Showing posts sorted by relevance for query clouds models. Sort by date Show all posts
Showing posts sorted by relevance for query clouds models. 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, 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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Tuesday, December 31, 2013

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
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


Nature
 
505,
 
37–42
 
 
doi:10.1038/nature12829
Received
 
Accepted
 
Published online
 

Abstract

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.
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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.
...
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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Friday, August 30, 2013

New paper finds cloud assumptions in climate models could be incorrect by factor of 2

More problems for climate models: A new paper published in the Journal of Geophysical Research-Atmospheres finds that models must take into account not only the presence or absence of clouds but also how clouds are stacked vertically. The authors find that changes in vertical stacking of clouds can change radiative forcing assumptions by a factor of two [100%]. However, state of the art climate models do not take vertical stacking into consideration, and most global datasets of cloudiness also do not contain this information. "Clouds, which can absorb or reflect incoming radiation and affect the amount of radiation escaping from Earth's atmosphere, remain the greatest source of uncertainty in global climate modeling," and according to this paper, that uncertainty has just doubled from what was previously thought.

"There are known knowns; there are things we know that we know.
There are known unknowns; that is to say, there are things that we now know we don't know.
But there are also unknown unknowns – there are things we do not know we don't know."

 From today's AGU Journal Highlights:

 Atmosphere's emission fingerprint affected by how clouds are stacked

 Clouds, which can absorb or reflect incoming radiation and affect the amount of radiation escaping from Earth's atmosphere, remain the greatest source of uncertainty in global climate modeling.

 By combining space-based observations with climate models, researchers are able to derive baseline spectral signals, called spectral fingerprints, of how changes in the physical properties of the Earth's atmosphere, such as the concentration of carbon dioxide or the relative humidity, affect the amount of radiation escaping from the top of the atmosphere. Researchers can then use these spectral fingerprints to attribute changes in the observed top-of-atmosphere radiation to changes in individual atmospheric properties. However, recent research has shown that the way global climate models represent the interactions between clouds and radiation can complicate the process of making these spectral fingerprints. Researchers are finding that what matters is not only the presence or absence of clouds at each location represented in the model but also how the clouds are stacked vertically within each model grid.

 Using a simulation experiment to mimic the future climate, Chen et al. tested how different approaches to parameterize cloud stacking affect the attributions of climate change signals in the longwave spectra recorded at the top of the atmosphere. The authors tested three approaches to parameterize cloud stacking and find that the differences in stacking assumptions affected the modeled global mean for outgoing longwave radiation by only a few watts per square meter. The global average for outgoing longwave radiation at the top of the atmosphere is around 240 watts per square meter. However, based on which parameterization is used, similar changes in the portion of the sky covered by clouds (especially the clouds in the middle and lower troposphere) can lead to spectral fingerprints that differ by up to a factor of two in the amplitude.

 Source: Journal of Geophysical Research-Atmospheres, doi:10.1002/jgrd.50562, 
2013 http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50562/abstract

 Title: Non-negligible effects of cloud vertical overlapping assumptions on longwave spectral fingerprinting studies

 Authors: Xiuhong Chen and Xianglei Huang: Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA;
Xu Liu: NASA Langley Research Center, Hampton, Virginia, USA.

 ABSTRACT: In order to monitor and attribute secular changes from outgoing spectral radiances, spectral fingerprints need to be constructed first. Large-scale model outputs are usually used to derive such spectral fingerprints. Different models make different assumptions on vertical overlapping of subgrid clouds. We explore the extent to which the spectral fingerprints constructed under different cloud vertical overlapping assumptions can affect such spectral fingerprinting studies. Utilizing a principal component-based radiative transfer model with high computational efficiency, we build an OSSE (Observing System Simulation Experiment) with full treatment of subgrid cloud variability to study this issue. We first show that the OLR (outgoing longwave radiation) computed from this OSSE is consistent with the OLR directly output from the parent large-scale models. We then examine the differences in spectral fingerprints due to cloud overlapping assumptions alone. Different cloud overlapping assumptions have little effect on the spectral fingerprints of temperature and humidity. However, the amplitude of the spectral fingerprints due to the same amount of cloud fraction change can differ as much as a factor of two between maximum random versus random overlap assumptions, especially for middle and low clouds. We further examine the impact of cloud overlapping assumptions on the results of linear regression of spectral differences with respect to predefined spectral fingerprints. Cloud-relevant regression coefficients are affected more by different cloud overlapping assumptions than regression coefficients of other geophysical variables. These findings highlight the challenges in constructing realistic longwave spectral fingerprints and in detecting climate change using all-sky observations.

