New computer model claims global warming decreases clouds

A new paper published in Nature claims global warming reduces low clouds, the opposite of what has been claimed in the past. For example, the forthcoming IPCC AR5 notes climate models have predicted that in a warmer climate, increased evaporation will increase low cloud thickness, vertical, and horizontal extent, all of which increases reflection of sunlight [albedo], cools the planet, and acts as a negative feedback.

"The modelled response of low clouds does not appear to be dominated by a single feedback mechanism, but rather the net effect of several potentially competing mechanisms as elucidated in LES and GCM sensitivity studies (e.g., Zhang and Bretherton, 2008; Blossey et al., 2013; Bretherton et al., 2013). Starting with some proposed negative feedback mechanisms, it has been argued that in a warmer climate, low clouds will be: (i) horizontally more extensive, because changes in the lapse rate of temperature also modify the lower tropospheric stability (Miller, 1997); (ii) optically thicker, because adiabatic ascent is accompanied by a larger condensation rate (Somerville and Remer, 1984); and (iii) vertically more extensive, in response to a weakening of the tropical overturning circulation (Caldwell and Bretherton, 2009)." - AR5 draft pg 7-20

The authors base the claim upon their computer model which allegedly overturns the prior 'settled science' on clouds and thereby proclaims the globe will warm 4C by 2100. 

"They report in Nature that updraughts of water vapour can rise 15 kms to form high clouds that produce heavy rains, or the vapour can rise just a few kilometers before coming back to the surface without forming rain clouds. When this happens the process actually reduces the overall cloud cover because it dessicates the clouds above: it draws away water vapour from the higher regions in a process called convective mixing. [see New paper finds IPCC climate models don't realistically simulate convection and thus convective mixing] 

Climate models in the past have tended to predict high cloud formation that damps warming. [No - models have predicted the opposite: that high clouds increase the 'greenhouse' effect and increase warming] What Sherwood and his colleagues have done is demonstrate that the world may not work like that."

Prior posts on clouds and water vapor as negative feedbacks which cool the planet

Warming climate may cut cloud cover

December 31, 2013 in Clouds, Temperature Increase, Warming

FOR IMMEDIATE RELEASE

In a warmer world there may be fewer clouds – and less of a cooling effect
Image: Fir0002 at English Wikipedia

By Tim Radford

One of the great unknowns of climate science is what effect clouds have in accelerating or slowing warming. A new study sheds a disturbing light on their possible impact.

LONDON, 31 December – Australian and French scientists believe they have cracked one of the great puzzles of climate change and arrived at a more accurate prediction of future temperatures.

The news is not good, according to Steven Sherwood of Australia’s Centre for Excellence for Climate System Science at the University of New South Wales. If carbon emissions are not reduced, then by 2100 the world will have warmed by 4°C.

This figure does not, at first, sound high: researchers have been warning for 20 years on the basis of computer models that under the notorious business-as-usual scenario in which everybody goes on burning coal and oil, then as carbon dioxide levels double, global temperatures could rise by between 1.5°C and 4.5°C.

Pessimists could cite one extreme, optimists the other: the range of uncertainty was a recognition that there were still some big unknowns in the machinery of climate, and one of those unknowns was the behaviour of the clouds in a warmer world.

More warmth means more evaporation, more vapour could mean more clouds. Low-level clouds reflect sunlight back into space, and help cool the climate a bit. This is what engineers call negative feedback.

Drying the clouds

But if more water vapour actually led to less cloud, then more sunlight would reach the surface and the world would warm even more: positive feedback would be in play. Climate models cater for such possibilities, but cannot choose between them.

What Sherwood and his colleagues from Pierre and Marie Curie University in Paris did was to start with some real-world observations of what happens when water vapour gets into the atmosphere.

They report in Nature that updraughts of water vapour can rise 15 kms to form high clouds that produce heavy rains, or the vapour can rise just a few kilometers before coming back to the surface without forming rain clouds.

