in the Cited Studies, But Have Been Calculated for This Publication
Study Aerosol/Forcing Model
Ensemble
Size Peak
D
T [K] Duration
Tambora-only sensitivity studies:
Stenchikov et al. (2009)
80
3×Pinatubo optical depth
(Stenchikov et al., 1998)
91
GFDL CM2.1 10 1.2 0.1 10 years
Zanchettin et al. (2013)
94
Crowley et al. (2008),
147
Crowley and Unterman (2013)
148
MPI-ESM 10 0.875 0.15 8 years
Kandlbauer et al. (2013)
83
Crowley et al. (2008)
147
HadGEM2-ES 5 1.0 0.1 10 years
Anet et al. (2014)
89
Arfeuille et al. (2014)
19
SOCOL-MPIOM 3 0.89 0.35
6 years
Muthers et al. (2014)
90
Arfeuille et al. (2014)
19
SOCOL-MPIOM 15 0.88 0.16/
0.80 0.26
67 years
Tambora in transient climate simulations driven only by volcanic forcing:
Otto-Bliesner et al. (2015)
149
Gao et al. (2008)
22
CESM-CAM5 5 0.95 0.12
6 years
Schurer et al. (2013)
150
Crowley and Unterman (2013)
148
HadCM3 3 1.30 0.05
7 years
Tambora in transient climate simulations with all major external forcings:
This study see Table 2 PMIP3/CMIP5
multimodel
mean (see
Table 2)
11 1.05 0.38 8 years
Tambora anomalies for all transient simulations were calculated relative to the less perturbed period of 17701799. The PMIP3/CMIP5 multimodel estimates
are based on a number of transient simulations for the last millennium (CCSM4 [1], GISS-E2-R [3], IPSL-CM5A-LR [1], MPI-ESM-P [1]) and an ensemble of
pre-CMIP3 simulations (COSMOS [5]). See Table 2 for the details.
TABLE 2 |Summary of the Past Millennium Simulations Used to Calculate the PMIP3/CMIP5 Multimodel Estimatefor Table 1
Model Runs Volcanic Forcing Reference
CCSM4 1 Gao et al. (2008)
22
Landrum et al. (2013)
151
GISS-E2-R 3 Gao et al. (2008),
22
Crowley and Unterman (2013)
148
Schmidt et al. (2014)
152
IPSL-CM5A-LR 1 Ammann et al. (2007)
153
Dufresne et al. (2013)
154
MPI-ESM-P 1 Crowley and Unterman (2013)
148
Jungclaus et al. (2014)
155
COSMOS 5 Crowley et al. (2008)
141
Jungclaus et al. (2010)
146
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Simulated regional scale temperature and precip-
itation responses to large tropical eruptions at
mid latitudes are heterogeneous. In summer, Western
and Central Europe become cool, but not Eastern
Europe.
82
Furthermore, an increase of summer precip-
itation is simulated over Southcentral Europe.
82,83,85
Both responses, which are also found in Tambora
simulations, are consistent with observations and
reconstructions.
88
The increase in precipitation
might be due to a weakening and expansion of the
Hadley Cell after the eruption.
82,89
Winter precipitation is reduced in Central and
Western Europe as well as over the US East Coast
and large parts of the Northern Pacic after large
eruptions, but increased over Northern Europe, con-
sistent with a positive NAO.
90
This is consistent with
observations.
The winter warming in Northeastern Europe
and positive NAO response following strong tropical
eruptions, which is well known from observations
and reconstructions,
88
is no longer well reproduced
by climate models.
9193
An overall reduction of win-
ter 500-hPa geopotential height is found in the
ensemble mean of simulations, but individual model
members are able to resemble the positive NAO
structure of the reconstructions with increased geo-
potential height over Southern Europe and strongly
negative anomalies over Iceland.
87,89,94
Additionally,
an intensication of the polar vortex after the Tam-
bora eruption is simulated,
90
which is hypothesized
as the underlying process of the positive NAO and
winter warming signal.
79,95,96
The starting point of this mechanism is the
stratosphere, where sulfate aerosols locally heat the
air by absorbing terrestrial infrared as well as solar
and terrestrial near-infrared radiation and reduce the
transfer of short-wave radiation into lower levels.
When the aerosols enter the stratosphere at tropical
latitudes as for Tambora they are lifted and globally
distributed by the BrewerDobson circulation. Ini-
tially most aerosols reside in the tropical stratosphere.
This unequal distribution of aerosols leads to unequal
distribution in absorbed radiation, which perturbs the
meridional and vertical temperature gradients in the
stratosphere. In winter, where the temperature distri-
bution has a strong inuence on the dynamics, the
polar vortex is strengthened and the vertical propaga-
tion of planetary waves is altered.
9599
The down-
ward propagation of these pronounced dynamical
changes is held responsible for the winter warming
signal over Northern to Central Europe.
89,90,9599
In comparison to the 2.5C warming observed
in the tropical stratosphere after Mount Pinatubo,
100
a stronger warming after Tambora is likely, although
the warming cannot be expected to scale linearly
with the aerosol mass, because the response also
depends on the microphysical properties of the aero-
sols.
101
Modeling studies suggest temperature
anomalies about two to four times that of
Pinatubo,
90,102104
but the response depends also on
the climate model and aerosol forcing applied. Simi-
larly, an intensication of the Northern Hemisphere
polar vortex can be expected
90,105
favoring positive
surface temperature anomalies in parts of the
NH SAT anomalies rel. to 1770–1799 [K]
–1
–2
1800 1810
Year AD
1820 1830
Otto–Bliesner et al. (2015)
Schurer et al. (2014)
This study
1840 1850
0
FIGURE 5 |Ensemble mean NH temperature anomalies in a number of transient simulations for the past millennium. See Table 1 for a
description of the models and volcanic forcing. Anomalies were calculated relative to the period 17701799.
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Northern Hemisphere higher latitudes in winter.
