Showing posts sorted by relevance for query dr roy spencer clouds. Sort by date Show all posts
Showing posts sorted by relevance for query dr roy spencer clouds. Sort by date Show all posts

Monday, November 18, 2013

NCAR scientist admits IPCC may be wrong on clouds, may have a net cooling effect instead of warming

Cloud expert Dr. Greg Holland, senior scientist at the National Center for Atmospheric Research, says in a Huff Post article today, "The current consensus on this from the IPCC is that the clouds are in the net warming. Not real sure. There is a possibility that the other effects are dominating and they could be cooling. So this is one of those areas that we need to know a lot more." 

 Indeed, many peer-reviewed studies find clouds have a net cooling negative-feedback effect, opposite of the claims of the IPCC of a net warming positive-feedback effect. This single erroneous programming assumption of the IPCC climate models, along with an inability to model cloud cover, can alone explain all warming of the 20th century without any influence of greenhouse gases.   

As Dr. Roy Spencer notes,

"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."


Clouds Float Front & Center In Climate Change Narrative (VIDEO)

Posted: 11/18/2013

Most of us learned all about clouds in grade school -- from the different types of clouds there are in the sky to how they form. But for climate scientists, there is much more to learn about clouds -- especially when it comes to the role clouds play in climate change.

Clouds can trap heat in Earth's atmosphere, causing warmer temperatures on the planet's surface. But they also reflect solar radiation, resulting in lower temperatures. This dual role has made it tricky to build reliable models of our changing climate -- and even led some scientists, who are far outside the mainstream, to push back against the large body of evidence showing that climate change is a real problem.

So, what exactly is the overall influence of clouds on climate change and our planet's future? To cut through the fog, I spoke with Dr. Greg Holland, senior scientist at the National Center for Atmospheric Research, for answers.

 

Watch the video above, and/or click the link below for a transcript. Don't forget to sound off in the comments section at the bottom of the page. Talk nerdy to me!

JACQUELINE HOWARD: Hey everyone. Jacqueline Howard here. All around the world, sophisticated supercomputers are crunching huge amounts of data to create climate models, or simulations, that help us understand how our world is changing. Now, this data includes global temperatures, extreme weather events, rainfall, sea levels, and even wind patterns. Sounds crazy cool, right? But there remains some doubt around one critical component: Clouds. And because of this, some people question the very validity of climate models. As a 2012 article in The New York Times puts it, “clouds’ effect on climate change is last bastion for dissenters.” So, what does that mean? What do mainstream scientists say about clouds and the role they play in climate change? Can we harness clouds to save the planet? For answers, I reached out to the prominent climate expert Dr. Greg Holland. He’s a senior scientist at the National Center for Atmospheric Research in Boulder, Colorado.

DR. GREG HOLLAND: The really important thing about clouds is understanding this very fine interaction between the warming part, and the cooling part, and how that may actually impact future climate. Right now, the scientific consensus is that the warming, in other words the net effect of redistribution of water vapor and the re-radiation of heat back down to the surface, dominates. And unfortunately that’s bad news because if that is true, that accelerates global change rather than helping us mitigate it.

JH: Did you get that? Clouds both heat and cool our planet. That's why some say it’s difficult to predict cloud behavior and the net effect they have on our global climate. But a recent report from the Intergovernmental Panel on Climate Change, or IPCC, hints at a more certain relationship between clouds and our climate.

GH: The current consensus on this from the IPCC is that the clouds are in the net warming. Not real sure. There is a possibility that the other effects are dominating and they could be cooling. So this is one of those areas that we need to know a lot more.

JH: The cooling component is what fuels some of the criticism current climate models receive. See, low-level thick clouds, like stratus clouds, keep us cool by reflecting solar radiation, or they may absorb heat emitted from our planet’s surface and then radiate that heat out into space. But high, thin clouds, like cirrus clouds, primarily keep us warm by absorbing heat emitted from our planet’s surface and then re-radiating that heat back down to us. Another way clouds may warm our planet is by distributing water vapor.