When this happens the process actually reduces the overall cloud cover because it dessicates the clouds above: it draws away water vapour from the higher regions in a process called convective mixing.

Climate models in the past have tended to predict high cloud formation that damps warming. [say what? models have predicted the opposite: that high clouds increase the 'greenhouse' effect and increase warming] What Sherwood and his colleagues have done is demonstrate that the world may not work like that.

Profound effects in prospect

So the next step was to feed the new understanding into computer simulations. These then showed that climate cycles could develop that would take vapour to a wider range of heights in the atmosphere, with the consequence that fewer clouds would form as climate warms.

If so – and other climate scientists will have their own arguments with the findings – then as carbon dioxide levels double, which they will do in the next 50 years or so, the average planetary temperatures will increase by a colossal 4°C.

Governments have expressed the wish – but not so far taken the necessary action – to contain planetary temperatures to a rise of no more than 2°C. If Sherwood and colleagues are right, they will not get their wish. And the process will go on. The temperatures will continue to soar beyond 2100, to reach an additional 8°C by 2200.

“Climate skeptics like to criticise climate models for getting things wrong, and we are the first to admit they are not perfect, but what we are finding is that the mistakes are being made by those models that predict less warming, not those that predict more”, said Professor Sherwood.

“Rises in global average temperatures of this magnitude will have profound impacts on the world and the economies of many countries if we don’t urgently curb our emissions.” – Climate News Network

Spread in model climate sensitivity traced to atmospheric convective mixing

• Steven C. Sherwood,
• Sandrine Bony
• & Jean-Louis Dufresne

• Affiliations
• Contributions
• Corresponding author

Nature

 

505,

 

37–42

 

(02 January 2014)

 

doi:10.1038/nature12829

Received

 

16 May 2013 

Accepted

 

05 November 2013 

Published online

 

01 January 2014

Article tools

Abstract

• Abstract• 
• References• 
• Author information• 
• Extended data figures and tables• 
• Comments

Equilibrium climate sensitivity refers to the ultimate change in global mean temperature in response to a change in external forcing. Despite decades of research attempting to narrow uncertainties, equilibrium climate sensitivity estimates from climate models still span roughly 1.5 to 5 degrees Celsius for a doubling of atmospheric carbon dioxide concentration, precluding accurate projections of future climate. The spread arises largely from differences in the feedback from low clouds, for reasons not yet understood. Here we show that differences in the simulated strength of convective mixing between the lower and middle tropical troposphere explain about half of the variance in climate sensitivity estimated by 43 climate models. The apparent mechanism is that such mixing dehydrates the low-cloud layer at a rate that increases as the climate warms, and this rate of increase depends on the initial mixing strength, linking the mixing to cloud feedback. The mixing inferred from observations appears to be sufficiently strong to imply a climate sensitivity of more than 3 degrees for a doubling of carbon dioxide. This is significantly higher than the currently accepted lower bound of 1.5 degrees, thereby constraining model projections towards relatively severe future warming.

Paper shows climate models underestimate cooling effect from clouds by a factor of 4

A paper published in the technical newsletter of the Global Energy and Water Cycle Experiment finds that climate models suppress the negative feedback from low clouds, which serve to cool the Earth by reflection of incoming sunlight. The paper notes that cloud feedbacks in computer models are not only uncertain in magnitude, but even in sign (positive or negative). As climate scientist Dr. Roy Spencer has pointed out, a mere 1 to 2% natural variation in cloud cover can alone account for whether there is global warming or global cooling, despite any alleged effects of CO2.

Using satellite observations, the paper shows that the feedback from low clouds is indeed negative and is underestimated in climate models by a factor of four. This has the effect of the models greatly overestimating global warming from CO2 and underestimating the influence of variations of the Sun/cosmic rays via cloud formation.

Is There a Missing Low Cloud Feedback in Current Climate Models? 