79
The strong forcing of the Tambora eruption is suf-
cient to induce wind anomalies that can alter the
propagation of planetary waves leading to a strength-
ening of the polar vortex.
104
Besides the dynamical perturbation in the strat-
osphere, the aerosols are also known to provide sur-
faces for a number of heterogeneous chemical
reactions that affect the chemical composition of the
stratosphere. After recent eruptions, pronounced
reductions of ozone were observed,
106
which are
suggested to amplify the dynamic response of the
stratosphere.
107,108
For Tambora, however, the
response of the ozone chemistry is assumed to be dif-
ferent. With low concentrations of ozone-depleting
substances a slight increase of ozone concentrations
is expected
109
(Figure 6) with no pronounced inu-
ences on stratospheric dynamics.
103,108
Nevertheless,
the choice of the ozone dataset in climate model
simulations has been shown to have substantial effect
on the dynamic response to the Tambora eruption.
90
Large volcanic eruptions like Tambora can
impact the ocean. Their signals in ocean heat content
may persist for decades, well beyond the lifetime of
stratospheric aerosols.
74,80,110
The Tambora eruption
arguably coincided with an El Niño event,
111
which
was also the case for the majority of other strong
tropical volcanic eruptions during the last 500 years.
This has raised the question of whether volcanic erup-
tions can excite El Niño events.
112114
Simulations
with a climate model of intermediate complexity show
that only volcanic eruptions larger than the Pinatubo
size can enhance the likelihood and amplitude of an El
Niño event.
73
McGregor and Timmermann
115
sug-
gested that while the dynamical thermostat mechanism
(i.e., the regulation of tropical Pacic sea surface tem-
peratures (SSTs) through a change in the zonal tem-
perature gradient and wind stress
116
) favors El Niño
events in simplied, spatially uniform set-ups, the
spatial gradients in mixed-layer depth, cloud albedo
and other variables modify the response and counter-
act the El Niño-like response. CMIP5 historical simu-
lations provide an opportunity to study this effect in a
multimodel ensemble. While Ding et al.
117
found only
a weak effect, Maher et al. found an El Niño response
in the year following volcanic eruptions, and then a
La Ninã 2 years later.
118
Stenchikov et al.
80
and Ottera et al.
119
showed
that major eruptions strengthen the Atlantic Meridio-
nal Overturning Circulation by a Sverdrup or more
on multidecadal timescales, and consequently
increase the northward heat transport. Possible
mechanisms for the increase include changes in
winter-time wind stress and density increases of polar
surface waters. However, the models vary greatly in
their simulated response.
113,120122
Furthermore,
cooling events, possibly also strong volcanic erup-
tions like Tambora, may trigger a coupled sea ice-
oceanatmosphere feedback in the North Atlantic
and the Nordic Seas.
123
The background state of the climate system
may play an important role in the post volcanic
response characteristics of the coupled sea ice-ocean
atmosphere. The decade 18101819 was unusually
cold in the Northern Hemisphere and the tropics due
to the combined effects of the unknown 1808/1809
(a)
–20 –10 –8 –4 –2 0
Column ozone anomalies [DU]
60°S
Januar y
May
September
Januar y
May
September
Januar y
May
September
Januar y
May
September
Januar y
May
September
Januar y
May
September
Januar y
May
September
Januar y
May
September
30°S
30°N
60°N
60°S
Present day Pre-industrial
30°S
30°N
60°N
248
10 20 30–30
(b)
FIGURE 6 |Zonal mean column ozone changes [DU] by heterogeneous chemical reactions in an ensemble of atmosphereocean-chemistry
climate simulations for a 4×Pinatubo eruption in a present day (left) and preindustrial (right) atmosphere (modied from Muthers et al.
103
).
Vertical dashed line indicates the beginning of the eruption. Signicant anomalies with respect to an ensemble of control simulations are shown
by stippling.
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and Tambora eruptions
124,125
and possibly decreased
solar activity. Zanchettin et al.
81
demonstrated for
the early 19th century that background conditions
have the potential to inuence the decadal climate
response to strong tropical volcanic eruptions. Near-
surface atmospheric and especially oceanic dynamics
in a set of MPI-ESM ensemble simulations evolve sig-
nicantly differently after the eruption under differ-
ent background conditions (Figure 7). In particular,
large interensemble member differences are found in
the post-Tambora decadal evolution of oceanic heat
transport and sea ice in the North Atlantic/Arctic
Ocean. They reveal the existence of multiple response
pathways after strong volcanic eruptions that depend
on background conditions prior to the eruptions.
Zanchettin et al.
126
showed that for very large
volcanic eruptions, contradictory to the Arctic, Ant-
arctic sea ice reacts mostly to dynamical atmospheric
Global surface net radiative flux anomaly Global near–surface air temperature anomaly
Ocean heat transport into Nordic Seas
Northern Hemisphere sea–ice cover
(c) (d)
(a) (b)
FIGURE 7 |Simulated global climate evolution of different variables in a 10 member ensemble of simulations including all natural and
anthropogenic forcing (black), a 10 member ensemble with only volcanic forcing including the Tambora and the preceding 1808/1809 eruption
(red), and a 10 member ensemble with only volcanic forcing without the 1808/1809 eruption (blue). The all forcing simulations are started in 1751
from initial conditions taken from the COSMOS-Mil experiments,
146
the volcanic forcing only from a control run for 800 AD conditions. Lines
indicate means. Shading indicates one standard error of the mean. Green dashed lines are the 5th95th percentile intervals for signal occurrence
in the control run (see second section). The inner dotted lines are the 10th90th percentile intervals. Magenta vertical lines indicate the occurrence
of the 1808/1809 and Tambora and Cosiguina eruptions. Bottom rectangles indicate periods when there is a signicant difference between an
ensemble (color same as for time series) and the other two. Positive surface net radiative ux anomalies correspond to increased downward ux.
