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Water Vapor Feedback in Climate Models



General circulation models (GCMs) are highly sophisticated computer tools for modeling climate change, and they incorporate a large number of physical processes and variables. One of the most important challenges is to properly account for water vapor (clouds and humidity) in climate warming. In his Perspective, Cess discusses results reported in the same issue by Soden et al. in which water vapor feedback effects are tested by studying moistening trends in the upper troposphere. Satellite observations of atmospheric water vapor are found to agree well with moisture predictions generated by one of the key GCMs, showing that these feedback effects are being properly handled in the model, which eliminates a major potential source of uncertainty.
DOI: 10.1126/science.1119258
, 795 (2005);310 Science
Robert D. Cess
Water Vapor Feedback in Climate Models
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lished previously is 5.5 Å. In electron density
maps in that resolution range, nucleic acid
helices look like curved ribbons whose con-
stituent nucleotides are often difficult to
delineate, and protein density is hard to inter-
pret at all. Nevertheless, a great deal was
learned from those electron density maps
because relevant structures that had been
solved at higher resolution before could be
fitted into them. The problem with the 70S
model that emerged is that wherever its
structure deviated from that of the structures
being fit into its electron density maps, it was
difficult to be sure what was going on. In 3.5
Å resolution electron density maps, such as
those that led to the 70S E. coli structure
reported by Schuwirth et al., these ambigui-
ties disappear because individual nucleotides
are clearly visualized, and protein electron
density is independently interpretable.
What has been learned? The structures
presented by Schuwirth et al. are not the last
word about the information contained in the
particular crystals examined. Ribosomal
proteins are not fully modeled at this point,
and the structures are not fully refined.
In addition, the crystals analyzed by
Schuwirth et al. lack transfer RNAs or any
of the other proteins, nucleic acids, or small
molecules that interact with the ribosome
during protein synthesis. Nevertheless, sev-
eral themes clearly emerge. The structures
of the bridges that hold the two subunits
together are clear, which is important
because the bridges are critical function-
ally: The two subunits of the ribosome not
only communicate during protein synthesis,
they also engage in coordinated, relative
motions (8). In addition, the two 70S struc-
tures reported by Schuwirth et al. differ in
the orientation of the head domains of their
small subunits, and in neither is the head
domain position the same as it is in the T.
thermophilus 70S ribosome structure now
available (7). Movements of the small sub-
unit’s head domain like the ones reported by
Schuwirth et al. occur during protein syn-
thesis [e.g., (8)]. It is now possible to under-
stand how these motions occur at the
molecular level, and to propose models for
how they might be coupled to the events of
protein synthesis. It remains to be seen what
the small differences in conformation
between the large ribosomal subunit of
these E. coli ribosomes and the large ribo-
somal subunit structures of other organisms
actually mean. Thus, the ribosome struc-
tures obtained by Schuwirth et al. really do
advance our understanding of protein syn-
thesis. Now that high-quality crystals are
available for the E. coli 70S ribosome, the
rate at which new information is obtained
should increase.
1. B. S. Schuwirth et al., Science 310, 827 (2005).
2. N. Ban, P. Nissen, J. Hansen, P. B. Moore, T. A. Steitz,
Science 289, 905 (2000).
3. J. Harms et al., Cell 107, 679 (2001).
4. B.T. Wimberly et al., Nature 407, 327 (2000).
5. F. Schluenzen et al., Cell 102, 615 (2000).
6. M. Pioletti et al., EMBO J. 20, 1829 (2001).
7. M. M.Yusupov et al., Science 292, 883 (2001).
8. J. Frank, R. K. Agrawal, Nature 406, 318 (2000).
9. J. Cate, personal communication.
eneral circulation models (GCMs)
are the most detailed computer sim-
ulations available for projecting cli-
mate change caused by increasing green-
house gases, as well as other anthropogenic
changes. These numerical models contain
numerous parameterizations of physical
processes occurring within the climate sys-
tem (that is, small-scale processes have to
be described within the models). As a
result, there is a need to devise ways of test-
ing these parameterizations and processes
within GCMs. On page 841 of this issue,
Soden et al. (1) report an important reality
check on one such process: the role of
atmospheric water vapor in climate change.