 Related: Climate models have been falsified at a confidence level of >98% over the past 15 years, and falsified at a confidence level of 90% over the past 20 years.
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Tuesday, June 17, 2014

New paper finds climate models simulate or predict only about 6% of altocumulus clouds

A paper published today in Atmospheric Research finds "Altocumulus clouds are important, yet climate models have difficulties in simulating and predicting these clouds" and "Approximately 93.6% of Altocumulus clouds cannot be resolved by climate models with a grid resolution of 1°."

Thus, only 6.4% of observed altocumulus clouds are simulated or predicted by climate models. Needless to say, clouds have profound effects on Earth's radiative balance and climate; a mere 1-2% change in global cloud cover alone can account for global warming or cooling. Among their many failings, climate models are unable to simulate clouds, ocean oscillations, solar amplification mechanisms, precipitation, sea ice, albedo, convection, etc. etc.

Spatial scales of altocumulus clouds observed with collocated CALIPSO and CloudSat measurements

•
Climatology of Ac horizontal scale and vertical depth is presented.
•
93.6% of Altocumulus clouds cannot be resolved by GCMs with a grid resolution of 1°.
•
Ac scale distributions are related to their formation mechanisms.
•
Ac vertical depth is impacted by CTT and environmental humidity.

Abstract

Altocumulus (Ac) clouds are important, yet climate models have difficulties in simulating and predicting these clouds, due to their small horizontal scales and thin vertical extensions. In this research, 4 years of collocated Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar and CloudSat radar measurements is analyzed to study the along-track horizontal scales and vertical depths of Ac clouds. Methodology to calculate Ac along-track horizontal scale and vertical depth using collocated CALIPSO and CloudSat measurements is introduced firstly. The global mean Ac along-track horizontal scale is 40.2 km, with a standard deviation of 52.3 km. Approximately 93.6% of Altocumulus clouds cannot be resolved by climate models with a grid resolution of 1°. The global mean mixed-phase Ac vertical depth is 1.96 km, with a standard deviation of 1.10 km. Global distributions of the Ac along-track horizontal scales and vertical depths are presented and possible factors contributing to their geographical differences are analyzed. The result from this study can be used to improve Ac parameterizations in climate models and validate the model simulations.
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Tuesday, June 10, 2014

New paper shows IPCC underestimates global cooling from man-made aerosols/clouds by factor of 27 times

According to a new paper published in Science, the global cooling effect of clouds nucleated by man-made aerosols since the beginning of the industrial revolution is approximately 15 watts per square meter, which is about 27 times more cooling effect than the mean estimate published in the 2014 IPCC AR5 Report:

Radiative forcing estimates from the 2014 IPCC AR5 Report show "cloud adjustments due to aerosols" since 1750 are a mean value of 0.55 watts per meter squared [+/-0.8] with level of confidence "low."
The IPCC-admitted "low confidence" and very poor representation of clouds/aerosols in climate models effectively renders IPCC climate model projections meaningless. The model projections have also been falsified at confidence levels of 95-98%.

 Aerosols that nucleate cloud formation can be from natural or man-made sources. For example, a recent paper published in Nature finds organic aerosols from pine trees may have a significant effect on cloud nucleation and cause global cooling. "Global brightening" from decreased aerosols/clouds over the past 30 years due to regulations on particulate emissions could also account for all or most of the observed warming over that period, instead of CO2. 

 A video in the E&E newswire article below demonstrates a dramatic cloud nucleation effect of the addition of small amounts of aerosols:


In the absence of aerosols, there can be no cloud nucleation. Scientists on an icebreaker in the Arctic demonstrated this in a video of a cup of hot tea that does not fume despite the below-zero temperatures. Then, someone flicks on a lighter and water vapor from the tea grabs aerosol particles emitted by the lighter (due to inefficient combustion) and a tiny storm appears, above the teacup. 

Researchers penetrate one of the darkest mysteries of climate change -- clouds

Gayathri Vaidyanathan, E&E reporter ClimateWire: Friday, June 6, 2014

Deadening calm fills the Horse Latitudes, where there's ocean, sky and little else. A satellite peers down, capturing wisps of cloud, counting particles suspended in the air, measuring rainfall and monitoring weather.