The unit of the ocean heat transport is 1 TW = 10
12
W. (Reprinted with permission from Ref 81. Copyright 2013 John Wiley and Sons)
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changes initiated by the volcanically induced
strengthening of the Southern Hemispheres strato-
spheric polar vortex (positive SAM) and to local
feedback processes. After an initial post volcanic
short-lived expansion Antarctic sea ice undergoes a
prolonged contraction phase. Very large volcanic
forcing may therefore be a source of interhemispheric
interannual-to-decadal climate variability, although
the interhemispheric signature is weak in the case of
historical-size eruptions like Tambora.
Large volcanic eruptions, such as Tambora,
may also impact the carbon cycle.
96,127
The response
of the terrestrial biosphere and ocean biogeochemis-
try to volcanic eruptions sensitively depends on
changes in solar radiation (direct and diffuse), tem-
perature, precipitation, res, and atmospheric and
oceanic circulation. Although the exact mechanisms
causing a decrease in atmospheric CO
2
after volcanic
eruptions are poorly known, it is likely that the Tam-
bora eruption caused a decrease in atmospheric CO
2
concentration of a few ppm on decadal time-
scales.
83,110
It is also very likely that the volcanic
emissions of CO
2
during the Tambora eruption have
not signicantly impacted atmospheric CO
2.128
In modeling and atmospheric inversion studies,
focusing mainly on the Pinatubo eruption, the terres-
trial biosphere has been identied as the main driver
of atmospheric CO
2
changes, with minor temporary
contributions of the ocean.
83,110,129133
However, the
exact mechanisms (net primary production vs respi-
ration) by which the terrestrial biosphere drives a
decadal-scale decrease in atmospheric CO
2
as well as
the geographical distribution of changes are poorly
known (low latitudes vs high northern latitudes).
Modeling studies suggest that the sulfate aerosol-
induced cooling reduces heterotrophic respiration in
tropical and subtropical soils.
110,126,129131
This
increased soil carbon storage dominates over reduced
litter input due to precipitation and soil moisture
decrease and ultimately leads to increased terrestrial
carbon uptake and decreases in atmospheric CO
2
.
Other studies suggest more carbon uptake in north-
ern high latitudes,
133,134
or no change,
110
whereas
some studies predict a carbon source due to
decreased net primary production.
83,130,131
The ocean initially acts as a weak carbon sink
after a volcanic eruption, which is primarily due to
temperature-induced increase in CO
2
solubility in
low-latitude shallow waters. After the cooling signal
fades, the ocean is suggested to quickly transform
itself from a weak carbon sink to a weak carbon
source.
110,132
In addition to the suggested temperature and
precipitation driven changes on land, several studies
also suggest that an increase in diffuse radiation after
volcanic eruptions may enhance the terrestrial carbon
sink via enhanced net primary production.
135137
Others argue that this effect was probably only able
to compensate for the reduction in total radiation.
138
Recent laboratory experiments and direct evidence in
the North Pacic also indicate that the deposition of
volcanic ash on the oceanic surface may increase net
primary production in the ocean,
139141
but the
impact on atmospheric CO
2
remains unclear.
142
Most current coupled climate models do not include
these effects.
Although reconstructions from Antarctic ice
cores do not reveal signicant changes in CO
2
after
the Tambora eruption, which may be due to low
sampling resolution and diffusion within the archive,
modeling studies suggest that atmospheric CO
2
decreased by about 6 ppm after the Tambora erup-
tion.
83,110
The maximum decrease is delayed by a
couple of years compared to changes in sulfate aero-
sols and atmospheric temperature. The recovery of
the atmospheric CO
2
concentration takes longer than
for the bulk change in temperature as longer time-
scales are involved in the biogeochemical cycles than
in the physical processes of the atmosphere and the
surface ocean. Similarly to the ocean response
described above, Frölicher et al.
129
found that the
carbon cycle response to volcanic eruptions critically
depends on the initial conditions at the time of the
eruption, with a larger atmospheric CO
2
decrease
when volcanic eruptions occur during El Niño and in
winter than during La Niña conditions.
CONCLUSIONS
Since 1815 the world has not been faced with an
eruption of a similar strength as that of Tambora.
Still, the eruption has received great attention in the
sciences as it provides a rich testbed to deepen our
understanding of processes during enormous erup-
tions and related distant impacts. Certainly mankind
will be faced with such events in the future. The
bicentenary of the Tambora eruption provides a per-
fect opportunity to reconcile our current understand-
ing and to place the Tambora-specicndings in a
broader context of processes that are relevant during
and after volcanic eruptions.
During recent decades, processes during and
after Tambora have been intensively investigated,
narrowing down the potential volume to
~3050 km
3
.
1,17
The injection height might have
been up to 40 km, but the NBH (which is relevant
for the emissions) was more likely about 25 km. Still,
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the volume and particularly the interhemispheric dis-
tribution of the aerosols, as well as particles sizes, are
not well constrained and uncertainties about the
exact values remain.
Not only does the climate forcing of the Tam-
bora eruption have remaining uncertainties, but also
the details of the climate response. Instrumental data
give a detailed picture of weather and climate in spe-
cic regions following the eruption and allow addres-
sing, for example, increased synoptic activity over
Western Europe in the summer of 1816. However,
the instrumental data cover only Europe and parts of
North America. Nevertheless, advances in digitizing
early measurements from land and oceans and an
increasing network of highly resolved records from
different proxy archives have led to a better global
coverage of climate information in 1816 showing a
widespread reduction of surface air temperatures and
implications of the hydrological cycle in sensitive
areas like the monsoon regions. One key nding
from climate proxies is the absence of a strong Tam-
bora signal in the extratropical Southern Hemi-
sphere, while it is clearly expressed in the Northern
Hemisphere and Tropics. This is particularly intri-
guing as aerosol model studies suggest that transport
of aerosols was stronger toward the Southern Hemi-
sphere than the Northern Hemisphere and ice core
studies suggest equal partitioning or stronger trans-
port toward the Southern Hemisphere.
