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Global Warming Baselines Conversion Factors
Joseph Nowarski, M.Sc., ME – Energy Conservation Expert
Version 1.1.1, 21 March 2022
DOI:10.5281/zenodo.6373058
Abstract
This publication includes a conversion table between various baselines of global
surface temperature changes.
The conversion factor from 1951-1980 to 1850-1900 baseline is +0.31°C for
land+ocean, +0.49°C for land only, and +0.29°C for ocean only.
Glossary
Ave average
BL baseline
CF conversion factor between baselines or reference periods
DB dataset, database
LBL Berkeley Earth (Lawrence Berkeley Laboratory)
Units
The temperature change unit in this work is °C.
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Global Temperature Databases
There are few databases of annual averages of global surface temperature
changes.
Each database applies its own baseline.
This work includes the following databases:
NASA [1] [2]
NOAA [3]
Berkeley Earth (LBL) [4] [5] [6]
Air Temperature and Surface Temperature
The difference between the air temperature and surface temperature is explained
in [9].
Air temperature is measured at a standard height of 1.2 m above the ground
surface. Air temperature can be quite different from surface temperature. In
general, air temperatures above a surface reflect the same trends as ground
surface temperatures, but ground temperatures are likely to be more extreme [9].
Global Warming Baselines
The EU aims to be climate-neutral by 2050 – an economy with net-zero greenhouse
gas emissions [7].
The EU policy is "in line with the Paris Agreement to keep the global temperature
increase to well below 2°C and pursue efforts to keep it to 1.5°C" [7].
The EU determines the “global temperature increase” according to the IPCC
baseline 1850-1900 [8].
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IPCC Report 2011 [8] page 5 note 9: “The period 1850–1900 represents the earliest
period of sufficiently globally complete observations to estimate global surface
temperature and, consistent with AR5 and SR1.5, is used as an approximation for
pre-industrial conditions”.
However, all main databases apply other baselines than IPCC and EU. NASA [1] [2]
and Berkeley Earth [4] [5] [6] apply the 1951-1980 baseline, and NOAA[3] applies
the 20th century baseline, 1901-2000.
The NASA and NOA databases are from 1880 and not 1850.
It takes a lot of effort to find conversion factors between the IPCC 1850-1900
baseline and the main exiting databases, which have different baselines. The
example of such efforts may be a long blog on site Climate Lab Book - Defining
‘pre-industrial’ [10], concluded with the following statement of Mark Bassham:
“IPCC AR5 (WG1 report), Figure 12.40 (page 1100) indicates a difference between
‘pre-industrial’ temperatures and the 1980-1999 Reference Period (non-standard,
only 20 years long instead of the usual 30) of EXACTLY 0.5°C. Note that ‘pre-
industrial’ means different things to different IPCC Chapter Lead Authors”.
Conversion Factors for Land+Ocean
Table 1 - Global surface temperature change databases for land+ocean
NASA NOAA LBL
Reference [1] [2] [3] [4] [5]
Units °C °C °C
from 1880 1880 1850
to 2021 2020 2021
Years 142 141 172
Baseline (BL) 1951-1980 1901-2000 1951-1980
BL years 30 100 30
Decimal places 2 2 3
Ave in BL +0.0003 +0.0004 +0.0171
Publication [10] includes the following conversion factor: “IPCC AR5 (WG1 report),
Figure 12.40 (page 1100) indicates a difference between ‘pre-industrial’
temperatures and the 1980-1999 Reference Period … of EXACTLY 0.5°C”.
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The publication of the European Commission’s Competence Center on Composite
Indicators and Scoreboards [11] includes the following conversion factor to the
1850-1900 baseline: "Global temperature change (1850-2012): IPCC AR5: change
from 1850-1900 baseline to 1986-2005 is 0.61 ± 0.10°C".