It has long been known (2) that cloud-
climate interactions constitute a major
uncertainty in attempting to project future
climate change with a GCM. As an illustra-
tive example, if global cloud cover were
to decrease because of climate warming,
then this decrease reduces the infrared
greenhouse effect due to clouds. Thus, the
climate system is able to emit infrared
radiation more efficiently, moderating the
warming and so acting as a negative feed-
back mechanism. But there is a related
positive feedback in this example that
would increase the warming: The solar
radiation absorbed by the climate system
increases because the diminished cloud
cover causes a reduction of reflected solar
radiation by the atmosphere.
The situation is actually far more com-
plicated than in this simple example,
because changes in cloud cover will
undoubtedly depend on cloud type and geo-
graphical location. Moreover, there would
likely be associated changes in cloud alti-
tude and cloud optical depth. One test of
cloud-climate interactions within a GCM is
to determine, relative to satellite observa-
tions, how well a GCM represents the radia-
tive impact of clouds on the model’s climate
during the 5 years encompassing 1985 to
1989, and the top panel of the figure
demonstrates that many models do rather
poorly in this respect. And with regard to
those models that do agree well with Earth
Radiation Budget Satellite observations, it
must be emphasized that this test is a neces-
sary, but not sufficient, test of a model.
Another feedback mechanism is water
vapor feedback. Water vapor is the atmo-
sphere’s dominant greenhouse gas, and a
change in its concentration associated with a
change in climate would alter the greenhouse
effect of the atmosphere, thus producing a
feedback mechanism. In 1967 it was pro-
posed (3) that the atmosphere might conserve
its relative humidity, and if so, this would lead
to a positive feedback because a warmer
atmosphere would contain more water vapor,
thus amplifying the warming. And indeed,
GCMs do tend to conserve global mean
atmospheric relative humidity, as is shown
for one such model in the bottom panel of the
figure. But for more than a decade there has
been considerable debate on this issue, with
suggestions that water vapor feedback might
actually be a negative feedback mechanism.
Soden et al. (1) present a very clever
way of testing one aspect of water vapor
feedback. As they point out, observed mois-
tening trends in the lower troposphere have
been linked to corresponding changes in
surface temperature. But attempts to
observe a moistening trend in the upper tro-
posphere have proven to be unsuccessful,
and this is the issue that Soden et al.
address. They accomplish this by using
clear-sky satellite radiance measurements
from the High Resolution Infrared
Radiometer Sounder channel centered at
6.7 µm (channel 12), which measures a por-
tion of the 6.3-µm water vapor absorption
band and therefore is sensitive to water
vapor in the upper troposphere. They then
compare the channel 12 observations of
global mean blackbody temperature, for the
Water Vapor Feedback
in Climate Models
Robert D. Cess
The author is at the Institute for Terrestrial and
Planetary Atmospheres, Marine Sciences Research
Center, State University of New York, Stony Brook, NY
11794, USA. E-mail: SCIENCE VOL 310 4 NOVEMBER 2005
Published by AAAS
on February 17, 2011www.sciencemag.orgDownloaded from
period January 1982 to December 2004, to
those computed from the temperature and
moisture profiles of the Geophysical Fluid
Dynamics Laboratory atmospheric GCM,
which uses prescribed sea surface tempera-
tures. The temporal trends of the observed
and modeled channel 12 observations are in
very good agreement, and this agreement
persists when the GCM
results are repeated
with the assumption of
constant atmospheric
relative humidity. On
the other hand, there is
considerable disagree-
ment with the channel
12 observations when
the GCM results are
repeated by assuming
no change in the water
vapor content of the
upper troposphere. Soden et al. then use
additional satellite observations to empha-
size that global mean relative humidity is
being conserved by the upper troposphere
in response to atmospheric warming.
This work by Soden et al. provides the
clearest evidence yet that GCMs are prop-
erly representing water vapor feedback.
This is an important contribution because it
eliminates one potential uncertainty within
these climate models. There remains, how-
ever, an uncertainty in other climate feed-
back mechanisms, the most notable of
which is cloud feedback as described above.
The reduction of these uncertainties will
require a suite of cleverly designed neces-
sary, but not sufficient, tests of the models.
1. B. J. Soden, D. L. Jackson, V. Ramaswamy, M. D.
Schwarzkopf, X. Huang, Science 310, 841 (2005);
October 2005 (10.1126/science.1115602).