Modeling studies allow addressing possible,
physically consistent mechanisms, which may have
caused the observed signal. Simulations are able to
reproduce many aspects of post-Tambora climate as
found in observations and proxies. The mechanisms
are mostly the same as found for other strong tropi-
cal eruptions that are better constrained by observa-
tions (such as the Pinatubo eruption in 1991), but
the simulated signal is stronger. However, results are
sensitive to some of the uncertain parameters men-
tioned above. Hence, for future eruptions, one needs
to take these parameters into account to cover the
full uncertainty range. Moreover, climate model
simulations indicate that background conditions,
such as the preceding 1808/1809 eruption
(unknown) and possibly the Dalton Minimum of
solar activity were important for the climatic conse-
quences of the Tambora eruption, which also needs
to be taken into account when anticipating effects of
future eruptions.
The effect of volcanic eruptions on the biogeo-
chemical cycles has become an interesting research
topic. In particular, the simulated carbon cycle
response triggers a range of important new questions
for future research.
To advance our current understanding of the
dominant mechanisms behind simulated posteruption
climate evolution, but also more generally, of climate
dynamics and decadal variability, an international
model intercomparison project on the climatic
response to volcanic forcing (VolMIP)
143
has been
established for the 6th cycle of the Coupled Model
Intercomparison Project (CMIP6). In VolMIP, the
1815 Tambora eruption has been chosen as core
experiment, to address the long-term (up to the deca-
dal timescale) climate response to large volcanic
eruptions featuring a high signal-to-noise ratio in the
response of global-average surface temperature.
144
Although an improved knowledge about the climate
response after the Tambora eruption is expected
from the VOLMIP activity, it might still be a chal-
lenge to explain all observed regional climate
anomalies.
During the past decades, our scientic under-
standing of the Tambora eruption has grown tremen-
dously, and from studying the Tambora eruption,
science has gained insights into many complex
mechanisms operating in the climate system. Insights
have also been gained on sensitivity of the system to
boundary conditions, which is important for
enabling society to be prepared for future eruptions.
In this sense, science will undoubtedly keep learning
from Tambora.
ACKNOWLEDGMENTS
This paper is dedicated to the memory of Tom Crowley, who made substantial contributions to the under-
standing of the role of volcanic eruptions in the Earth system. We thank NCAR and the supercomputing
resources provided by NSF/CISL/Yellowstone for providing data from the CESM1 Last Millennium Ensemble
Community Project. S. Muthers was supported by the Swiss National Science Foundation Sinergia Project FUP-
SOL2 (CRSII2-147659). R. Auchmann was supported by the Swiss National Science Foundation Project
TWIST. C. Timmreck acknowledges funding from the BMBF project MIKLIP (FKZ:01LP1130A). R. Neukom
is funded by the SNSF (Ambizione grant PZ00P2_154802), T. L. Frölicher acknowledges nancial support
from the SNSF (Ambizione grant PZ00P2_142573). P. Brohan was supported by the Joint UK DECC/Defra
Met Ofce Hadley Centre Climate Programme (GA01101). A. Robock is supported by US National Science
Advanced Review wires.wiley.com/climatechange
© 2016 The Authors.
WIREs Climate Change
published by Wiley Periodicals, Inc.
Foundation grant AGS-1430051. A. Schurer and D. Zanchettin have provided model data. This paper was
partly the result of a conference supported by sponsored by the Oeschger Centre for Climate Change Research
of the University of Bern, the Swiss National Science Foundation, PAGES, SPARC, the Swiss Academy of
Sciences, and the Johanna Dürmüller-Bol Foundation. We thank Leonie Villiger for her help in the preparation
of the manuscript.
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WIREs Climate Change Tambora 1815 as a test case for high impact volcanic eruptions
© 2016 The Authors.
WIREs Climate Change
published by Wiley Periodicals, Inc.
... While the recent volcanic events (e.g., El Chichon and Pinatubo) have been well observed (and forcing effects are well replicated in models), the limited observational data for past volcanic eruptions lead to large uncertainties and biases in the aerosol particle size, hemispheric distributions, and radiative forcing estimates (Stenchikov et al. 2004;Santer et al. 2014;Toohey et al. 2011;Raible et al. 2016;Marshall et al. 2021Marshall et al. , 2022. The latest climate models with interactive volcanic aerosols have been shown to effectively simulate the aerosol loading, size distribution and associated climate response following the Pinatubo eruption (Mills et al. 2016(Mills et al. , 2017Niemeier et al. 2010). ...
... It is believed that the volcanic eruptions contribute greatly to climate variability, but quantifying these contributions is limited due to inconsistencies in the timing of volcanic aerosol loading and subsequent cooling signatures. Earlier studies have revealed that ENSO's response and sensitivity to eruptions over the past millennium appear to be significant, while important uncertainties remain (e.g., Raible et al. 2016;Dee et al. 2020;Hernández et al. 2020;Zhu et al. 2021Zhu et al. , 2022. Some studies suggest that a strong El Niño-like SST anomalous pattern occurs during eruption year that could persist for subsequent years, as shown in the observed 350 years (1649-2000) record (Adams et al. 2003). ...
... The intense radiative cooling caused by large tropical volcanic eruptions and allied changes in atmospheric circulation results in colder, saltier and therefore denser upper ocean conditions over convective regions, causing modifications to the oceanic thermohaline circulation (e.g., Otterå et al. 2010;Stenchikov et al. 2009;Raible et al. 2016;). This lets the cold signal to enter into the deep ocean and to substantially affect the global ocean temperature, sea level and heat content for several decades or even longer (Church et al. 2005;Delworth et al. 2005;Gleckler et al. 2006;Fasullo et al. 2016), thereby protracting the recovery of the climate system from volcanic perturbations. ...