IPCC 2021 Report [8] p5 item A.1.2 indicates the following relations between the
1850-1900 baseline and other periods: “Global surface temperature in the first two
decades of the 21st century (2001–2020) was 0.99 [0.84 to 1.10] °C higher than
1850–1900. Global surface temperature was 1.09 [0.95 to 1.20] °C higher in 2011–
2020 than 1850–1900”.
The above publications require determination of averages in additional reference
periods:
1980-1999 [10]
1986-2005 [11]
2001-2020 [8]
2011-2020 [8]
Table 2 - Baselines and reference periods
BL NASA NOAA LBL IPCC IPCC
Reference [1] [2] [3] [4.1] [5.1] [10] [11] [8.1] [8.2]
DB BL 1951-1980 1901-2000 1951-1980
1850-1900 -0.30 +0.00 +0.00 +0.00 +0.00
1901-2000 -0.03 +0.00 -0.02
1951-1980 +0.00 +0.04 +0.02
1980-1999 +0.32 +0.34 +0.36 +0.50
1986-2005 +0.42 +0.45 +0.47 +0.61
2001–2020 +0.73 +0.72 +0.77 +0.99
2011-2020 +0.84 +0.82 +0.88 +1.09
DB BL Baseline of the database
The green background highlights the baseline period of the data.
The values in the above table for NASA, NOAA and LBL were calculated as
averages in other reference periods.
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Table 3 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to reference [10] and NASA database [°C]
Ref from to °C
[10] 1850-1900 1980-1999 +0.50
NASA 1951-1980 1980-1999 +0.32
Δ 1850-1900 1951-1980 +0.18
CF 1951-1980 1850-1900 +0.18
CF estimated conversion factor [°C]
Table 4 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to reference [11] and NASA database [°C]
Ref from to °C
[11] 1850-1900 1986-2005
+0.61
NASA 1951-1980 1986-2005
+0.42
Δ 1850-1900 1951-1980 +0.19
CF 1951-1980 1850-1900 +0.19
Table 5 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to reference [8.1] and NASA database [°C]
Ref from to °C
[8.1] 1850-1900 2001–2020
+0.99
NASA 1951-1980 2001–2020
+0.73
Δ 1850-1900 1951-1980 +0.26
CF 1951-1980 1850-1900 +0.26
Table 6 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to reference [8.2] and NASA database [°C]
Ref from to °C
[8.2] 1850-1900 2011-2020 +1.09
NASA 1951-1980 2011-2020 +0.84
Δ 1850-1900 1951-1980 +0.26
CF 1951-1980 1850-1900 +0.26
Berkeley Earth (LBL) Database [4.1] [5.1] includes records from 1850, allowing
calculation of averages in 1951-1980 and 1850-1900 periods for land+ocean. The
difference between the averages in both periods is an estimation of the
conversion factor from 1951-1980 to 1850-1900 baselines.
Table 7 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to LBL [4.1] [5.1] database [°C]
Ref from to °C
[4.1] [5.1] 1951-1980 1850-1900 -0.30
CF 1951-1980 1850-1900 +0.30
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Berkeley Earth (LBL) [4.2] [5.2] clearly indicates the conversion factor between
1951-1980 and 1850-1900 baselines: "The global mean temperature in 2021 is
estimated to have been 1.21 °C above the average temperature from 1850-1900,
a period often used as a pre-industrial baseline for global temperature targets. This
temperature in 2021 is equivalent to 0.90 °C above the 1951-1980 average which is
often used as a reference period for comparing global climate analyses".