2. R. D. Cess et al., Science 245, 513 (1989).
3. S. Manabe, R. T. Wetherald, J. Atmos. Sci. 24, 241
4. E. F. Harrison et al., J.Geophys. Res.95, 18687 (1990).
5. G. L. Potter, R. D. Cess, J. Geophys. Res. 109, D02106
6. A. Dai et al., J.Clim. 14, 485 (2001).
ond order and the division of chemical
bonding into single or multiple bonds
are among the most fundamental con-
cepts in molecular chemistry. Elements in
the main group of the periodic table may
have up to three bonds to the same bonding
partner (that is, the maximum bond order
can only be three). It was long believed that
this is the highest bond order that can be
achieved in a stable molecule. Because of
this conventional wisdom, the 1964 report
by Cotton et al. (1) on the synthesis of a
molecule with bond order four caused a
sensation. The analysis of transition metal
salt compounds containing the anion
revealed a quadruple bond
between the rhenium atoms. This finding
opened the door to a new field of chemistry
and led to the synthesis of a large number of
hitherto unknown molecules with multiple
bonds having bond orders up to four
between transition metal atoms (2). It has
been speculated that a further extension to
bond order five should in principle be pos-
sible, but attempts to make a compound
with a quintuple bond have been unsuccess-
ful until now. On page 844 of this issue,
Nguyen et al. (3) report the synthesis of a
stable compound with fivefold bonding
between two chromium atoms (see first fig-
ure on the following page).
Chemical bonding between two atoms
is usually discussed in terms of bonding
and antibonding combinations of the
valence atomic orbitals (AOs) that yield
molecular orbitals (MOs). The pivotal AOs
of the transition metal atoms are the five d
orbitals. The figure shows schematically
the combination of the d-AOs that give five
components for the bonding MOs (σ, π, δ)
and five components for the antibonding
MOs (σ*, π*, δ*). The diagram also quali-
tatively indicates the expected ordering for
the energy levels of the orbitals. A quintu-
ple bond between two transition metals
requires that 10 electrons occupy the
lowest lying MOs. This yields one σ bond,
one degenerate π bond, and one degen-
erate δ bond (that is, the π and σ bonds
each have two levels with the same
energy). Transition metal compounds like
with a quadruple bond have
only one (not degenerate) δ bond.
Theoretical analysis (1) showed that the
AOs that form the second component
of the δ bond (see the figure) interact pri-
marily with ligand orbitals such as the
chlorine AOs in [Re
. All previous
attempts to synthesize a molecule with the
general formula L
(where L is
ligand, TM is transition metal) in which the
AOs of TM engage in the “missing”
fifth metal-metal bonding rather than in
TM-L bonding have failed.
Building a Quintuple Bond
Gernot Frenking
1 3 5 7 9 11 13 15 17 19
60°N to 60°S means
Net CRF (W/m
Measured CRF
0 10 20 30 40 50 60 70 80
Relative humidity (%)
Pressure (mbar)
Cloudy predictions. (Top) Actual effect of clouds on climate (measured CRF)
compared to the effect predicted by 19 global climate models. Some of the
models significantly overestimate cloud-induced cooling. Clouds can poten-
tially cool climate (by reflecting solar radiation) and simultaneously heat the
system (by increasing the atmospheric greenhouse effect).The net effect illus-
trated in the figure is cooling, as indicated by the negative values of CRF. Actual
net CRF (cloud-radiative forcing), measured by the Earth Radiation Budget
Satellite (4) and averaged from 60°N to 60°S, is –22 W/m
.(Bottom) Average
relation between atmospheric pressure and humidity for a 120-year (1870 to
1989) simulation of global warming. The profile is an average of 120 annual
mean profiles; the bars represent two standard deviations, indicating that
global mean atmospheric relative humidity is conserved over the entire 120-
year period. The simulation is from the National Center for Atmospheric
Research Community Climate System Model Version 1 (6).
The author is at the Fachbereich Chemie, Philipps-
Universität Marburg, Hans-Meerwein-Strasse, D-
35039 Marburg, Germany. E-mail: frenking
Published by AAAS
on February 17, 2011www.sciencemag.orgDownloaded from
... Although the proportion of water vapor content in the atmosphere is small (0.1-3%), it is the most active element in the atmospheric circulation and Earth climate system [2,3]. The most direct impact of global warming is the change of water vapor content, with warmer temperature increasing water vapor in the atmosphere [4]. ...