GH: That last one is a critical one because water vapor is the biggest greenhouse gas we have. It’s about 70 to 80 percent of all of the greenhouse warming on the Earth is due to water vapor. [Why the remaining alleged 20% of the greenhouse warming from CO2 indicates that climate sensitivity is only 0.33C to a doubling of CO2 levels]

JH: What if we actually controlled cloud behavior to mitigate global climate change ourselves? Think about it. If low-level clouds cool the planet, what if we artificially whip some up to keep human-induced warming in check?

GH: There are actually very good scientific studies that have looked at this using complex computer models and some fairly advanced theory. If we can increase the size of that bank of cloud, then we can cool the locality, but also, we can increase it enough, and the models have shown this and the theories have shown this, we could increase it enough to be able to have a net cooling effect on the world at large. So there’s one possibility where we could, what is called geoengineering, the climate to use clouds to our advantage.

JH: Clouds for the win! But geoengineering can be risky business. For instance, one proposal is to amp up production of these cooling clouds by what's called cloud brightening. Now, that's when you blast salty mist into the air to speed up formation of water droplets in clouds. But do you think we should be looking up at clouds to combat human-induced climate change here on Earth? Let me know in the comments. Leave your thoughts in the cloud. Talk nerdy to me!

 Related:

New paper finds climate models grossly underestimate cooling from clouds

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Friday, July 29, 2011

Climate change far less serious than 'alarmists' predict says NASA scientist


By TAMARA COHEN    Daily Mail Online

Last updated at 2:03 AM on 30th July 2011

Dr Roy Spencer: He claims climate change is less serious than forecasts suggest
Dr Roy Spencer: He claims climate change is less serious than forecasts suggest

Climate change is far less serious than ‘alarmists’ predict, an eminent NASA scientist has said.

Dr Roy Spencer, who works on the space agency’s temperature-monitoring satellites, claimed they showed ‘a huge discrepancy’ between the real levels of heating and forecasts by the United Nations and other groups.

After looking at the levels of radiation in the atmosphere over the past ten years, he believes the Earth releases a lot more heat into space than previously thought.

This means carbon dioxide emissions do not trap as much heat or force temperatures up as much as global warming bodies fear.

Dr Spencer, a climatologist at the University of Alabama, said his satellite readings between 2000 and 2011 show far smaller temperature rises than six climate models which are used by international governments and corporations to predict changes to our climate in the future.

He said: ‘The satellite observations suggest there is much more energy lost to space during and after warming than the climate models show. 

'There is a huge discrepancy between the data and the forecasts that is especially big over the oceans.’

However critics say his research is over too short a period to draw conclusions and ignores other factors. 

Dr Spencer is the first scientist to examine the data from Nasa satellites in relation to climate change. 
 

More...

He has long believed the build-up of hot air produces more clouds, which have a cooling effect on the Earth, counteracting global warming to some extent. 

However his study, published in the journal Remote Sensing, does conclude that the limited heating he has found remains an ‘unsolved problem’.

Bob Ward of the Grantham Research Institute on Climate Change and the Environment at the London School of Economics, said: ‘It’s a simplistic theory and we will need to look very closely at these measurements as he is far from proving conclusively that this is the cause.

‘He has taken these measurements over a very short time during which the Earth has not heated as much as it did in the late 1990s, and scientists expect this heating to resume.

‘Satellites also drift over time, getting further and closer to the Earth, which can affect the readings.’
Sceptical: Greenpeace fiercely oppose nuclear power and have campaigned on the perils of global warming for decadesr
Sceptical: Greenpeace fiercely oppose nuclear power and have campaigned on the perils of global warming for decades

Climate change sceptics are also cautious about his conclusions. Dr David Whitehouse, of the Global Warming Policy Foundation said:  ‘It correctly states that the computer models of climate have many flaws and have been unable to explain how the earth has warmed up in recent decades. 

‘It’s a very interesting paper though only time will tell if its analysis - that the earth radiates more heat out into space than we thought - stands up.’

The United Nations climate change body, the Intergovernmental Panel on Climate Change, has been dogged by controversy over its impartiality. 

Set up to provide science-based advice to politicians, last month it was criticized for using a Greenpeace campaigner to help write an ‘impartial’ report on green energy.