Graeme L. Stephens
Department of Atmospheric Science, Colorado State University, Boulder, Colorado, USA 

Radiative feedbacks involving low level clouds are a primary cause of uncertainty in global climate model projections. The feedback in models is not only uncertain in magnitude, but even its sign varies across climate models (e.g., Bony and Dufresne, 2005). These low cloud feedbacks have been hypothesized in terms of the effects of two primary cloud variables—low cloud amount and cloud optical depth. The basis of these feedbacks relies on the connection between these variables and the solar radiation leaving the planet exemplified in the following simple expressions  (Stephens, 2005). ...an increase in optical depth with an increase in temperature results in an increase in cloud albedo, suggesting a negative feedback.
...
The net consequence of these biases is that the optical depth of low clouds in GCMs (General Circulation Models) is more than a factor of two greater than observed, resulting in albedos of clouds that are too high. This model low-cloud albedo bias is not a new finding and is not a feature of just these two models. The study of Allan et al. (2007), for example, also noted how the reflection by low-level clouds in the unified model of the UK Meteorological Office is significantly larger than matched satellite observations of albedo, suggesting that this bias also exists in that model. The mean LWP (cloud liquid water path) of model clouds that contributed to this in the most recent Intergovernmental Panel on Climate Change assessment is close to 200 g/m2, which is also nearly a factor of two larger than observed. 

The implication of this optical depth bias that owes its source to biases in both the LWP and particle sizes is that the solar radiation reflected by low clouds is significantly enhanced in models compared to real clouds. This reflected sunlight bias has significant implications for the cloud-climate feedback problem.  The  consequence is  that   this  bias  artificially suppresses the low cloud optical depth feedback in models by almost a factor of four and thus its potential role as a negative feedback. This bias explains why the optical depth feedback is practically negligible in most global models (e.g., Colman et al., 2003) and why it has received scant attention in low cloud feedback discussion. These results are also relevant to the model biases in absorbed solar radiation discussed recently by Trenberth and Fasullo (2010) and as explored in more detail in Stephens et al. (2010).

Analysis finds global warming of 20th century entirely explained by changes in solar activity and clouds

A new analysis from the German EIKE site finds the global warming of the 20th century is entirely explainable on the basis of a sustained increase of solar activity, modulated by changes in cloud cover induced by cosmic rays and an enormous amount of cloud condensation nuclei blasted into the atmosphere from the nuclear tests conducted 1945-1963.

Google translation:

Heat balance of the earth and global temperature change

Jürgen Lange Heine

Summary: The IPPC's published trend of global temperature anomalies can be explained only superficially by the increase of carbon dioxide in the atmosphere over the last 100 years. Despite steadily rising carbon dioxide levels observed in the years 1945 to 1975, as well as since 1998, a decrease or stagnation in global temperatures occurred that does not fit with the carbon dioxide hypothesis....

Fig. 1 NASA Information on the anomaly of the global annual mean temperatures

.... The observed deviation from a steady rise in temperature from increased solar radiation in the years 1945 to 1975 was due to increased cloud formation by the radioactive condensation nuclei artificially introduced in the years 1945 to 1963 from the nuclear tests in the atmosphere. The stagnation of temperature since 1998 was caused by decreasing solar activity since 1998 ..

From 1900 to 1998, solar radiation increased by 1.3 W / m², but since 1998 it has diminished, and could reach values ​​similar to those of the early 20th century. A drop in global temperature over the next few years is predicted

 Main text

The surface of 511 million square kilometers is covered about 75% of water. The rest are 3% and 22% polar ice land masses, with 8% forest, 8% of arable land and 5% industrial and colonization surface.

Thanks to the enormous amount of water in the oceans of the earth and the high heat capacity of seawater make changes there accumulated thermal energy is the main component of the thermal energy balance of the Earth.

When we talk about climate change, reference is made to the presentation of the so-called. Temperature anomalies, which is published by the ICCP, among others. It is to yearly average values, which are in turn based on a mean value over a defined time interval. (Z. B. 1961-1990). The following Fig.1 the course of the temperature anomalies is shown: 

Fig.1:. NASA Information on the anomaly of the global annual mean temperatures  (after data.giss.nasa.gov/gistemp/station_data/)  See Bil d right 

These are measured temperatures of approximately 35,000 meteorological stations distributed over the earth, with the greater frequency of monitoring stations located in the northern hemisphere.