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Understanding the influence of volcanism on ENSO and associated climatic impacts is of great scientific and social importance. Although many studies on the volcano–ENSO nexus are available, a thorough review of ENSO sensitivity to explosive eruptions is still missing. Therefore, this study aims to provide an in-depth assessment of the ENSO response to volcanism. Most past studies suggest an emerging consensus in models, with the vast majority showing an El Niño-like SST response during the eruption year and a La Niña-like response a few years later. RCP8.5-based climate model projections also suggest strong El Niño conditions and significant monsoonal rainfall reduction following strong tropical volcanism. However, some studies involving climate reconstructions and model simulations still raise concerns about the ENSO–volcano link and suggest a weak ENSO response to volcanism. This happens because ENSO response to volcanism seems very sensitive to reconstruction methods, ENSO preconditioning, eruption timing, position and amplitude. We noticed that some response mechanisms are still unclear, for instance, how the tropical volcanic forcing with nearly uniform radiative cooling projects onto ENSO when coincidental ENSO events are underway. Moreover, there are very less observational and proxy records for assessing the extratropical volcanism impact on ENSO. Nevertheless, model-based studies suggest that Northern (Southern) Hemispheric extratropical eruptions may lead to an El Niño (La Niña)-like response. We further noticed that the origin of post-eruption winter warming is still elusive; however, recent findings suggest that the large-scale circulation changes concurrently occurring during volcanism are the potential source of high-latitude winter warming. Existing uncertainties in the simulated ENSO response to volcanism could be reduced by considering a synchronized modeling approach with large ensembles.
... Those at low latitudes often produce global aerosol dispersion, whereas those in high-latitude areas, such as Iceland, typically disperse aerosols only in the hemisphere where they are located [3,4]. The global climatic impacts of some volcanic eruptions have left evident historical and environmental records, including the explosive eruptions of Tambora in 1815 CE [5] and Krakatau in 1883 CE [6] in Indonesia, as well as the longlasting fissure eruption of Laki in 1783/84 [7,8] in Iceland. These eruptions had effects on the global and regional temperatures, and they could also have effects on the hydrological cycle, changing the amounts of summer precipitation [9,10]. ...
... °C compared to the preceding 30 years. Large socioeconomic impacts following widespread crop failures and subsequent famines in 1816 have been partially associated with the Tambora eruption [5,54]. The 1257 eruption of the tropical Samalas volcano in Indonesia [55] was one of the largest eruptions of the Common Era [56]. ...
... This database seems to be well-suited for this study, since models project that the climate at the sampling sites (in the Alps between 45° and 47° northern latitude) is strongly influenced by both tropical and Icelandic eruptions, e.g., [3,74]. Moreover, observations, along with climate and glacier reconstructions, show a strong sensitivity of the alpine climate to volcanic forcing (e.g., [5,75,76]). We compared the isotopic values of tree-ring cellulose with proxies for the European climate and direct temperature measurements, as well as with the reconstructed temperatures based on the hydrogen isotope ratios of speleothem fluid inclusions from Milandre Cave in Switzerland [42], which provided information on the cold seasons not accessible from the tree-ring records. ...
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The importance of the stable isotopes in tree rings for the study of the climate variations caused by volcanic eruptions is still unclear. We studied δ18O, δD, δ13C stable isotopes of larch and cembran pine cellulose around four major eruptions with annual resolution, along with a superposed epoch analysis of 34 eruptions with 5-year resolution. Initial analysis of the tropical Tambora (1815 CE) and Samalas (1257 CE) eruptions showed a post-eruption decrease in δ18O values attributed to post-volcanic cooling and increased summer precipitation in Southern Europe, as documented by observations and climate simulations. The post-volcanic cooling was captured by the δD of speleothem fluid inclusion. The δ18O decrease was also observed in the analysis of 34 major tropical eruptions over the last 2000 years. In contrast, the eruptions of c. 750, 756, and 764 CE attributed to Icelandic volcanoes left no significant responses in the cellulose isotopes. Further analysis of all major Icelandic eruptions in the last 2000 years showed no consistent isotopic fingerprints, with the exception of lower post-volcanic δ13C values in larch. In summary, the δ18O values of cellulose can provide relevant information on climatic and hydroclimatic variations following major tropical volcanic eruptions, even when using the 5-year resolution wood samples of the Alpine Tree-Ring Isotope Record database.
... Robock, 2000;von Savigny et al., 2020). Prominent examples of volcanic eruptions with significant climatic effects are the 1815 eruption of Tambora, which led to the year without summer in 1816 (Raible et al., 2016), and the 1991 eruption of Mt. Pinatubo. ...
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The idea of estimating stratospheric aerosol optical thickness from the twilight colours in historic paintings – particularly under conditions of volcanically enhanced stratospheric aerosol loading – is very tantalizing because it would provide information on the stratospheric aerosol loading over a period of several centuries. This idea has in fact been applied in a few studies in order to provide quantitative estimates of the aerosol optical depth after some of the major volcanic eruptions that occurred during the past 500 years. In this study we critically review this approach and come to the conclusion that the uncertainties in the estimated aerosol optical depths are so large that the values have to be considered questionable. We show that several auxiliary parameters – which are typically poorly known for historic eruptions – can have a similar effect on the red–green colour ratio as a change in optical depth typically associated with eruptions such as, for example, Tambora in 1815 or Krakatoa in 1883. Among the effects considered here, uncertainties in the aerosol particle size distribution have the largest impact on the colour ratios and hence the aerosol optical depth estimate. For solar zenith angles exceeding 80∘, uncertainties in the stratospheric ozone amount can also have a significant impact on the colour ratios. In addition, for solar zenith angles exceeding 90∘ the colour ratios exhibit a dramatic dependence on solar zenith angle, rendering the estimation of aerosol optical depth highly challenging. A quantitative determination of the aerosol optical depth may be possible for individual paintings for which all relevant parameters are sufficiently well constrained in order to reduce the related errors.
... We choose a length N = 20 205 years to analyse the temperature response to volcanic forcing, and a length N = 200 years to analyse the response to solar forcing. The former encompasses the recovery time even after a large volcanic eruption such as Tambora generously (Schurer et al., 2013;Otto-Bliesner et al., 2016;Raible et al., 2016). The latter encompasses a full solar cycle, which has an amplitude of around 200 years ( Fig. 1 (b)). ...