The study claimed that the world could meet nearly 80 per cent of its energy by 2050 from renewable sources such as wind farms and solar panels.

Greenpeace fiercely opposes nuclear power and has campaigned on the perils of global warming for decades. 

Last year, the IPCC was at the centre of a major row when it was forced to admit that it had exaggerated the threat of global warming to glaciers.
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Friday, May 9, 2014

New paper finds clouds have a net negative-feedback cooling effect

A paper published today in Climate Dynamics finds that clouds have a large net negative feedback cooling effect on the Earth and atmosphere. However, all current IPCC models adopt net positive feedbacks for water vapor and clouds, and this false assumption may account for a large portion of the exaggerated warming models project:


According to the authors, "A large degree of uncertainty in global climate models (GCMs) can be attributed to the representation of clouds and how they interact with incoming solar and outgoing longwave radiation." The paper finds "The averaged SW [shortwave from the Sun], LW [longwave IR from the Earth], and net CRFs [total cloud fractions] from CERES EBAF are −50.1, 27.6, and −22.5 Wm−2, respectively, indicating a net cooling effect of clouds on the TOA [top of the atmosphere] radiation budget."

By way of comparison, the net cooling effect from clouds of -22.5 W/m2 at the top of the atmosphere is about 6 times greater than the assumed radiative forcing from a doubling of CO2 levels of 3.7 W/m2.

As Dr. Roy Spencer notes,
"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."
Indeed, the authors of this paper find that " CF [total cloud fraction] is a primary modulator of warming (or cooling) in the atmosphere" and that the net effect of more clouds produces a net negative-feedback cooling effect. 

Evaluation of CMIP5 simulated clouds and TOA radiation budgets using NASA satellite observations

Erica K. Dolinar et al 

A large degree of uncertainty in global climate models (GCMs) can be attributed to the representation of clouds and how they interact with incoming solar and outgoing longwave radiation. In this study, the simulated total cloud fraction (CF), cloud water path (CWP), top of the atmosphere (TOA) radiation budgets and cloud radiative forcings (CRFs) from 28 CMIP5 AMIP models are evaluated and compared with multiple satellite observations from CERES, MODIS, ISCCP, CloudSat, and CALIPSO. The multimodel ensemble mean CF (57.6 %) is, on average, underestimated by nearly 8 % (between 65°N/S) when compared to CERES–MODIS (CM) and ISCCP results while an even larger negative bias (17.1 %) exists compared to the CloudSat/CALIPSO results. CWP bias is similar in comparison to the CF results, with a negative bias of 16.1 gm−2 compared to CM. The model simulated and CERES EBAF observed TOA reflected SW and OLR fluxes on average differ by 1.8 and −0.9 Wm−2, respectively. The averaged SW [shortwave], LW [longwave], and net CRFs [total cloud fractions] from CERES EBAF are −50.1, 27.6, and −22.5 Wm−2, respectively, indicating a net cooling effect of clouds on the TOA [top of the atmosphere] radiation budget. The differences in SW and LW CRFs between observations and the multimodel ensemble means are only −1.3 and −1.6 Wm−2, respectively, resulting in a larger net cooling effect of 2.9 Wm−2 in the model simulations. A further investigation of cloud properties and CRFs reveals that the GCM biases in atmospheric upwelling (15°S–15°N) regimes are much less than in their downwelling (15°–45°N/S) counterparts over the oceans. Sensitivity studies have shown that the magnitude of SW cloud radiative cooling increases significantly with increasing CF at similar rates (~−1.25 Wm−2 %−1) in both regimes. The LW cloud radiative warming increases with increasing CF but is regime dependent, suggested by the different slopes over the upwelling and downwelling regimes (0.81 and 0.22 Wm−2 %−1, respectively). Through a comprehensive error analysis, we found that CF [total cloud fraction] is a primary modulator of warming (or cooling) in the atmosphere. The comparisons and statistical results from this study may provide helpful insight for improving GCM simulations of clouds and TOA radiation budgets in future versions of CMIP.