The oceans play due to their large surface area and their large heat capacity, the key role in climate design earth. They contain 97% of the total water on the planet and are the source of 86% of the evaporating water on the Earth's surface. 78% of global precipitation occurs over the oceans, and only 22% via the land masses.

The response of the Earth's atmosphere on disorders of the heat balance is, in essence, the temperature behavior of the ocean km², with its area of ​​about 400 million, determined its water content of ca.1,3 trillion cubic meters and the interaction with the atmosphere.

The, the atmosphere forming air is a compressible gas at sea level, and has a density of 1.29 kg / m3. Approximately 50% of the air mass of the atmosphere between 5500m altitude and sea level.

The total mass of the atmosphere is ML = 5.14 * 1018kg and the resulting air pressure at sea level is 1013 hPa.

The main components of the Earth's atmosphere are nitrogen N2 78%, 21% oxygen O2, argon Ar to 0.9%, carbon dioxide, CO2 and water vapor to 0.038%, H2 O. While the composition of the air with respect to N2, O2, Ar, and CO2 changes only at high altitude, the water vapor concentration Fig. is strongly dependent on the temperature and the height, s.. 2

Fig. 2: water vapor content as a function of the level

(J. Lange Heine, energy policy in Germany, the business of fear, Athena Media Verlag, ISBN 978-3-86992-054-2) 

If air saturated with water at 20 ° C containing ca.17g water / m³ as water vapor, z. B. transported to an altitude of 5000m, it loses water 16g / m³. This water vapor condenses and falls under certain conditions as precipitation back to earth.

90% of the water content of the atmosphere spread over the first 5500 meters of altitude .Damit weather processes occur mainly in a height range up to about 5500 m from. The integration over the height up to 11000m results in a total amount of water in the atmosphere of about MW = 1.3 ∙ 1016kg and corresponds to a condensed volume of 1.3 ∙ 1013m³. In the oceans, however, is about 1.3 ∙ 1018 m³ about 100,000 times more water than in the atmosphere.

In pure air (without foreign particles) can reach up to 800% relative humidity without condensation occurs. In reality, however, the water vapor condenses at values ​​of a few percent below or above 100%, depending on the nature and concentration of the condensation nuclei in the air. As condensation nuclei for cloud formation serve aerosol particles from the surface components and high-energy ion-forming radiation. Are particularly active radioactive dust and radon decay products, their accumulation in cloud droplets compared to the surrounding air (BI Styra et all. Tellus XVIII (1966, 2) suggesting their involvement in the formation of condensation nuclei.

The distinction between the clouds will clear and more for the height of cloud base into high, medium and low clouds.

High clouds that form in general above 6000m and account for about 13-14% of cloud cover, composed of ice crystals.

Middle clouds that arise at altitudes 2000-5000 m and account for about 20% of cloud cover, made of water drops.

Low clouds are also made of water drops are located at altitudes up to 2000m. They account for about 28-30% of cloud cover.  

High and medium or low clouds can occur simultaneously, but the middle and low clouds are responsible for the precipitation substantially.

Fig.3. Cloud cover and water content of the atmosphere 1983-2010

( www.climate-4you.com / images / Cloud Cover Low Level Observations Since1983 gif)

In Fig.3 the time course of the water content of the atmosphere and of course the clouds from 1983 to 2010 is shown. Fig. 4 shows the variation of annual rainfall from the long-term average. An increase in the mean cloud cover and a drop in the deep clouds in the years from 1998 can be seen from the comparison of the two representations 3 and 4, associated with an increase in the rate of precipitation. The total cloudiness with middle and low clouds, however, remains largely constant at 48%. Despite rainfall, the water content of the atmosphere changes only slightly, but as of 1998 is a sudden drop to 24 mm (see Fig. Discussion below) to see. At the same time, the average cloudiness of 20 increases to 23% and the low clouds decreases from 28 to 25%.