Table 8 - LBL [4.2] [5.2] conversion factor from 1951-1980 to 1850-1900 baseline
[°C]
Ref from to °C
[4.2] [5.2] 1850-1900 2021 +1.21
[4.2] [5.2] 1951-1980 2021 +0.90
Δ 1850-1900 1951-1980 +0.31
CF 1951-1980 1850-1900 +0.31
Table 9 - All estimations of the conversion factor from 1951-1980 to 1850-1900
baseline for land+ocean [°C]
Ref [10] [11] [8.1] [8.2] [4.1] [5.1] [4.2] [5.2] *
°C °C °C °C °C °C
CF +0.18 +0.19 +0.26 +0.26 +0.30 +0.31
* selected conversion factor
Among all above options, the only case of direct conversion between 1951-1980
and 1850-1900 baseline is Berkeley Earth [4.2] [5.2]: "The global mean temperature
in 2021 is estimated to have been 1.21 °C above the average temperature from
1850-1900, a period often used as a pre-industrial baseline for global temperature
targets. This temperature in 2021 is equivalent to 0.90 °C above the 1951-1980
average which is often used as a reference period for comparing global climate
analyses".
The conversion factor from 1951-1980 to 1850-1900 baseline for land+ocean
selected for further analysis and conversion of the databases in this work is +0.31°C.
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Table 10 - Databases and baselines for estimations of conversion factor from
1901-2000 to 1850-1900 baseline
BL NASA NOAA LBL
Reference [1] [2] [3] [4.1] [5.1]
DB BL 1951-1980 1901-2000 1951-1980
1850-1900 -0.30
1901-2000 -0.03 +0.00 -0.02
1951-1980 +0.00 +0.04 +0.02
Table 11 - Estimation of conversion factor from 1901-2000 to 1850-1900 baseline
according to LBL [4.1] [5.1] database [°C]
Ref from to °C
LBL 1951-1980 1850-1900 -0.30
LBL 1951-1980 1901-2000 -0.02
Δ 1850-1900 1951-1980 -0.28
CF 1901-2000 1850-1900 +0.28
Table 12 - Estimation of conversion factor from 1901-2000 to 1850-1900 baseline
according to conversion factor from 1951-1980 to 1850-1900 and NASA
database [°C]
Ref from to °C
CF 1951-1980 1850-1900 +0.31
NASA 1951-1980 1901-2000 -0.03
CF 1901-2000 1850-1900 +0.28
Table 13 - Estimation of conversion factor from 1901-2000 to 1850-1900 baseline
according to conversion factor from 1951-1980 to 1850-1900 and NOAA
database [°C]
Ref from to °C
CF 1951-1980 1850-1900 +0.31
NOAA 1951-1980 1901-2000 -0.04
CF 1901-2000 1850-1900 +0.27
Table 14 - All estimations of the conversion factor from 1901-2000 to 1850-1900
baseline for land+ocean [°C]
Ref LBL NASA NOAA Ave *
°C °C °C °C
CF +0.28 +0.28 +0.27 +0.28
* selected conversion factor
As there is no example of direct conversion from 1901-2000 to 1850-1900 baseline,
the average of all estimations +0.28°C will be applied for further analysis and
conversion of the databases in this work.
Global Warming Baselines Conversion Factors - Joseph Nowarski
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Table 15 - Conversion factors to 1850-1900 baseline for land+ocean [°C]
from BL: Land+Ocean
1850-1900 +0.00
1901-2000 +0.28
1951-1980 +0.31
Conversion Factors for Land Only
IPCC 2021 Report [8] p5 item A.1.2 indicates the following relations between the
1850-1900 baseline and other periods: “Global surface temperature was 1.09 [0.95
to 1.20] °C higher in 2011–2020 than 1850–1900, with larger increases over land
(1.59 [1.34 to 1.83] °C) than over the ocean (0.88 [0.68 to 1.01] °C)”.
According to the NASA database, the average temperature change for land only
in the 2011–2020 period was 1.24°C above the 1951-1980 baseline.
According to Berkeley Earth (LBL) [4] [5] "in 2021, the land average temperature
was 1.70 ± 0.04 °C above the average temperature from 1850 to 1900".
According to the NASA database, the temperature change for land only in
2021was 1.32°C above the 1951-1980 baseline.