Preprint
Full-text available
Here we investigate how uncertainties in the solar and volcanic forcing records of the past millennium affect the large-scale temperature response of a 2-box impulse response model. We use different published solar forcing records and present a new volcanic forcing ensemble which accounts for random uncertainties in eruption dating and sulfur injection amount. The simulations are compared to proxy reconstructions from PAGES 2k and Northern hemispheric tree-ring data. We find that low solar forcing is most consistent with all the proxy reconstructions, even when accounting for volcanic uncertainty and that the residuals are well in line with CMIP6 control variability at centennial timescales. Volcanic forcing uncertainty induces a significant spread in the temperature response, especially at periods of peak forcing. For individual eruptions and superposed epoch analyses volcanic uncertainty can strongly affect the agreement with proxy reconstructions, and may explain previous proxy-model discrepancies.
... The overall top-of-the-atmosphere (TOA) effect is an increase in the amount of radiation reflected back to space, leading to net negative radiative forcing [2]. The imbalance in the Earth's radiation budget induced by the influence of energetic volcanic eruptions injecting aerosols to the stratosphere, such as the Tambora (1815) [3], El Chichón (1982) [4] and Pinatubo (1991) eruptions [5], is fed back to the troposphere, leading to changes in temperature, precipitation and atmospheric circulation on timescales of months to years (e.g., [6][7][8]). ...
Article
The Hunga Tonga-Hunga Ha’apai eruption on January 15, 2022 was one of the most explosive volcanic eruptions of the 21st century and has attracted global attention. Here we show that large amounts of the volcanic aerosols from the eruption broke through the tropopause into the lower stratosphere, forming an ash plume with an overshooting top at 25–30 km altitude. In the four days following the eruption, the ash plume moved rapidly westward for nearly 10,000 km under stable stratospheric conditions characterized by strong tropical easterlies, weak meridional winds and weak vertical motion. The intrusion of the ash plume into the stratosphere resulted in a marked increase in atmospheric aerosol loading across northern Australia, with the aerosol optical depth (AOD) observed by satellites and sun-photometers peaking at 1.5 off the coast of northeastern Australia; these effects lasted for nearly three days. The ash plume was characterized by fine-mode particles clustered at a radius of about 0.26 µm, with an observed peak volume of 0.25 µm⁻³ µm⁻². The impact of the ash plume associated with the Hunga Tonga eruption on the stratospheric AOD and radiative balance in the tropical southern hemisphere is remarkable, with an observed volcanic-induced perturbation of the regional stratospheric AOD of up to 0.6. This perturbation largely explains an instantaneous bottom (top) of the atmosphere radiative forcing of −105.0 (−65.0) W m⁻² on a regional scale.
... Tambora's devastating eruption in 1815 resulted in >90,000 casualties from volcanic impacts including pyroclastic deposits, tsunamis and drought (e.g., Self et al., 1984;Zaennudin, 2010). Injection of ash and sulfur gases into the atmosphere from the explosive eruption impacted the global climate (e.g., Raible et al., 2016;Stothers and Rampino, 1983). The 1815 eruption has been relatively well studied through geological and petrological surveys of the deposits (e.g., Foden, 1986;Self et al., 1984;Sutawidjaja et al., 2006). ...
Article
Routine analysis and detection of volcanic thermal features (VTFs) are available globally for low spatial resolution (>1 km/pixel) thermal infrared (TIR) sensors. However, medium resolution (90 m/pixel) ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) TIR data, which is sensitive to smaller and cooler VTFs, have yet to be systematically examined at all active Indonesian volcanoes. We manually examined cloud-free nighttime images at 136 potentially active volcanoes from 2000 to 2020 CE and found at least 71 volcanoes with VTFs, despite the low proportion (26.5%) of cloud-free images. Of these, 34 volcanoes have VTF detections from space published for the first time (to our knowledge) and at least 44 volcanoes have non-eruptive VTFs (fumaroles, heated volcanic lakes and open vent systems). The inclusion of hotspots detected by ASTER in this study increases the percentage of Indonesian volcanoes with recorded satellite-detectable thermal features from 27% to 52%, larger than in Latin America (27%) and the US (33%) which were surveyed in the same way and is possibly due to a higher frequency of eruptions in Indonesia. The distribution of VTFs across sub-regions in Indonesia is not uniform but may be correlated with the number of volcanoes with eruptions. This multi-decadal country-wide survey highlights the potential of TIR monitoring and detection of low-temperature volcanic features that may be eruption precursors, but also the limits of the available datasets since many volcanoes only have a few cloud-free nighttime images per year.
... By injecting large amounts of sulfur into the atmosphere and thereby reducing the insolation reaching the Earth's surface (Robock, 2000), volcanic eruptions have been identified as the main drivers of natural climate variability on interannual to decadal timescales. They have been responsible for numerous cooling extremes in the past 2500 years (Anchukaitis et al., 2012;Guillet et al., 2017;McConnell et al., 2020a;Stoffel et al., 2015;Tejedor et al., 2021;Toohey et al., , 2016a, often promoting crop failures and famines (Büntgen et al., , 2016Helama et al., 2018;Huhtamaa and Helama, 2017;Gao et al., 2021;Luterbacher and Pfister, 2015;McConnell et al., 2020b;Raible et al., 2016). Earth's largest volcanic eruptions (Crosweller et al., 2012;Mason et al., 2004) since the emergence of human civilization were more than an order of magnitude larger than the largest eruptions (e.g., Pinatubo 1991) for which we have direct observational evidence of the resulting atmospheric radiative perturbations and associated climatic effects (Douglass and Knox, 2005;Graf et al., 1993;Kremser et al., 2016). ...