Since this show is stagnating and global warming.

Fig. 4: Deviation in global precipitation over land from the average for the years 1900-2010

(Image credit: NOAA's National Climatic Data Center.)

A comparison of figure 4 with figure 1 shows that stagnation in global temperature anomaly occurs in periods of high rainfall. Both in the periods from 1945 to 1980 as well as from 1998 to 2010 observed a significant positive deviation of rainfall.

Clouds and precipitation are the link of the atmosphere to the ocean.

The amount of water of the oceans, Distributed on its surface gives an average depth of 3800m. But the deeper layers of the ocean hardly contribute to the temperature changes of the surface. At a certain depth, the so-called. Thermoclines the surface temperature of the low temperature equalizes.

Figure 5 shows the increase of the heat content of the ocean from 1970 to 2005 by about 1.6 ∙ 1023 J.

During the same period, the surface temperature increased by 0.4 ° C. Hence the position of the average thermoclines calculated at a depth of about 300m. In this water depth approximately 1/13 of the water masses of the ocean are affected and require for ignition by 1K about 4 ∙ 1023 J.

 

Fig.5 change in the heat content of the oceans

www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/ 

The amount of water contained in the atmosphere corresponds to a condensed volume of 1.3 ∙ 1013 m³. If you distribute the water volume of the atmosphere to the soil surface of 511 ∙ 106 km 2, we obtain a water column of about 25 mm, s. Fig. 3. The heat of vaporization of 2257 kJ / kg of water by the liquid to convert the water is required in the vapor state, there is a whole contained in the water vapor in the Earth latent heat of about 3 ∙ 1022 joules, equivalent to 3 ∙ 104 EJ.

The average evaporation, and precipitation rate is about 1000 mm of water per year. (Baumgartner and Reichel 1975). This means that the cycle Verdampfung- condensation per year, about 40 times runs out.

After this assessment evaporate so every year 520.000Km³ water from the surface. The exact figures are 505,000 cubic kilometers, of which 434,000 cubic kilometers over the oceans and 71,000 km³ across the country. The lack of balance in the amount of about 36,000 km³ is the oceans fed by the rivers again.

With the heat of vaporization of 2257 kJ / kg, this results in a heat quantity of 9.8 ∙ 1023 J / a, which is removed from the oceans annually and a heat quantity of 1.6 ∙ 1023 J / a, which comes from the land, for a total a heat quantity of 11.4 ∙ 1023 J / a or 1.14 ∙ 106 EJ per year. These are offset by the sunlight in a state of equilibrium.

A deviation of annual precipitation rate to 1% (10mm per year) changed this amount of energy for the oceans by about 1 ∙ 1022 J / a. it is possible to change the heat radiation performance of 0,86W / m² oceans calculated.

The berechnetet taking into account the precipitation and temperature development energy balance for the period 1900-1998 now yields the following result:

-Between 1900 and 1945, the ocean energy amount of 1.6 ∙ 1023 J was supplied, resulting from the lower precipitation rate (average 1.2%) of 570 mm, corresponding to approximately 5.7 ∙ 1023 J, a increased due to the increase in temperature of the ocean heat radiation of about 5.6 ∙ 1023 J and until 1945 to ca.0,6 W / m², increased Wärmeinstrahlung (1.6 ∙ 1023 J) composed by increased solar radiation. The increase in heat radiation per year was about 0,013W / m².

-In The period 1945-1980, this additional sunlight rose to 0,93W / m². During this period fell 350mm more rainfall than the statistical means, that on average every year 1% more than normal. This led to a further increase in 1970 as the Wärmeinstrahlung reached the value of the heat loss due to increased rainfall, a drop in temperature. From this point outweighed the effect of rising sun and the temperature rose again.