Full-text available
Water vapor content plays an important role in climate change and the ecosystem in the Tibetan Plateau (TP) through its complicated interaction with the meteorological elements. However, due to the complex topography of the Tibetan Plateau, it is unreliable to attempt to understand the variation pattern of water vapor content using only observational data. Satellite and reanalysis data can be a good substitute for observational data, but their accuracy still needs to be evaluated. Therefore, based on radiosonde stations data, comprehensive assessment of water vapor content on the TP and surrounding areas derived from ERA-5, Second Modern-Era Retrospective analysis for Research and Applications (MERRA2), Atmospheric Infrared Sounder (AIRS)-only, and weighted ensemble data was performed in the context of spatial and temporal distribution at the annual and seasonal scale. Based on precipitation from Gauge V3.0 and Tropical Rainfall Measuring Mission satellite (TRMM) and temperature from ERA-5, the relationship between water vapor content and temperature and precipitation was analyzed. The results show that water vapor content decreases from southeast to northwest, and ERA-5, MERRA2, and AIRS-only can reasonably reproduce the spatial distribution of annual and seasonal water vapor content, with ERA-5 being more reliable in reproducing the spatial distribution. Over the past 50 years, the water vapor content has shown a gradual increasing trend. The variation trends of AIRS-only, MERRA2, ERA-5, and weighted ensemble data are almost consistent with the radiosonde stations data, with MERRA2 being more reliable in capturing water vapor content over time. Weighted ensemble data is more capable of capturing water vapor content characteristics than simple unweighted products. The empirical orthogonal function (EOF) analysis shows that the first spatial mode values of water vapor content and temperature are positive over the TP, while the values of precipitation present a “negative-positive-negative” distribution from south to north over the TP. In the second spatial mode of EOF analysis, the values of water vapor content, air temperature, and precipitation are all negative. The first temporal modes of EOF analysis, water vapor content, air temperature, and precipitation all show an increasing trend. In conclusion, there is a clear relationship of water vapor content with temperature and precipitation.
... There was generally more precipitation in the southern part of the TP and less precipitation in the northern part. Cess 16 and Xie 17 concluded that there is a positive feedback effect between air temperature and water vapor content on the TP. Li et al. 18 studied the relationship between atmospheric water vapor content and temperature and precipitation in Changchun, and found that water vapor content had a signi cant correlation with temperature, while the trend and amplitude of precipitation and water vapor content variation were not consistent. ...
Full-text available
Based on radiosonde stations and V3.0 data, Atmospheric Infrared Sounder (AIRS)-only, Tropical Rainfall Measuring Mission satellite (TRMM) and MERRA2, and ERA-5 data, we evaluated the ability of each dataset to reproduce water vapor content and explored its relationship with precipitation and temperature over the Tibetan Plateau and its surroundings. The results showed that the southern part of the surrounding area had high water vapor content and a low water vapor content zone appeared in the inner part of the Tibetan Plateau. The largest water vapor content appeared in summer and the smallest in winter. Most of the products could capture the spatial distribution of water vapor content, ERA-5 had the smallest bias and the highest correlation coefficient with the radiosonde data. The water vapor content has shown a gradually increasing trend over the last 50 years, with the most obvious increase in summer. Several sets of products had the same fluctuation trend and value is greater than the radiosonde data. There was a significant positive correlation between air temperature and water vapor content in the Tibetan Plateau, especially in the south. As the latitude increased, the correlation between precipitation and water vapor content gradually decreased and a negative correlation appeared.
... For example, higher air temperature due to increased greenhouse gases by human activity is associated with more atmospheric water vapour. Since this is also a greenhouse gas, its increase provides a positive radiative feedback (Cess, 2005), which can about triple the sensitivity of surface temperature to greenhouse gas forcing according to projections with climate models (Held and Soden, 2000). Moreover, in the projections, tropical tropospheric warming increases with height from the surface as the lapse rates decrease (Ma et al., 2012). ...
Climate feedbacks have been usually estimated using changes in radiative effects associated with increased global-mean surface temperature. Feedback uncertainties, however, are not only functions of global-mean surface temperature increase. In projections by global climate models, it has been demonstrated that the geographical variation of sea surface temperature change brings significant uncertainties into atmospheric circulation and precipitation responses at regional scales. Here we show that the spatial pattern of surface warming is a major contributor to uncertainty in the combined water vapour-lapse rate feedback. This is demonstrated by computing the global-mean radiative effects of changes in air temperature and relative humidity simulated by 31 climate models using a methodology based on radiative kernels. Our results highlight the important contribution of regional climate change to the uncertainty in climate feedbacks, and identify the regions of the world where constraining surface warming patterns would be most effective for higher skill of climate projections.