Article
The injection of sulfur into the stratosphere by volcanic eruptions is the dominant driver of natural climate variability on interannual to multidecadal timescales. Based on a set of continuous sulfate and sulfur records from a suite of ice cores from Greenland and Antarctica, the HolVol v.1.0 database includes estimates of the magnitudes and approximate source latitudes of major volcanic stratospheric sulfur injection (VSSI) events for the Holocene (from 9500 BCE or 11 500 years BP to 1900 CE), constituting an extension of the previous record by 7000 years. The database incorporates new-generation ice-core aerosol records with a sub-annual temporal resolution and a demonstrated sub-decadal dating accuracy and precision. By tightly aligning and stacking the ice-core records on the WD2014 chronology from Antarctica, we resolve long-standing inconsistencies in the dating of ancient volcanic eruptions that arise from biased (i.e., dated too old) ice-core chronologies over the Holocene for Greenland. We reconstruct a total of 850 volcanic eruptions with injections in excess of 1 teragram of sulfur (Tg S); of these eruptions, 329 (39 %) are located in the low latitudes with bipolar sulfate deposition, 426 (50 %) are located in the Northern Hemisphere extratropics (NHET) and 88 (10 %) are located in the Southern Hemisphere extratropics (SHET). The spatial distribution of the reconstructed eruption locations is in agreement with prior reconstructions for the past 2500 years. In total, these eruptions injected 7410 Tg S into the stratosphere: 70 % from tropical eruptions and 25 % from NH extratropical eruptions. A long-term latitudinally and monthly resolved stratospheric aerosol optical depth (SAOD) time series is reconstructed from the HolVol VSSI estimates, representing the first Holocene-scale reconstruction constrained by Greenland and Antarctica ice cores. These new long-term reconstructions of past VSSI and SAOD variability confirm evidence from regional volcanic eruption chronologies (e.g., from Iceland) in showing that the Early Holocene (9500–7000 BCE) experienced a higher number of volcanic eruptions (+16 %) and cumulative VSSI (+86 %) compared with the past 2500 years. This increase coincides with the rapid retreat of ice sheets during deglaciation, providing context for potential future increases in volcanic activity in regions under projected glacier melting in the 21st century. The reconstructed VSSI and SAOD data are available at https://doi.org/10.1594/PANGAEA.928646 (Sigl et al., 2021).
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Although collaborative efforts have been made to retrieve climate data from instrumental observations and paleoclimate records, there is still a large amount of valuable information in historical archives that has not been utilized for climate reconstruction. Due to the qualitative nature of these datasets, historical texts have been compiled and studied by historians aiming to describe the climate impact in socioeconomic aspects of human societies, but the inclusion of this information in past climate reconstructions remains fairly unexplored. Within this context, we present a novel approach to assimilate climate information contained in chronicles and annals from the 15th century to generate robust temperature and precipitation reconstructions of the Burgundian Low Countries, taking into account uncertainties associated with the descriptions of narrative sources. After data assimilation, our reconstructions present a high seasonal temperature correlation of ∼0.8 independently of the climate model employed to estimate the background state of the atmosphere. Our study aims to be a first step towards a more quantitative use of available information contained in historical texts, showing how Bayesian inference can help the climate community with this endeavor.
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This chapter describes how volcanic emissions into the troposphere and stratosphere affect aerosol properties, radiation, and climate. It begins by describing aerosol and precursor gas emissions from passive degassing and volcanic eruptions, including a time history of emissions over the satellite era since 1978. It describes how records of volcanism and volcanic effects on climate can be reconstructed from ice cores, tree rings, and written historical records. It then describes how volcanic emissions affect aerosol physical and optical properties and how these alter atmospheric radiation and global temperature. The chapter concludes by outlining the status of models and the challenges in using them to quantitatively link volcanic sulfate deposition records in ice cores to their climatic effects.
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Alexander von Humboldt is often depicted as a pioneer of “Earth System Science”. He seems to have anticipated many of the current concepts of Earth System Science and described them in an accurate language. These concepts include the interconnectedness of the system, the human influence on it as well as consequent repercussions for humans. Alexander von Humboldt’s “Earth System thinking” also expressed itself in the methodologies used and is an important basis of Humboldt’s empiricism. Only an accurate notion of the Earth System allows to make optimal use of the myriads of individual observations collected by Humboldt. Moreover, his graphical depictions of the Earth System allowed him “drawing” conclusions. However, claiming Humboldt to be the first Earth System scientists is also a projection of our current view back onto Humboldt, all the more as there has been no continuity. Current Earth System Science developed independently, from different precedents and in a different scientific context. It has important roots in the 1950s, perhaps with Vernadsky as an even earlier forerunner, but developed mainly in the 1980s, without reference to Humboldt. Conversely, Humboldt’s notion was broader than current Earth System Science in that it included sensual and aesthetical aspects and linked science to the human experience.KeywordsClimatologyEarth system sciencesAnthropogenic influence
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This report describes details of developing a volcano forcing reconstruction (Crowley et al., 2008) for climate models that is based primarily on sulphate records in Antarctic and Greenland ice cores. The chronology of eruptions is considered accurate to within 1 yr for the interval AD 1104–2000 and about 2 yr for AD 800–1103. The reconstruction involves (1) calibration against satellite aerosol optical depth (AOD) estimates of the 1991 Pinatubo/Hudson eruptions; (2) partial validation against independent lunar estimates of AOD and global sulphate emissions; (3) partial assessment of uncertainties in AOD estimates; (4) assessment of possible tropical "false positives" in ice core reconstructions due to simultaneous occurrence of mid/high-latitude eruptions in each hemisphere; (5) identification of a new category of eruptions, termed "unipolar" tropical eruptions, in which the eruption plume penetrates mainly to polar regions in only the hemisphere of its eruption; (6) use of different growth curves for high- and low-latitude eruptions; (7) specification of 2/3 power shortwave scaling for eruptions larger than the 1991 Pinatubo eruption; (8) introduction of an estimate of effective particle size that affects lifetime and scattering properties of stratospheric aerosols; and (9) utilization of bimonthly-resolution electrical conductivity measurements to estimate the eruption date of the 1258/1259 eruption as 1257.7±0.2. The data, and a high-temporal resolution reconstruction for climate models, are available at: http://hurricane.ncdc.noaa.gov/pls/paleox/f?p=519:1:::::P1_STUDY_ID:14168.