-In The period 1980 to 1998, again a below-average rainfall of about 1% in each year recorded, during the same period the solar radiation rose to 1.3 W / m², which led to an increase in temperature in 1998 to 0.55 K.

-From 1998 to 2010 uses a stronger 1.5% chance of precipitation. A stagnation temperature continues to increase from 1998 was the result.

The energy balances of each of the periods lead to the conclusion that the effective solar radiation must be increased by about 1.3 W / m² 1900-1998. This result is also confirmed by the following considerations Albedoveränderungen and cloud formation processes.

Scattering and reflection of the striking of the sun to the earth's surface radiation leads to an average albedo of 30%. Albedo is the amount of backscattering and reflection of solar radiation by atmospheric clouds and the earth's surface, it is the heat balance of the earth does not benefit.

Stronger cloudiness leads to higher albedo values, low to lower values, the latter connected to the then higher radiation on the earth's surface.

The following figures 6 and 7 show the measurements of the Erdalbedos the years 1985 to 2010, compared to the global cloud cover 1983-2010

Fig.6 change the Erdalbedo by (Palle, E, et all 2004) http://www.iac.es/galeria/epalle/reprints/Palle_etal_Science_2004.pdf

 Fig.7 Global Cloud cover from 1983

( www.climate-4you.com / images / Cloud Cover Low Level Observations Since1983 gif)

Approximately 5% change in total cloud cover have according to these results, a change in the Erdalbedo about 6% of 30 to 28.2% result. This means that each percent of change of cloud cover causes an albedo of 1.2%. The solar radiation so that changes by about +/- 1.4 W / m² from 239.4 to 240.8 W / m² and 238 W / m² with a change in cloud cover by +/- 1%.

According to the theory of Svensmark enhanced cosmic ray ion formation is responsible for the creation of additional low clouds.

Fig. 8: Cosmic radiation and cloud cover by Svensmark

Marsh & Svensmark 2003 ( DOI: 10.1029 / 2001JD001264.)

20% variation with respect. Cosmic rays mean then 2% variation in cloud cover.

Cosmic radiation is a high energy particle radiation that comes from the sun, the Milky Way and distant galaxies.

The intensity of cosmic radiation reaching the Earth's atmosphere is a function of the solar activity caused by the fault or shielding the Earth's magnetic field.

The geomagnetic index, the so-called. Aa index, is a measure of this error, and therefore a measure of the shielding effect of the earth's field to cosmic radiation. The aa index is specified in nT. Its history since 1860 is shown in the following figure 9, from which it can be seen that the geomagnetic index from a low point, which was about 1900 until about 2000 has steadily increased.

 Fig.9: The geomagnetic index

[ http://www.ngdc.noaa.gov/stp/geomag/aastar.html ]

Between cosmic rays and CR aa index by Palle the derivable from the following Fig.10 context: 

CR = 5000 45 .

Figure 10. The influence of cosmic rays on terrestrial low clouds and global warming </ address>

in the years 1984-1993 </ address>

E. Palle Bago and CJ Butler: Astronomy & Geophysics, August 2000. Vol 41, Issue 4, pp.18-22.

1900, the aa-index was 14nT and climbed up to the year 1990 to ca.30nT.

Thus the cosmic radiation has decreased from a value of 4370 in 1900 to 3650 in 1990, and the cloud cover with low clouds decreased when using the results of Svensmark by 2%.

As low clouds Cloud cover accounts for about 50% of the total cloud cover, it can be assumed by a drop in total cloud cover and 1990 by about 1%, which means an additional solar irradiation of ca.1,4 W / m² to 1990.

The increase from 1900 to 1998 solar activity is the sole cause of the increase in global temperature, which was only interrupted by periods of high rainfall in the years 1945-1970.

Since the year 1998, the sunspot activity drops significantly and reached by Cycle 24 values ​​similar to those in 1900. The cosmic radiation increases and leads to increased rainfall.

In the coming years is expected to aa index of about 15nT, with a corresponding increase in cosmic radiation, increased cloud formation and sinking global temperature.