Related:


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Friday, April 22, 2011

Unsettled Science: Effects of clouds on climate still unknown

A press release today illustrates how climate science continues to struggle to understand the net effect of clouds upon global climate. IPCC climate models assume a slight net warming effect from clouds [personal communication with an atmospheric scientist/cloud specialist at JPL], yet the press release today states, "most clouds have a net cooling effect." Furthermore, the poorly-understood natural fluctuations in cloud cover could alone account for global warming or global cooling, as illustrated by Dr. Roy Spencer in his new 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."
Until cloud effects are much better understood (as well as a host of other factors such as ocean oscillations), computer climate models will remain computer fantasy games.

Effect of Cloud-Scattered Sunlight on Earth's Energy Balance Depends on Wavelength of Light


Press Release 4/22/2011 2:25 PM EDT  Source: Pacific Northwest National Laboratory

Accounting for wavelength effects will likely improve climate models

RICHLAND, Wash. -- Atmospheric scientists trying to pin down how clouds curb the amount of sunlight available to warm the earth have found that it depends on the wavelength of sunlight being measured. This unexpected result will help researchers improve how they portray clouds in climate models.

Additionally, the researchers found that sunlight scattered by clouds — the reason why beachgoers can get sunburned on overcast days — is an important component of cloud contributions to the earth's energy balance. Capturing such contributions will increase the accuracy of climate models, the team from the Department of Energy's Pacific Northwest National Laboratory reported in Geophysical Research Letters earlier this month.

"The amount of the sun's energy that reaches the earth's surface is the main driver of the earth's temperature. Clouds are one of the least understood aspects of climate change. They can block the sun, but light can also bounce off one cloud into another cloud's shadow and increase the solar energy hitting earth," said PNNL atmospheric scientist Evgueni Kassianov.

Clouds both cool down and warm up the earth's surface. They cool the earth by reflecting some sunlight up into outer space, and they warm it by bouncing some sunlight down to the surface. Overall, most clouds have a net cooling effect, but atmospheric scientists need to accurately measure when they cool and warm to produce better climate models that incorporate clouds faithfully.

But it's a hard number to get. Fair-weather clouds are big puffy white objects that bounce a lot of light around. They can make the sky around them look brighter when they're there, but they float about and reform constantly. Cloud droplets and aerosol particles in the sky — tiny bits of dirt and water in the air that cause haziness — scatter light in three dimensions, even into cloud shadows.

To determine the net cloud effect, researchers need two numbers. First they need to measure the total amount of sunlight in a cloudy sky. Then they need to determine how bright that sky would be without the clouds, imagining that same sky to be blue and cloudless, when aerosols are in charge of a sky's brightness. The difference between those numbers is the net cloud effect.

Researchers have traditionally estimated the net cloud effect by measuring a broad spectrum of sunlight that makes it to the earth's surface, from ultraviolet to infrared. But clouds are white — that's because the large water droplets within them scatter light of all colors almost equally in the visible spectrum, the part of the electromagnetic spectrum that includes the colors of the rainbow.

On the other hand, aerosols — both within clouds and in the open sky — bounce different-colored light unequally. Broadband measurements that fail to distinguish color differences might be covering up important details, the researchers thought.

Instead of taking one broadband measurement that covers everything from ultraviolet to infrared, Kassianov and crew wanted to determine how individual wavelengths contribute to the net cloud effect. To do so, the team used an instrument that can measure brightness at four different wavelengths of color — violet, green, orange, red — and two of infrared.

In addition, this instrument, a spectral radiometer at DOE's Atmospheric Radiation Measurement Climate Research Facility located on the southern Great Plains in Oklahoma, allowed the team to calculate what the brightness would be if the day sported a cloudless, blue sky. The spectral measurements taken by the radiometer can be converted into the amount and properties of aerosols. Then aerosol properties can be used to calculate clear blue sky brightness.

Clouds Gone Wild

Comparing measured values for cloudy sky to the calculated values for clear sky, the researchers found that, on average, puffy fair-weather clouds cool down the earth's surface by several percent on a summer day. Although clouds cool overall, two components that the researchers looked at — from direct and scattered sunlight — had opposite effects.