There is little wind. These latitudes, between 30 and 35 degrees away from the equator, are so calm that Spanish sailors in the 17th century could not move their heavily laden ships, or so the legend goes. So, the sailors dumped their cargo -- horses -- into the subtropical ocean and heaved on. But they left the place with a name: Horse Latitudes.

These windless tracts have yielded a new hypothesis relevant to climate science: Few clouds may have populated our skies before the Industrial Revolution, and pollutants spewed by factories since then may have vastly increased the cloudiness of our atmosphere. The results were published yesterday in the journal Science.

The finding cuts to the heart of uncertainty contained in climate models today. Most scientists agree that humans are releasing massive quantities of carbon dioxide into the atmosphere and causing global temperatures to rise. But they disagree on the rate of warming. A doubling of CO2 concentrations could warm the planet by between 2 and 4.5 degrees Celsius, according to the Intergovernmental Panel on Climate Change (IPCC).[actually, the latest IPCC report revised the lower bounds to 1.5C, not 2C]

Part of the uncertainty is due to clouds. They come in various shapes and types, as most people know -- puffy popcorns (cumulus); loose brush strokes of mostly ice (cirrus); towering, dark monsters of thunderstorms (cumulonimbus) and many others.

Clouds can either reflect the sun's incoming rays back into space, cooling the Earth. Or they can act as a sheath and trap heat close to the Earth's surface, warming the planet. Often, they do a little of both. And they do it incredibly well. Clouds have the ability to heat the planet much more than CO2, depending on the type of cloud, its geography and its altitude. And to make things more complicated, cloud particles can have various sizes, shapes and physical traits. Translating these into predictions about the overall effect of clouds on the climate can be quite difficult.

Replacing a simplistic view

Today's climate models do include clouds, but some types are better represented than others.

“Unfortunately, the climate system is very sensitive to little changes in clouds,” said Andreas Muhlbauer, research scientist at the Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington. He was not involved in the Science study. “So being off by just a bit in a climate model can have a significant impact on the ability to predict.”

Lumpy clouds (marine stratocumulus clouds) off the west coast of continents are well represented in climate models. The Science study unravels another cloud type -- the cumulus -- which some scientists say are poorly represented in climate models.

These clouds are so complicated that it can take a couple of days to explain them, said Ilan Koren, a planetary scientist at the Weizmann Institute of Science in Israel and lead author of the study, reached while en route to a Rolling Stones concert.

"I'm sorry, but there are no simple answers here," he said.

Koren and his colleague, Orit Altaratz, also a scientist at Weizmann, base their findings on a well-accepted theory -- that clouds grow rapidly in the presence of microscopic particles called aerosols. In the past, aerosols used to be mainly microscopic salt particles from the ocean, debris from volcanoes, organic material or bits of soil carried by the wind. Since the Industrial Revolution, black carbon and soot from our cars, factories and cook stoves constitute most of the cloud-forming aerosols.

Aerosols are key in whipping up a cloud, a process that begins with the sun. As the sun's rays hit the ocean, water evaporates into the gas phase. Water vapor attaches itself to aerosol particles floating in the air and condenses into a seed of water and dust that blooms into a full-fledged cloud that climbs up the sky.

In the absence of aerosols, there can be no cloud. Scientists on an icebreaker in the Arctic demonstrated this in a video of a cup of hot tea that does not fume despite the below-zero temperatures. Then, someone flicks on a lighter and water vapor from the tea grabs aerosol particles emitted by the lighter (inefficient combustion) and a tiny storm appears, above the teacup.

Adding just a little bit of pollution goes a long way toward cloud formation in a very pristine environment, said Muhlbauer of the University of Washington.

Computer models must wait for better data

"Ultimately, it [aerosols] affects the amount of clouds that are out there, and also the properties of the clouds -- the area, for example, they cover over the globe. And all that affects the radiation that can actually hit the [Earth's] surface," Muhlbauer said.

To demonstrate the aerosol effect, Koren and his colleagues observed clouds forming in the Horse Latitudes of the Southern Hemisphere. This region of the global oceans has little wind, which means pollutants are not easily carried over from continents. A few clouds may exist, but not too many given the aerosol-starved nature of the region.

The scientists used data from four different satellites to observe the clouds, the aerosol content, temperature, meteorology and rainfall over 92 days in the winter of 2007. They found that the skies became more overcast as the aerosol levels in the air increased naturally. And the effect did not cease; there was no point of saturation beyond which aerosols stopped affecting the clouds.

As the cloud cover doubled, they reflected more incoming solar rays back to space. Thus, the clouds had a cooling effect.