... For example, higher air temperature due to increased greenhouse gases by human activity is associated with more atmospheric water vapour. Since this is also a greenhouse gas, its increase provides a positive radiative feedback (Cess, 2005), which can about triple the sensitivity of surface temperature to greenhouse gas forcing according to projections with climate models (Held and Soden, 2000). Moreover, in the projections, tropical tropospheric warming increases with height from the surface as the lapse rates decrease (Ma et al., 2012). ...
... The sum of feedbacks are negative, dominated by the increased LW emission as blackbody emission temperature rises. Water vapor feedbacks are positive (Cess, 2005;Held & Soden, 2000) and coupled to a negative lapse-rate feedback (a warmer atmosphere with more water vapor has a higher emission level; Folkins, 2002). Surface albedo feedbacks (Colman, 2013) result from changing surface albedo (mostly from ice and snow) in a warmer (or cooler) climate. ...
Full-text available
The Community Earth System Model Version 2 (CESM2) has an equilibrium climate sensitivity (ECS) of 5.3 K. ECS is an emergent property of both climate feedbacks and aerosol forcing. The increase in ECS over the previous version (CESM1) is the result of cloud feedbacks. Interim versions of CESM2 had a land model that damped ECS. Part of the ECS change results from evolving the model configuration to reproduce the long‐term trend of global and regional surface temperature over the twentieth century in response to climate forcings. Changes made to reduce sensitivity to aerosols also impacted cloud feedbacks, which significantly influence ECS. CESM2 simulations compare very well to observations of present climate. It is critical to understand whether the high ECS, outside the best estimate range of 1.5–4.5 K, is plausible.
... Held and Soden 2000;Cess 2005;Rapp 2012). Within the Midwest Corn Belt, over half of the stations experienced an increase !0.89 C (1.6 F), which tested significant at the 99 percent confidence level (a ¼ 0.01) with the Upper Midwest stations again dominating. ...
Full-text available
Agricultural land use changes have likely played an important role in modifying local and regional climate factors. According to a recent study, summers in the Midwest were significantly cooler and wetter due to the dramatic increases in production of corn and soybeans caused by an intensification of agricultural practices (Alter et al. 2018). In this context, this study examines regional changes manifested in multiple climate variables and directly quantifies the magnitude of potential moisture contributions from Midwest corn and soybean agriculture. Meteorological data were collected for daily minimum, maximum, and dewpoint temperatures over a sixty-one-year study period from fifty-nine National Weather Service first-order stations and cooperative network stations. Regional growing season climatology for two study regions that focused on the rain-fed Midwest Corn Belt and the southern United States extending to the Gulf Coast was analyzed. Further, vapor pressure deficit was calculated to ascertain any regional changes. Field surveys of corn and soybean crop transpiration were used in a multivariate model to estimate lower atmospheric moisture contributions at midday during peak season directly from intensified rain-fed agriculture. Findings indicate an increase in regional dewpoint, associated with elevated nocturnal minimums and suppression of both daily maximum and vapor pressure deficit, concentrated in the Midwest Corn Belt, which was not evident within the South. The estimation results of the atmospheric moisture contributions from the Corn Belt confirm the intensification of Midwestern agriculture as a regional climate modifier. Key Words: agriculture, dewpoint, energy balance, humidity, regional climate.
... Modeling climate in a probabilistic manner would allow for accurate risk assessment and planning of infrastructure. To reduce the uncertainty associated with conclusions drawn from GCM results, improved spatial resolution and temporal extents of observed data are required, and a better processlevel understanding of complex feedbacks such as atmospheric water vapor (the atmosphere's dominant greenhouse gas) and changes in cloudiness, cloud type and properties, and snow cover (Cess 2005). This is an ongoing issue: for instance, it has recently been suggested that this feedback is, in fact, negative; Soden et al. (2005) refute this, using remote sensing bands to confirm that RH is preserved in the upper troposphere, in accordance with GCM-modeling practice, and thereby resolving the modeling uncertainty regarding the water vapor feedback. ...