Table 16 - Databases for land only
NASA LBL
Reference [1] [2] [6]
Units °C °C
Records annual monthly
from 1880 1750
to 2021 2021
years 142 272
Baseline (BL) 1951-1980 1951-1980
BL years 30 30
Decimal places 2 3
Ave in BL +0.0010 +0.0010
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Table 17 - Baselines and reference periods
IPCC LBL NASA LBL
Reference [8] [4] [5] [1] [2] [6]
1850-1900 +0.00 +0.00 -0.49
1901-2000 +0.00
1951-1980 +0.00 +0.00
2011-2020 +1.59 +1.24 +1.17
2021 +1.70 +1.32 +1.24
Table 18 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to reference [8] and NASA database [°C]
Ref from to °C
[8] 1850-1900 2011-2020 +1.59
NASA 1951-1980 2011-2020 +1.24
Δ 1850-1900 1951-1980 +0.35
CF 1951-1980 1850-1900 +0.35
Table 19 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to reference [4] [5] and NASA database [°C]
Ref from to °C
[4] [5] 1850-1900 2021 +1.70
NASA 1951-1980 2021 +1.32
Δ 1850-1900 1951-1980 +0.38
CF 1951-1980 1850-1900 +0.38
Berkeley Earth (LBL) database [6] is from 1750, which allows calculations of
averages in any reference period. In the current work, annual averages were
calculated based on the LBL [6] monthly data from January to December for each
year of the database. The annual results of these calculations are publicly
available in publication [12].
Table 20 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to Berkeley Earth (LBL) [6] [°C]
Ref from to °C
LBL [6] 1951-1980 1850-1900 -0.49
CF 1951-1980 1850-1900 +0.49
Table 21 - All estimations of the conversion factor from 1951-1980 to 1850-1900
baseline for land only [°C]
Ref [8] [4] [5] LBL [6] *
°C °C °C
CF +0.35 +0.38 +0.49
* selected conversion factor
Global Warming Baselines Conversion Factors - Joseph Nowarski
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There is no example of direct conversion from 1951-1980 to 1850-1900 baseline for
land only.
IPCC [8] and NASA [4] [5] options apply 2 separate sources of information.
The Berkeley Earth (LBL) [6] option is the favorite option as the conversion factor
was calculated using only one source of data.
The Berkeley Earth (LBL) [6] option +0.49°C is selected and will be applied for
further analysis and conversion of the databases in this work.
Table 22 - Estimation of conversion factor from 1901-2000 to 1850-1900 baseline
according to Berkeley Earth (LBL) [6] [°C]
Ref from to °C
LBL [6] 1901-2000 1850-1900 -0.49
CF 1901-2000 1850-1900 +0.49
Table 23 - Conversion factors to 1850-1900 baseline for land only [°C]
from BL: Land
1850-1900 +0.00
1901-2000 +0.49
1951-1980 +0.49
Conversion Factors for Ocean Only
IPCC 2021 Report [8] p5 item A.1.2 describes the following relations between the
1850-1900 baseline and other periods: “Global surface temperature was 1.09 [0.95
to 1.20] °C higher in 2011–2020 than 1850–1900, with larger increases over land
(1.59 [1.34 to 1.83] °C) than over the ocean (0.88 [0.68 to 1.01] °C)”.
According to the NASA database, the average temperature change for the
ocean only in 2011–2020 was 0.58°C above the 1951-1980 baseline.
According to Berkeley Earth (LBL) [4] [5] "the ocean surface temperature,
excluding sea ice regions, has increased in 2021 0.83 ± 0.05 °C" above the average
temperature from 1850 to 1900.
According to the NASA database, the temperature change of the ocean only in
2021 was 0.56°C above the 1951-1980 baseline.