The direct component accounts for the shade provided by clouds and cools the earth. The second component accounts for the sunlight scattered between and under clouds, which makes the sky brighter, warming the earth.

"The sunlight scattered by clouds can heat the surface," said Kassianov. "We all know that we can still get sunburned on cloudy days. This explains why."

In the Oklahoma summer, the scattered-light effect measured by the researchers could be quite large. For example, if a cloud passed over the instrument, the measured cloudy sky brightness exceeded calculated clear sky value by up to 30 percent. Kassianov attributes that large difference to scattered sunlight being "caught on tape" by the radiometer.

"Sunlight scattered by three-dimensional, irregular clouds is responsible for the observed large difference. The one-dimensional cloud simulations currently used in large-scale climate models don't capture this diffuse light," said Kassianov.

Aerosols' Day in the Sky

The team also found that the effect changed depending on the measured visible-spectrum wavelength, and whether the light was direct or scattered.

With direct light, the cooling caused by clouds was weakest on the violet end of the spectrum and strongest at infrared. With scattered light, warming caused by clouds was also weakest at violet and the strongest at infrared. Overall, the least cooling and warming occurred at violet, and the most cooling and warming occurred at infrared.

Because large droplets in clouds scatter sunlight almost uniformly across the spectrum, the clouds themselves can't be the reason why different wavelengths contribute differently to the net cloud effect. Compared to cloud droplets, aerosols are more than 100 times smaller and scatter wavelengths differently. These results suggest that aerosols — which not only cause haziness but contribute to cloud formation as well — are responsible for the wavelength differences, something researchers need to be aware of as they study clouds in the sky.

"If you want to study how aerosols and clouds interact," said Kassianov, "you need to look in the region of the spectrum where aerosol effects are significant. If you want to fish, you go where the fish are biting."

Reference: Kassianov E., Barnard J., Berg L.K., Long C.N., and C. Flynn, Shortwave Spectral Radiative Forcing of Cumulus Clouds from Surface Observations, Geophys Res Lett, April 2, 2011, DOI 10.1029/2010GL046282 (http://www.agu.org/pubs/crossref/2011/2010GL046282.shtml).
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Tuesday, August 7, 2012

New paper finds climate models grossly underestimate cooling from clouds

A recent paper published in the Journal of Climate finds that climate models grossly underestimate cooling of the Earth's surface due to clouds. According to the authors, "Coupled model intercomparison project (CMIP3) simulations of the climate of the 20th century show 40±20 W m−2 too little net cloud radiative cooling at the surface. Simulated clouds have correct radiative forcing when present, but models have ~50% too few clouds." 

 By way of comparison, the 40 W m-2 underestimate of cooling from clouds is more than 10 times the alleged warming from a doubling of CO2 concentrations [3.7 W m-2]. 

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."
This paper and a host of others demonstrate that many of the key assumptions in climate models  have been falsified by observations, therefore, the model predictions are also false.

Journal of Climate 2012 ; e-View
doi: http://dx.doi.org/10.1175/JCLI-D-11-00618.1

Observations of stratocumulus clouds and their effect on the eastern Pacific surface heat budget along 20°S

Simon P. de Szoeke, Sandra Yuter, David Mechem, Chris W. Fairall, Casey Burleyson, and Paquita Zuidema

Abstract
Widespread stratocumulus clouds were observed on 9 transects from 7 research cruises to the southeastern tropical Pacific Ocean along 20°S, 75°-85°W in October-November 2001-2008. The nine transects sample a unique combination of synoptic and interannual variability affecting the clouds; their ensemble diagnoses longitude-vertical sections of the atmosphere, diurnal cycles of cloud properties and drizzle statistics, and the effect of stratocumulus clouds on surface radiation. Mean cloud fraction was 0.88 and 67% of 10-minute overhead cloud fraction observations were overcast. Clouds cleared in the afternoon (15 h local) to a minimum of fraction of 0.7. Precipitation radar found strong drizzle with reflectivity above 40 dBZ.
Cloud base heights rise with longitude from 1.0 km at 75°W to 1.2 km at 85°W in the mean, but the slope varies from cruise to cruise. Cloud base-lifting condensation level (CB-LCL) displacement, a measure of decoupling, increases westward. At night CB-LCL is 0-200 m, and increases 400 m from dawn to 16 h local time, before collapsing in the evening.
Despite zonal gradients in boundary layer and cloud vertical structure, surface radiation and cloud radiative forcing are relatively uniform in longitude. When present, clouds reduce solar radiation by 160 W m−2 and radiate 70 W m−2 more downward longwave radiation than clear skies. Coupled model intercomparison project (CMIP3) simulations of the climate of the 20th century show 40±20 W m−2 too little net cloud radiative cooling at the surface. Simulated clouds have correct radiative forcing when present, but models have ~50% too few clouds.
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Friday, July 29, 2011