... Especially the case of atmospheric water vapor, it's not only a water body that condenses the rainfall but also a greenhouse gas with the release of latent heat to influence the atmospheric circulation patterns. Study on the hydrological cycle, the atmospheric water vapor transport has drawn more and more attention as its importance to drought and flood and sensitivity to anthropogenic effects [2][3][4]. ...
Full-text available
Using the observational and JRA-25 reanalysis datasets, three dimensional structure of water vapor transportation and its relationships with the summer flood/drought situations are investigated in summer time over the Huaihe River Basin (HRB) in eastern China. Results show that there exist major net water vapor input from the western and southern boundaries and net water vapor output in the eastern and northern ones. The water vapor transported from the Bay of Bengal and the South China Sea regions are critical to the precipitation in the HRB region. A typical flood has close relationships with positive anomaly of the transported water vapor from the Bay of Bengal. For a typical drought year, water vapor transported from the Bay of Bengal, as well as the South China Sea, are greatly reduced. And the contribution of the South China Sea is relatively large. Water vapor transported by the tropical westerly also plays a key role in the summer precipitation of the HRB area. Results suggested that the region of the southeast of the Tibet Plateau plays a key role as "transfer post".
Total column H 2 O is measured by two remote sensing techniques at the Altzomoni Atmospheric Observatory (19° 12'N, 98° 65'W, 4000 m a.s.l.), a high-altitude, tropical background site in central Mexico. A ground-based solar absorption FTIR spectrometer that is part of the Network for Detection of Atmospheric Composition Change (NDACC) is used to retrieve water vapor in three spectral regions (6074-6471, 2925-2941 and 1110-1253 cm ⁻¹ ) and is compared to data obtained from a GPS (Global Positioning System) receiver that is part of the TLALOCNet GPS-meteorological network. Strong correlations are obtained between the coincident hourly means from the three FTIR products and small relative bias and correction factors could be determined for each when compared to the more consistent GPS data. Retrievals from the 2925-2941 cm ⁻¹ spectral region have the highest correlation with GPS (R ² = 0.998, std= 0.18 cm (78.39%), mean diff= 0.04 cm (8.33%)), although the other products are also highly correlated (R ² = >0.99, std= <0.20 cm (< 90%), mean diff= < 0.1 cm (< 24%)). Clear-sky, dry bias (CSDB) values are reduced to <10% (< 0.20 cm) when coincident hourly means are used in the comparison. The use of GPS and FTIR water vapor products simultaneously leads to a more complete and better description of the diurnal and seasonal cycles of water vapor. We describe the water vapor climatology with both complementary data sets, nevertheless, pointing out the importance of considering the clearsky dry bias arising from the large diurnal and seasonal variability of water vapor at this high-altitude tropical site.
Water vapor is a greenhouse gas that dominates Earth’s terrestrial radiation absorption. As the planetary temperature warms, forced by increasing CO2 and other greenhouse gases, water vapor content of the atmosphere increases, thereby producing the strongest positive feedback in the climate system. At the same time, the rate at which atmospheric temperature drops with height (the “lapse rate”) is expected to decrease with warming. This represents a smaller, but significant, negative feedback since it enables the planet to radiate more effectively to space. The two feedbacks are closely coupled to each other, and the combined result represents the foundational net positive feedback in the climate system, mandating substantial global warming in response to increased greenhouse gases. This review summarizes the published work that has provided an ever deepening understanding of these critical feedbacks. The historical context, beginning with the 19th century awakening to the importance of water vapor in the climate, is outlined before the review’s focus shifts to the theoretical, observational, and modeling work in recent decades that has transformed our understanding of the feedbacks’ role in climate change. It is shown that the evidence is now overwhelming that combined water vapor and lapse rate processes indeed provide the strongest positive feedback in the climate system. However, important challenges remain. This review provides physicists with a deeper understanding of these feedbacks and stimulates engagement with the climate research community. Together the scientific community can facilitate further rigor, understanding, and confidence in these most fundamental Earth system processes.
Full-text available
The small ribosomal subunit is responsible for the decoding of genetic information and plays a key role in the initiation of protein synthesis. We analyzed by X-ray crystallography the structures of three different complexes of the small ribosomal subunit of Thermus thermophilus with the A-site inhibitor tetracycline, the universal initiation inhibitor edeine and the C-terminal domain of the translation initiation factor IF3. The crystal structure analysis of the complex with tetracycline revealed the functionally important site responsible for the blockage of the A-site. Five additional tetracycline sites resolve most of the controversial biochemical data on the location of tetracycline. The interaction of edeine with the small subunit indicates its role in inhibiting initiation and shows its involvement with P-site tRNA. The location of the C-terminal domain of IF3, at the solvent side of the platform, sheds light on the formation of the initiation complex, and implies that the anti-association activity of IF3 is due to its influence on the conformational dynamics of the small ribosomal subunit.