Koren and Altaratz hypothesized that the last time the skies were this clean of aerosols -- other than in the Horse Latitudes, that is -- was before the Industrial Revolution. The skies then must have been much less cloudy than today, Koren said.

An implication of this theory is that as these cumulus clouds became more widespread at the very beginning the Industrial Revolution could have cooled the Earth. Including these clouds in climate models could alter results significantly.
But there's no way to know for sure. No one maintained records of aerosol levels in preindustrial times, and for now, Koran's suggestion is mere speculation.

Muhlbauer said this was an "interesting" scenario but cautioned that the findings are extremely preliminary. Adding cumulus clouds into climate models is a "long way off," he said.

"That's going to be another 10 years at least."
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Saturday, May 18, 2013

New research implies climate is less sensitive to CO2 and sulfate aerosols

Extra cloud cover caused by emissions of sulphate aerosols is known to reduce global warming, but its impact in reducing temperatures has been overestimated in the climate models, new research from the Max Planck Institute has found. This research would in turn imply that climate sensitivity to CO2 has been overestimated in the climate models, since there would have to be less warming from CO2 offset by less cooling from sulphate aerosols. This also undermines Hansen's attempt to explain away the lack of global warming over the past 16 years due to sulphate aerosols. 


Clouds ‘Cool Earth Less Than Once Thought’

LONDON – Extra cloud cover caused by emissions of industrial pollutants is known to reduce the effects of global warming, but its impact in reducing temperatures has been over-estimated in the climate models, new research has found.
This is particularly significant for China and India, because it has been believed that these two giant countries would be partly shielded from the effects of climate change by their appalling industrial pollution. The Max Planck Institute for Chemistry in Germany believes this potential cooling effect has been exaggerated.
The Institute’s study looked at the behavior of sulphate particles in the air created by the reaction of oxygen with sulphur dioxide released from factory chimneys and other sources of pollution.
Extra cloud cover caused by emissions of industrial pollutants is known to reduce the effects of global warming, but its impact in reducing temperatures has been overestimated in the climate models.
Credit: Ave Maria Moistlik
In humid conditions the sulphates attract water droplets and form clouds. This increase in the cloud cover reflects more sunlight back into space and so cools the earth.
The Max Planck researchers went to study a cloud formed at the top of a mountain, taking samples at various times to see how the sulphates reacted progressively.  What was crucial was how the sulphates were formed in the first place.
Current climate models assume that hydrogen peroxide and ozone have a large role in creating the sulphates, but the new research shows that the catalysts for the chemical reaction are more likely to be metal ions like iron, manganese, titanium or chromium.
The key factor is that all of these are heavier than hydrogen peroxide and ozone, and because of this are more likely to fall out of the cloud through the pull of gravity, thus considerably reducing the cooling effect of the original pollution.

Less time aloft

Eliza Harris and Bärbel Sinha, with a number of other scientists, captured the air samples and examined the isotopes in a mass spectrometer.
Harris, who was recently awarded the Dieter Rampacher Prize as the youngest doctoral candidate of the Max Planck Society, said: “The relative reaction rates of isotopes are like fingerprints, which tell us how the sulphate was formed from the sulphur dioxide.”
“As my colleagues and I compared the basic assumptions of climate models with my results we were very surprised, because only one of twelve models considers the role of transition metal ions in the formation of sulphate,” said Harris, who is now working at the Massachusetts Institute of Technology (MIT) in the U.S.
Because of the extra size of the sulphates and hence their greater weight, compared with the previous assumptions, she believes that climate models have over-estimated the cooling effect of the sulphate aerosols by assuming they would stay airborne longer.
So far the findings have not been factored into calculations on the regional effect of climate change. Harris says that in Europe, where pollution from industrial processes is already on the decline, the change in the calculations on warming would be relatively small.
However, in the growing industrial giants like India and China, where coal-fired power stations and other forms of industrial pollution are throwing out sulphur dioxide at an ever-greater rate, then the effect could be considerable. Further research on this is continuing.
Paul Brown is a joint editor at Climate News Network. Climate News Network is a news service led by four veteran British environmental reporters and broadcasters. It delivers news and commentary about climate change for free to media outlets worldwide.