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Table 24 - Database for ocean only
NASA
Reference [1] [2]
Units °C
Records annual
from 1880
to 2021
years 142
Baseline (BL) 1951-1980
BL years 30
Decimal places 2
Ave in BL +0.0007
Table 25 - Baselines and reference periods
IPCC LBL NASA
Reference [8] [4] [5] [1] [2]
1850-1900 +0.00 +0.00
1901-2000 -0.06
1951-1980 +0.00
2011-2020 +0.88 +0.58
2021 +0.83 +0.56
Table 26 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to reference [8] (IPCC) and NASA database [°C]
Ref from to °C
[8] 1850-1900 2011-2020 +0.88
NASA 1951-1980 2011-2020 +0.58
Δ 1850-1900 1951-1980 +0.31
CF 1951-1980 1850-1900 +0.31
Table 27 - Estimation of conversion factor from 1951-1980 to 1850-1900 baseline
according to reference [4] [5] (LBL) and NASA database [°C]
Ref from to °C
[4] [5] 1850-1900 2021 +0.83
NASA 1951-1980 2021 +0.56
Δ 1850-1900 1951-1980 +0.27
CF 1951-1980 1850-1900 +0.27
Table 28 - All estimations of the conversion factor from 1951-1980 to 1850-1900
baseline for ocean only [°C]
Ref [8] [4] [5] Ave *
°C °C °C
CF +0.31 +0.27 +0.29
* selected conversion factor
Both options apply two sources of information. The selected conversion factor is an
average of both options.
Global Warming Baselines Conversion Factors - Joseph Nowarski
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Table 29 - Estimation of conversion factor from 1901-2000 to 1850-1900 baseline
according to NASA database [°C]
Ref from to °C
CF 1951-1980 1850-1900 +0.29
NASA 1951-1980 1901-2000 -0.06
CF 1901-2000 1850-1900 +0.23
Table 30 - Conversion factors to 1850-1900 baseline for ocean only [°C]
from BL: Ocean
1850-1900 +0.00
1901-2000 +0.23
1951-1980 +0.29
All Conversion Factors of Global Surface Temperature Changes Baselines
Table 31 - Conversion factors to 1850-1900 baseline [°C]
from BL: Land+Ocean Land Ocean
1850-1900 +0.00 +0.00 +0.00
1901-2000 +0.28 +0.49 +0.23
1951-1980 +0.31 +0.49 +0.29
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References
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4. NASA Goddard Institute for Space Studies. Dataset accessed 2022-02-05
at https://data.giss.nasa.gov/gistemp
2. Lenssen, N., G. Schmidt, J. Hansen, M. Menne, A. Persin, R. Ruedy, and D.
Zyss, 2019: Improvements in the GISTEMP uncertainty model. J. Geophys.
Res. Atmos., 124, no. 12, 6307-6326, doi:10.1029/2018JD029522.
3. NOAA National Centers for Environmental information, Climate at a Glance:
Global Time Series, published February 2022, retrieved on March 9, 2022
from https://www.ncdc.noaa.gov/cag/
4. Berkeley Earth - Global Temperature Report for 2021
http://berkeleyearth.org/global-temperature-report-for-2021/
5. Rohde, R. A. and Hausfather, Z.: The Berkeley Earth Land/Ocean
Temperature Record, Earth Syst. Sci. Data, 12, 3469-3479,
https://doi.org/10.5194/essd-12-3469-2020, 2020.
6. Berkeley Earth - Time Series Data, Land Only (1750 – Recent), Monthly
Average Temperature (annual summary)
http://berkeleyearth.org/data/
7. European Commission, Climate Action, EU Action,
Climate strategies & targets, 2050 long-term strategy, 4 March 2020
https://ec.europa.eu/clima/eu-action/climate-strategies-targets/2050-long-
term-strategy_en
8. IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The
Physical Science Basis. Contribution of Working Group I to the Sixth
Assessment Report of the Intergovernmental Panel on Climate Change
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(eds.)]. Cambridge University Press. In Press.
9. Geography - Surface and Air Temperature
https://geography.name/surface-and-air-temperature
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https://www.climate-lab-book.ac.uk/2017/defining-pre-industrial/
11. Global temperature change: where do we start? - Ed HawkinsEd Hawkins,
National Centre for Atmospheric Science
https://composite-indicators.jrc.ec.europa.eu/sites/default/files/03%20-
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