Earth's Atmosphere May Be More Efficient at Releasing Energy to Space Than Climate Models Indicate, Satellite Data Suggest

ScienceDaily (July 29, 2011) Data from NASA's Terra satellite suggests that when the climate warms, Earth's atmosphere is apparently more efficient at releasing energy to space than models used to forecast climate change may indicate.

The result is climate forecasts that are warming substantially faster than the atmosphere, says Dr. Roy Spencer, a principal research scientist in the Earth System Science Center at The University of Alabama in Huntsville.

The previously unexplained differences between model-based forecasts of rapid global warming and meteorological data showing a slower rate of warming have been the source of often contentious debate and controversy for more than two decades.

In research published this week in the journal Remote Sensing, Spencer and UA Huntsville's Dr. Danny Braswell compared what a half dozen climate models say the atmosphere should do to satellite data showing what the atmosphere actually did during the 18 months before and after warming events between 2000 and 2011.

"The satellite observations suggest there is much more energy lost to space during and after warming than the climate models show," Spencer said. "There is a huge discrepancy between the data and the forecasts that is especially big over the oceans."

Not only does the atmosphere release more energy than previously thought, it starts releasing it earlier in a warming cycle. The models forecast that the climate should continue to absorb solar energy until a warming event peaks.
Instead, the satellite data shows the climate system starting to shed energy more than three months before the typical warming event reaches its peak.

"At the peak, satellites show energy being lost while climate models show energy still being gained," Spencer said.
This is the first time scientists have looked at radiative balances during the months before and after these transient temperature peaks.

Applied to long-term climate change, the research might indicate that the climate is less sensitive to warming due to increased carbon dioxide concentrations in the atmosphere than climate modelers have theorized. A major underpinning of global warming theory is that the slight warming caused by enhanced greenhouse gases should change cloud cover in ways that cause additional warming, which would be a positive feedback cycle.

Instead, the natural ebb and flow of clouds, solar radiation, heat rising from the oceans and a myriad of other factors added to the different time lags in which they impact the atmosphere might make it impossible to isolate or accurately identify which piece of Earth's changing climate is feedback from human-made greenhouse gases.
"There are simply too many variables to reliably gauge the right number for that," Spencer said. "The main finding from this research is that there is no solution to the problem of measuring atmospheric feedback, due mostly to our inability to distinguish between radiative forcing and radiative feedback in our observations."

For this experiment, the UA Huntsville team used surface temperature data gathered by the Hadley Climate Research Unit in Great Britain. The radiant energy data was collected by the Clouds and Earth's Radiant Energy System (CERES) instruments aboard NASA's Terra satellite.

The six climate models were chosen from those used by the U.N.'s Intergovernmental Panel on Climate Change. The UA Huntsville team used the three models programmed using the greatest sensitivity to radiative forcing and the three that programmed in the least sensitivity.


Journal Reference:
  1. Roy W. Spencer, William D. Braswell. On the Misdiagnosis of Surface Temperature Feedbacks from Variations in Earth’s Radiant Energy Balance. Remote Sensing, 2011; 3 (8): 1603 DOI: 10.3390/rs3081603
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Sunday, August 3, 2014

New paper finds marine clouds cause a negative-feedback cooling effect on climate

A new paper published in Nature Geoscience finds global marine clouds exert a negative feedback cooling effect on Earth's surface temperatures. However, all current IPCC models adopt net positive feedbacks for water vapor and clouds, and this false assumption may account for a large portion of the exaggerated warming models project (in addition to the climate being less sensitive to CO2 than the IPCC assumes).