Sulfate aerosols cool climate less than assumed

Life span of cloud-forming sulfate particles in the air is shorter than assumed due to a sulfur dioxide oxidation pathway which has been neglected in climate models so far
May 14, 2013
Sulfur dioxide is as antagonist of greenhouse gases less effective than previously assumed. It forms sulfate aerosol particles in the air, which reflect sunlight, and as so-called cloud condensation nuclei influence the chemical processes within clouds. Therefore, sulfate aerosol particles help to cool the earth, making them an important factor in climate models. However, a team around researchers from the Max Planck Institute for Chemistry found out that it is likely most models overestimate the cooling effect of these particles. The reason is a largely disregarded reaction pathway catalysed by mineral dust within clouds, which has a strong influence on the life span of sulfate aerosol particles and their ability to reflect sunlight.
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Measurement Station Schmücke. HCCT 2010 (Hill Cap Cloud Thuringia 2010) - A ground-based integrated study of... [more]
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In their role as condensation nuclei, aerosol particles are an important trigger for the formation of clouds. As humidity accumulates on the particles droplets are formed, which later develop into clouds. Within the clouds, however, the chemical composition of these aerosol particles changes.
In order to find out exactly what happens within the clouds, Eliza Harris and Bärbel Sinha from the Max Planck Institute for Chemistry, together with other scientists form Mainz and further research institutes, investigated different air parcels. The special feature of their experiments was that they investigated a cloud which formed on top of a mountain. The scientists could therefore trace how the aerosol particles changed while the cloud was forming.

Analysis of isotopes shows how sulfate is produced

Eliza Harris’ main focus was the analysis of sulfur compounds. She investigated their composition in air samples which were collected at different times: Before the parcels entered the cloud, while they were in the cloud, and after they left the cloud.
The sulfur compounds in the samples differed in the distribution of sulfur isotopes. Isotopes are atoms of the same elements differing in the number of neutrons in the core and thus can be differentiated with the help of a mass spectrometer. The NanoSIMS ion microprobe, a highly sensitive mass spectrometer, enabled Harris to look into the chemical processes. “The relative reaction rates of isotopes are like fingerprints, which tell us how the sulfate was formed from the sulfur dioxide”, Eliza Harris explains her method, which was part of her doctoral research in the group of Peter Hoppe at the Max Planck Institute for Chemistry.

Role of transition metal ions in the formation of sulfate aerosols underestimated

Harris’ measurements showed that sulfate in clouds forms mostly through the oxidation of sulfur dioxide (SO2) by oxygen (O2). This reaction is catalysed by so-called transition metal ions (TMI) like iron, manganese, titanium or chromium. In addition, sulfate production mostly occurred in cloud droplets which formed on large mineral dust particles, the most important source of transition metal ions. Much less often the trail led to the oxidation of SO2 by hydrogen peroxide (H2O2) and ozone (O3). “As my colleagues and I compared the basic assumptions of climate models with my results we were very surprised, because only one of twelve models considers the role of transition metal ions in the formation of sulfate”, says the scientist, who is now working at the Massachusetts Institute of Technology (MIT) in the USA. Instead, most of the models used the alternative pathways of sulfur dioxide oxidation by hydrogen peroxide (H2O2), ozone (O3) and the hydroxyl radical (OH).
Sulfate produced catalytically through transition metal ions are formed on relatively large mineral dust particles, making them bigger than those formed through the reaction with hydrogen peroxide. Due to their size, they fall from the air at a faster rate – by force of gravity. The time frame for climate cooling by sulfate particles could therefore be shorter than has been believed.

A significant effect is expected in China and India

Eliza Harris assumes that the models have overestimated the climate cooling effect of sulfate aerosols. So far it is not quantifiable to what degree Harris’ discovery will impact climate prognoses. However, future models should consider the TMI catalysis reaction as an important pathway for the oxidation of sulfur dioxide, says the scientist. She thinks that the impact on climate models of European regions might probably be low, as mineral dust concentrations in the air are small and sulfur dioxide (SO2) emissions are declining. “In India and China, however, where sulfur dioxide emissions are expected to rise in the near future, combined with significantly higher concentrations of mineral dust in the air, the effect could be stronger”, assumes Harris. Future studies will show.
The study, which has been published in the journal Science (Vol…), was conducted in collaboration with the following institutes: the Max Planck Institute for Chemistry in Mainz, the Leibniz Institute for Tropospheric Research in Leipzig, the Department of Atmospheric Science at Colorado State University, the Earth System Science Research Centre at the Institute of Geosciences at the University of Mainz, and the Institute of Atmospheric Physics at the University of Mainz.
Eliza Harris was recently awarded the Dieter Rampacher Prize as youngest doctoral candidate of the Max Planck Society in 2012.

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