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The response of atmospheric chemistry and dynamics to volcanic eruptions and to a decrease in solar activity during the Dalton Minimum is investigated with the fully coupled atmosphere–ocean chemistry general circulation model SOCOL-MPIOM (modeling tools for studies of SOlar Climate Ozone Links-Max Planck Institute Ocean Model) covering the time period 1780 to 1840 AD. We carried out several sensitivity ensemble experiments to separate the effects of (i) reduced solar ultra-violet (UV) irradiance, (ii) reduced solar visible and near infrared irradiance, (iii) enhanced galactic cosmic ray intensity as well as less intensive solar energetic proton events and auroral electron precipitation, and (iv) volcanic aerosols. The introduced changes of UV irradiance and volcanic aerosols significantly influence stratospheric dynamics in the early 19th century, whereas changes in the visible part of the spectrum and energetic particles have smaller effects. A reduction of UV irradiance by 15%, which represents the presently discussed highest estimate of UV irradiance change caused by solar activity changes, causes global ozone decrease below the stratopause reaching as much as 8% in the midlatitudes at 5 hPa and a significant stratospheric cooling of up to 2 °C in the mid-stratosphere and to 6 °C in the lower mesosphere. Changes in energetic particle precipitation lead only to minor changes in the yearly averaged temperature fields in the stratosphere. Volcanic aerosols heat the tropical lower stratosphere, allowing more water vapour to enter the tropical stratosphere, which, via HOx reactions, decreases upper stratospheric and mesospheric ozone by roughly 4%. Conversely, heterogeneous chemistry on aerosols reduces stratospheric NOx, leading to a 12% ozone increase in the tropics, whereas a decrease in ozone of up to 5% is found over Antarctica in boreal winter. The linear superposition of the different contributions is not equivalent to the response obtained in a simulation when all forcing factors are applied during the Dalton Minimum (DM) – this effect is especially well visible for NOx/NOy. Thus, this study also shows the non-linear behaviour of the coupled chemistry-climate system. Finally, we conclude that especially UV and volcanic eruptions dominate the changes in the ozone, temperature and dynamics while the NOx field is dominated by the energetic particle precipitation. Visible radiation changes have only very minor effects on both stratospheric dynamics and chemistry.
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The decadal evolution of Arctic and Antarctic sea ice following strong volcanic eruptions is investigated in four climate simulation ensembles performed with the COSMOS-Mill version of the Max Planck Institute Earth System Model. The ensembles differ in the magnitude of the imposed volcanic perturbations, with sizes representative of historical tropical eruptions (1991 Pinatubo and 1815 Tambora) and of tropical and extra-tropical "supervolcano" eruptions. A post-eruption Arctic sea-ice expansion is robustly detected in all ensembles, while Antarctic sea ice responds only to supervolcano eruptions, undergoing an initial short-lived expansion and a subsequent prolonged contraction phase. Strong volcanic forcing therefore emerges as a potential source of inter-hemispheric interannual-to-decadal climate variability, although the inter-hemispheric signature is weak in the case of eruptions comparable to historical eruptions. The post-eruption inter-hemispheric decadal asymmetry in sea ice is interpreted as a consequence mainly of the different exposure of Arctic and Antarctic regional climates to induced meridional heat transport changes and of dominating local feedbacks that set in within the Antarctic region. Supervolcano experiments help to clarify differences in simulated hemispheric internal dynamics related to imposed negative net radiative imbalances, including the relative importance of the thermal and dynamical components of the sea-ice response. Supervolcano experiments could therefore serve the assessment of climate models' behavior under strong external forcing conditions and, consequently, favor advancements in our understanding of simulated sea-ice dynamics.
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The oceanic response to volcanic eruptions over the last 1000 years is investigated with a focus on the North Atlantic Ocean, using a fully coupled AOGCM forced by a realistic time series of volcanic eruptions, total solar irradiance (TSI) and atmospheric greenhouse gases concentration. The model simulates little response to TSI variations but a strong and long-lasting thermal and dynamical oceanic adjustment to volcanic forcing, which is shown to be a function of the time period of the volcanic eruptions. The thermal response consists of a fast tropical cooling due to the radiative forcing by the volcanic eruptions, followed by a penetration of this cooling in the subtropical ocean interior one to five years after the eruption, and propagation of the anomalies toward the high latitudes. The oceanic circulation first adjusts rapidly to low latitude anomalous wind stress induced by the strong cooling. The Atlantic Meridional Overturning Circulation (AMOC) shows a significant intensification 5 to 10 years after the eruptions of the period post-1400 A.D., in response to anomalous atmospheric momentum forcing, and a slight weakening in the following decade. In response to the stronger eruptions occurring between 1100 and 1300, the AMOC shows no intensification and a stronger reduction after 10 years. This study thus stresses the diversity of AMOC response to volcanic eruptions in climate models and discusses possible explanations.
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John Kington's book, the first of its kind, gives a definitive account of the weather in the 1780s over Europe based on historical weather maps. These charts are unique in forming the earliest series of daily synoptic weather maps constructed with quantitative instrumental data, and as such represent an important contribution to the history of climate.
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Earth’s climate is undergoing profound changes. Understanding and assessing these changes requires insight from the past. The period since 1700 is of particular relevance because Earth’s climate underwent a transition from the Little Ice Age climate to the era of anthropogenic global warming. Moreover, pronounced climatic excursions occurred on interannual and decadal time scales, and atmospheric composition changed. Recent developments in the fields of paleoclimatology and historical climatology – high-resolution climate proxies, climate model simulations, and numerical techniques such as data assimilation – allow a much more detailed analysis of climatic changes of the past centuries than possible only a decade ago. “Climatic Changes since 1700” – the title honours the 1890 book by the same title of geographer Eduard Brückner – covers data and methods used to study climate of the past centuries, summarises the mechanisms behind interannual to multidecadal climate variability and provides an overview of global climate history since 1700 based on new data sets and model simulations.