 According to the authors, 
"a 6% increase in the albedo of global marine stratiform clouds could offset the warming that would result from a doubling of atmospheric CO2 concentrations" i.e. just clouds over the oceans alone, not considering clouds over land.
and as previously noted by Dr. Roy Spencer,
"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 paper,  
"The estimated intrinsic [marine cloud] forcing is −0.49 ± 0.33 Wm−2, and for the extrinsic (cloud-cover effect) forcing, we estimate −0.46 ± 0.31 Wm−2" "We have also estimated the long-wave component of aerosol–cloud radiative forcing (Supplementary Information); the estimated long-wave TOA [Top Of Atmosphere] intrinsic and extrinsic forcings are −0.01 and 0.09 W m−2, respectively."
Adding the 4 forcings obtains a net shortwave and longwave marine cloud forcing of negative 0.87 Wm-2, higher than many climate sensitivity estimates for a doubling of CO2 levels. 


Global mean intrinsic aerosol-cloud radiative forcing by global marine clouds is estimated to be negative 0.49 Wm-2
Excerpt:

 Using equations (1) and (2), we estimate the aerosol–cloud
 radiative   forcing   for   global   single-layer   marine   warm   clouds
 between   60◦ S   and   60◦ N.   The   estimated   intrinsic   forcing   is
 −0.49 ± 0.33 W m−2,   and   for   the   extrinsic   (cloud-cover effect)
 forcing, we estimate −0.46 ± 0.31 W m−2, a similar magnitude
 to the estimated intrinsic forcing (Supplementary Fig. 2). This
 corroborates the finding in ref. 21 that the combined Twomey
 and   LWP   effects   (that   is,   intrinsic   forcing)   are   comparable   in
 magnitude to the cloud-cover effect. It should be noted that the
 observed positive correlation between  cloud  cover and aerosol
 level may be subject to other processes or artefacts 22,23, including
 cloud contamination of satellite-retrieved AOD, co-variation of
 cloud fraction and relative humidity/wind speed, cloud processing
 of aerosols, and so on. Owing to uncertainties that cannot be
 quantified directly, the magnitude of the extrinsic forcing may
 be biased. We have also estimated the long-wave component of
 aerosol–cloud radiative forcing (Supplementary Information); the
 estimated long-wave Top Of Atmosphere intrinsic and extrinsic 
forcings are −0.01  and 0.09 W m−2, respectively.




Satellite-based estimate of global aerosol–cloud radiative forcing by marine warm clouds


Nature Geoscience
 
 
doi:10.1038/ngeo2214
Received
 
Accepted
 
Published online
 
Changes in aerosol concentrations affect cloud albedo and Earth’s radiative balance1. Aerosol radiative forcing from pre-industrial time to the present due to the effect of atmospheric aerosol levels on the micro- and macrophysics of clouds bears the largest uncertainty among external influences on climate change1. Of all cloud forms, low-level marine clouds exert the largest impact on the planet’s albedo2. For example, a 6% increase in the albedo of global marine stratiform clouds could offset the warming that would result from a doubling of atmospheric CO2 concentrations3. Marine warm cloud properties are thought to depend on aerosol levels and large-scale dynamic or thermodynamic states4, 5, 6. Here we present a comprehensive analysis of multiple measurements from the A-Train constellation of Earth-observing satellites, to quantify the radiative forcing exerted by aerosols interacting with marine clouds. Specifically, we analyse observations of co-located aerosols and clouds over the world’s oceans for the period August 2006–April 2011, comprising over 7.3 million CloudSat single-layer marine warm cloud pixels. We find that thermodynamic conditions—that is, tropospheric stability and humidity in the free troposphere—and the state of precipitation act together to govern the cloud liquid water responses to the presence of aerosols and the strength of aerosol–cloud radiative forcing.

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Thursday, July 7, 2011

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.
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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).
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