The increased rainfall in the period 1945 to 1970 is due to an additional source of ionizing radiation, whose origins are to be found in the nuclear tests of the time period 1945-1963. Air pollution eliminated as the cause for this period.

Huge quantities of radioactive dust and finely divided matter were thrown by the explosions into the stratosphere, distributed with the air currents around the world and were a constant source of ionizing micro dust for the formation of condensation nuclei in the troposphere.

Between 1951 and 1963, z. B. the strontium content increased in the stratosphere constantly with corresponding effects on weather patterns and took off in 1963 after the nuclear test stop slowly to 1974 again.

It was not until 1974 that source is nuclear radiation dries up and comes out of the question for cloud formation.

Between 1945 and 1974, the cloud formation is thus influenced by additional radioactive radiation that comes from the nuclear tests, an indirect proof for the theory of Svensmark. Only from that time, the influence of cosmic rays falling down again by the climate factor and the temperature increase is in accordance with the increase in solar radiation on.

From 1998, the aa index decreases and reaches 2010 levels by 15 that existed in the early 19th century. The cosmic rays, and thus the cloud cover increase since that time. The solar radiation additional drops to values ​​that prevailed at the beginning of the 20th century. This leads to a decline in global temperature. When this development comes to a standstill depends solely on the history of solar activity.

(A more detailed description can be used as pdf - load file) 

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New paper shows negative feedback from clouds 'may damp global warming'

A paper published today in The Journal of Climate uses a combination of two modelling techniques to find that negative feedback from clouds could result in "a 2.3-4.5% increase in [model projected] cloudiness" over the next century, and that "subtropical stratocumulus [clouds] may damp global warming in a way not captured by the [Global Climate Models] studied." This strong negative feedback from clouds could alone negate the 3C alleged anthropogenic warming projected by the IPCC.

As Dr. Roy Spencer points out in his book, 

"The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling."

According to the authors of this new paper, current global climate models "predict a robust increase of 0.5-1 K in EIS over the next century, resulting in a 2.3-4.5% increase in [mixed layer model] cloudiness." 

EIS or estimated inversion strength has been shown by observations to be correlated with cloudiness, as demonstrated by the 2nd graph below from the University of Washington, indicating a 1 K increase in EIS results in an approximate 4-5% increase in low cloud cover [CF or cloud fraction]. Thus, a combination of observational data and modelling indicate clouds have a strong net negative feedback upon global warming that is "not captured" by current climate models. 

Related posts

Journal of Climate 2012 ; e-View

doi: http://dx.doi.org/10.1175/JCLI-D-12-00188.1

CMIP3 Subtropical Stratocumulus Cloud Feedback Interpreted Through a Mixed-Layer Model

PETER M. CALDWELL,* YUNYAN ZHANG, and STEPHEN A. KLEIN

Lawrence Livermore National Lab, Livermore CA

Abstract

Large-scale conditions over subtropical marine stratocumulus areas are extracted from global climate models (GCMs) participating in Phase 3 of the Coupled Model Intercomparison Project (CMIP3) and used to drive an atmospheric mixed layer model (MLM) for current and future climate scenarios. Cloud fraction is computed as the fraction of days where GCM forcings produce a cloudy equilibrium MLM state. This model is a good predictor of cloud fraction and its temporal variations on timescales longer than 1 week but overpredicts liquid water path and entrainment.

GCM cloud fraction compares poorly with observations of mean state, variability, and correlation with estimated inversion strength (EIS). MLM cloud fraction driven by these same GCMs, however, agrees well with observations, suggesting that poor GCM low cloud fraction is due to deficiencies in cloud parameterizations rather than large-scale conditions. However, replacing the various GCM cloud parameterizations with a single physics package (the MLM) does not reduce inter-model spread in low-cloud feedback because the MLM is more sensitive than the GCMs to existent inter-model variations in large-scale forcing. This suggests that improving GCM low cloud physics will not by itself reduce inter-model spread in predicted stratocumulus cloud feedback.