Full-text available
Radiative convective equilibrium of the atmosphere with a given distribution of relative humidity is computed as the asymptotic state of an initial value problem.The results show that it takes almost twice as long to reach the state of radiative convective equilibrium for the atmosphere with a given distribution of relative humidity than for the atmosphere with a given distribution of absolute humidity.Also, the surface equilibrium temperature of the former is almost twice as sensitive to change of various factors such as solar constant, CO2 content, O3 content, and cloudiness, than that of the latter, due to the adjustment of water vapor content to the temperature variation of the atmosphere.According to our estimate, a doubling of the CO2 content in the atmosphere has the effect of raising the temperature of the atmosphere (whose relative humidity is fixed) by about 2C. Our model does not have the extreme sensitivity of atmospheric temperature to changes of CO2 content which was adduced by Möller.
Full-text available
The impact of clouds on the earth's radiation balance is assessed in terms of longwave, shortwave, and net cloud forcing by using monthly averaged clear-sky and cloudy-sky flux data derived from the NASA Earth Radiation Budget Experiment (ERBE). Emphasis is placed on regional measurements, regional cloud forcing, zonal cloud forcing, and snow and ice contributions. It is shown that the global mean cooling varied from 14 to 21 W/sq m between April 1985 and January 1986; hemispherically, the longwave and shortwave cloud forcing nearly cancel each other in the winter hemisphere, while in the summer the negative shortwave cloud forcing is significantly lower than the longwave cloud forcing, producing a strong cooling. The ERBE data reveal that globally, hemispherically, and zonally, clouds have a significant effect on the radiative heating gradients.
Full-text available
The small ribosomal subunit performs the decoding of genetic information during translation. The structure of that from Thermus thermophilus shows that the decoding center, which positions mRNA and three tRNAs, is constructed entirely of RNA. The entrance to the mRNA channel will encircle the message when a latch-like contact closes and contributes to processivity and fidelity. Extended RNA helical elements that run longitudinally through the body transmit structural changes, correlating events at the particle's far end with the cycle of mRNA translocation at the decoding region. 96% of the nucleotides were traced and the main fold of all proteins was determined. The latter are either peripheral or appear to serve as linkers. Some may assist the directionality of translocation.
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Genetic information encoded in messenger RNA is translated into protein by the ribosome, which is a large nucleoprotein complex comprising two subunits, denoted 30S and 50S in bacteria. Here we report the crystal structure of the 30S subunit from Thermus thermophilus, refined to 3 A resolution. The final atomic model rationalizes over four decades of biochemical data on the ribosome, and provides a wealth of information about RNA and protein structure, protein-RNA interactions and ribosome assembly. It is also a structural basis for analysis of the functions of the 30S subunit, such as decoding, and for understanding the action of antibiotics. The structure will facilitate the interpretation in molecular terms of lower resolution structural data on several functional states of the ribosome from electron microscopy and crystallography.