Differences in EIS and EIS change between GCMs are found to be a good predictor of current-climate MLM cloud amount and future cloud change. CMIP3 GCMs predict a robust increase of 0.5-1 K in EIS over the next century, resulting in a 2.3-4.5% increase in MLM cloudiness. If EIS increases are real, subtropical stratocumulus may damp global warming in a way not captured by the GCMs studied.

From the University of Washington Dept. of Atmospheric Sciences:

A new scaling for low cloud cover

Contact | Publications | Research | UW Atmospheric Sciences | UW

Observations show that on daily to interannual timescales, stratiform low cloud fraction CF is strongly correlated with the lower tropospheric stability LTS, defined as the difference between the potential temperature q of the free troposphere (700 hPa) and the surface, LTS = q₇₀₀-q₀ (Klein and Hartmann 1993).

Relationships between LTS and CF from observations in the tropics (Slingo 1980) and subtropics (Klein and Hartmann 1993) have been used in the parameterization of low cloud cover in general circulation models (e.g. Slingo 1987; Rasch and Kristjansson 1998) used to predict climate changes. They are also a key assumption in the thermostat hypothesis of Miller (1997) and in the climate sensitivity study of Larson et al. (1999). Both of these studies result in a strong negative low cloud feedback on climate changes due to a marked increase in low cloud cover as the sea surface temperature SST increases. However, it has yet to be demonstrated whether the observationally-derived LTS-CF relationships will hold in a changed climate.

We have derived a new formulation, called the estimated inversion strength (EIS) to estimate the strength of the PBL inversion given the temperatures at 700 hPa and at the surface (Wood and Bretherton 2006). The EIS, which like LTS depends only upon the 700 hPa and surface temperatures, accounts for the general observation that the free-tropospheric temperature profile is often close to a moist adiabat and its lapse rate is strongly temperature dependent. Therefore, for a given LTS, the EIS is greater at colder temperatures. We demonstrate that while the seasonal cycles of LTS and low cloud cover CF are strongly correlated in many regions, no single relationship between LTS and CF can be found that encompasses the wide range of temperatures occurring in the tropics, subtropics, and midltatitudes. However, a single linear relationship between CF and EIS explains 83% of the regional/seasonal variance in stratus cloud amount (see Figure below), suggesting that EIS is a more regime-independent predictor of stratus cloud amount than is LTS under a wide range of climatological conditions.

The result has some potentially important implications for how low clouds might behave in a changed climate. In contrast to Miller's (1997) thermostat hypothesis that a reduction in the lapse rate (Clausius-Clapeyron) will lead to increased LTS and increased tropical low cloud cover in a warmer climate, our result suggests that low clouds may be much less sensitive to changes in the temperature profile if the vertical profile of tropospheric warming follows a moist adiabat. There is some evidence that recent syntheses of state-of-the-art climate models are demonstrating a weaker cloud feedback than previously thought (Soden et al. 2006). Our results give some physical basis for why this might be expected. They also provide strong constraints for evaluating these models.

LEFT: Low cloud cover CF, vs LTS (top) and vs EIS (bottom). Solid circles show long term seasonal means from the tropics and subtropics, while open circles are for the colder midlatitude regions. Notice that EIS is a much more appropriate measure across a broader range of temperatures, which suggests it may have skill in predicting how low clouds may change in a future climate. 

References:

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Miller, R. L.: 1997, Tropical thermostats and low cloud cover. J. Clim., 10, 409-440.

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Soden, B. J. and I. M. Held, 2006: An assessment of climate feedbacks in coupled ocean-atmosphere models. J. Clim., 19, 3354-3360.

Wood, R. and D. L. Hartmann: 2006, Spatial variability of liquid water path in marine boundary layer clouds: The importance of mesoscale cellular convection. J. Clim., 19, 1748-1764.

Wood, R. and C. S. Bretherton, 2006: On the relationship between stratiform low cloud cover and lower tropospheric stability. J. Clim., in press.