ABSTRACT The Climate System Model, a coupled global climate model without ‘‘flux adjustments’’ recently developed at the National Center for Atmospheric Research, was used to simulate the twentieth-century climate using historical greenhouse,gas and sulfate aerosol forcing. This simulation was,extended,through the twenty-first century under two newly developed scenarios, a business-as-usual case (ACACIA-BAU, CO2 710 ppmv in 2100) and a CO2 stabilization case (STA550, CO 2 540 ppmv in 2100). Here we compare the simulated and observed twentieth-century climate, and then describe the simulated climates for the twenty-first century. The model,simulates the spatial and temporal,variations of the twentieth-century climate reasonably well. These include the rapid rise in global and zonal mean surface temperatures since the late 1970s, the precipitation increases over northern mid- and high-latitude land areas, ENSO-induced precipitation anomalies, and Pole‐ midlatitude oscillations (such as the North Atlantic oscillation) in sea level pressure fields. The model,has a cold bias (28‐68C) in surface air temperature over land, overestimates of cloudiness (by 10%‐30%) over land, and underestimates,of marine stratus clouds to the west of North and South America and Africa. The projected global surface warming,from the 1990s to the 2090s is ;1.98C under the BAU scenario and ;1.58C under the STA550 scenario. In both cases, the midstratosphere cools due to the increase in CO 2, whereas the lower stratosphere warms in response to recovery of the ozone layer. As in other coupled models, the surface warming,is largest at winter high latitudes ($5.08C from the 1990s to the 2090s) and smallest (;1.08C) over the southern oceans, and is larger over land areas than ocean areas. Globally averaged precipitation increases by ;3.5% (3.0%) from the 1990s to the 2090s in the BAU (STA550) case. In the BAU case, large precipitation increases (up to 50%) occur over northern mid- and high latitudes and over India and the Arabian Peninsula. Marked differences occur between,the BAU and STA550 regional precipitation changes resulting from inter- decadal variability. Surface evaporation increases at all latitudes except for 60 8‐908S. Water vapor from increased tropical evaporation is transported into mid- and high latitudes and returned to the surface through increased precipitation there. Changes in soil moisture content are small (within 63%). Total cloud cover changes little, although there is an upward,shift of midlevel clouds. Surface diurnal temperature range decreases by about 0.28‐ 0.58C over most land areas. The 2‐8-day synoptic storm activity decreases (by up to 10%) at low latitudes and over midlatitude oceans, but increases over Eurasia and Canada. The cores of subtropical jets move slightly up- and equatorward. Associated with reduced latitudinal temperature gradients over mid- and high latitudes, the wintertime Ferrel cell weakens (by 10%‐15%). The Hadley circulation also weakens (by ;10%), partly due to
1] We compare cloud-radiative forcing (CRF) at the top-of-the atmosphere from 19 atmospheric general circulation models, employing simulations with prescribed sea-surface temperatures, to observations from the Earth Radiation Budget Experiment (ERBE). With respect to 60°N to 60°S means, a surprising result is that many of the 19 models produce unusually large biases in Net CRF that are all of the same sign (negative), meaning that many of the models significantly overestimate cloud radiative cooling. The primary focus of this study, however, is to demonstrate a diagnostic procedure, using ERBE data, to test if a model might produce, for a given region, reasonable CRF as a consequence of compensating errors caused either by unrealistic cloud vertical structure, cloud optical depth or cloud fraction. For this purpose we have chosen two regions, one in the western tropical Pacific characterized by high clouds spanning the range from thin cirrus to deep convective clouds, and the other in the southeastern Pacific characterized by trade cumulus. For a subset of eight models, it is found that most typically produce more realistic regionally-averaged CRF (and its longwave and shortwave components) for the southeastern region as opposed to the western region. However, when the diagnostic procedure for investigating cloud vertical structure and cloud optical depth is imposed, this somewhat better agreement in the southeastern region is found to be the result of compensating errors in either cloud vertical structure, cloud optical depth or cloud fraction. The comparison with ERBE data also shows large errors in clear-sky fluxes for many of the models.
We describe the high resolution structure of the large ribosomal subunit from Deinococcus radiodurans (D50S), a gram-positive mesophile suitable for binding of antibiotics and functionally relevant ligands. The over-all structure of D50S is similar to that from the archae bacterium Haloarcula marismortui (H50S); however, a detailed comparison revealed significant differences, for example, in the orientation of nucleotides in peptidyl transferase center and in the structures of many ribosomal proteins. Analysis of ribosomal features involved in dynamic aspects of protein biosynthesis that are partially or fully disordered in H50S revealed the conformations of intersubunit bridges in unbound subunits, suggesting how they may change upon subunit association and how movements of the L1-stalk may facilitate the exit of tRNA.
Climate models predict that the concentration of water vapor in the upper troposphere could double by the end of the century as a result of increases in greenhouse gases. Such moistening plays a key role in amplifying the rate at which the climate warms in response to anthropogenic activities, but has been difficult to detect because of deficiencies in conventional observing systems. We use satellite measurements to highlight a distinct radiative signature of upper tropospheric moistening over the period 1982 to 2004. The observed moistening is accurately captured by climate model simulations and lends further credence to model projections of future global warming.
In his Perspective, Moore discusses the atomic-resolution structure that has been obtained by Schuwirth et al. for the Escherichia coli ribosome, the enzyme responsible for protein synthesis in that organism. The vast body of biochemical and genetic data obtained for this particle over the past half century can now be interpreted structurally.