See the Tabbed Pages for links to video tutorials, and a linked list of post titles grouped by topic.

This blog is expressly directed to readers who do not have strong training or backgrounds in science, with the intent of helping them grasp the underpinnings of this important issue. I'm going to present an ongoing series of posts that will develop various aspects of the science of global warming, its causes and possible methods for minimizing its advance and overcoming at least partially its detrimental effects.

Each post will begin with a capsule summary. It will then proceed with captioned sections to amplify and justify the statements and conclusions of the summary. I'll present images and tables where helpful to develop a point, since "a picture is worth a thousand words".

Wednesday, May 30, 2012

Private Sector Investment in Renewable Energy and the Need for Federal Subsidies

Summary. Institutions in the private sector are actively implementing renewable energy projects that optimize energy efficiency, install local renewable energy facilities, and/or purchase energy that has been generated by renewable technologies.  Motivations for undertaking these projects include economizing on costs, reducing overall energy usage, and reducing fossil fuel use and emission of greenhouse gases.

In order to encourage these private sector activities, the U. S. federal government should maintain and expand subsidy support for renewable energy.  At the present time this support is contracting radically as the result of expiration of several short-term subsidy programs.  Respected authorities suggest expanding subsidy programs by three-fold, together with tailoring of subsidy programs to optimize effectiveness by, for example, stimulating strong competition and enhancing public-private consortia for deployment of renewable energy.

Introduction. Carbon Dioxide Emissions around the World.  The United States was the nation with the second highest rate of emissions of carbon dioxide (CO2) in the world in 2008 (the latest year tabulated by the U. S. Energy Information Agency (EIA)) .  It is predicted to remain second even by 2035.  Its rate of growth of emissions is foreseen as 0.3% per year, whereas that for China, the largest source of emissions, is expected to grow by 2.6% per year, assuming that no changes in emissions policies will be put in place.  Because of these differences in projected emission rates, by 2035 China is expected to emit 13,441 million metric tons (MMT) of CO2 (31% of the world’s emissions) while the U. S. is expected to emit 6,311 MMT (15% of the total).

Of the major emitters of CO2 in the world, the U. S. is the only one without a comprehensive legislated policy directed to the long-term management of its greenhouse gas emissions.  The state of California, by contrast (comprising about 13% of the economy of the entire country as of 2010), has implemented an ambitious, market-driven goal of reducing statewide emissions from all sources by 80% by 2050.  The European Union also has a plan in operation with the same objectives (see Energy Policy.  I. and Energy Policy. II.).  China differs from California and the European Union in not having a representative form of government, and in striving to expand its economy to a level comparable with that of already-developed countries.  Nevertheless it too has long term policies for its energy development covering the period of its 12th Five YearPlan for 2011-2015, and beyond.

Private Sector Investment in Renewable Energy.  A wide spectrum of corporate, governmental and nonprofit entities in the U. S. are undertaking significant programs that mitigate the effects of increased atmospheric greenhouse gases and the resulting increase in the long-term average global temperature.  This writer subscribes to an emailed newsletter from Environmental Leader (EL), which is distributed daily.  A nonrandom selection of items drawn from its emails between May 17 and May 24, 2012 is tabulated below in the Details section.  The entries are highly representative of offerings appearing routinely in the EL emails.  In general the projects are either energy efficiency efforts in preexisting structures, or installation of new renewable energy sources such as solar or wind energy.  The Environmental Defense Fund in collaboration with major American corporations, cities and colleges; Goldman Sachs Group; Wal-Mart; Apple; and the governments of the U. S. and the state of California are included in the tabulation.  It is significant that Goldman Sachs is committing US$40 billion over the next 10 years for renewable energy investment opportunities worldwide.

The projects highlight the fact that important segments of the American economy, drawn from the corporate, governmental and nonprofit sectors, are embarking on major projects that increase the efficiency of energy use in their facilities, and reduce reliance on energy derived from fossil fuels.  It is highly noteworthy that these efforts are being undertaken spontaneously, i.e., they are implemented on their own volition rather than in response to any particular governmental policy or imposed regulation.  Stated or implied motivations for these projects include savings in operating costs once a payback period is passed, the opportunity to reap profits from investments undertaken with third parties,  reducing greenhouse gas emissions to help mitigate long-term global temperature increases, and moving away from use of fossil fuels  (much of which originates abroad) for energy.

Subsidies for Renewable Energy.  The accumulation of greenhouse gases in the Earth’s atmosphere will continue indefinitely over the next several decades under current policies in place around the world.  This will lead to increased long-term global average temperature, and to its detrimental effects such as regional drought and heat waves, regionally increased rainfall and flooding, increased wildfires and decreased agricultural harvests.  For this reason it is imperative to implement measures to mitigate emissions as soon as possible.  The anecdotal initiatives in the private sphere mentioned here are representative of a broader trend occurring in the private sector in the U. S.  The availability and economic viability of various forms of renewable energy have benefited from financial support from the U. S. federal government over the past few decades; yet there have been serious problems with the way in which federal support has been implemented.

Subsidies for fossil fuels have been in place in the U.S. for almost 100 years.  Subsidies for the nuclear energy industry have been particularly profound.  Subsidies for renewable energy sources of course began much more recently.  Pfund and Healy recently reported on federal energy subsidies.  Historical average annual subsidies for sectors in the energy economy are shown below; the periods in question are in the caption of the graphic.  (Biofuels include agricultural ethanol.)  The cumulative subsidy for renewables (not counting biofuels) is less than one-tenth that for oil and gas.

Historical average of annual subsidies in 2010 US$ billions received by gray, oil and gas (US$4.86, over 1918-2009); purple, nuclear (US$3.50, over 1947-1999); orange, biofuels (US$1.08, over 1980-2009); green, renewable energy sources (US$0.37, over 1994-2009).

Separately, these authors conclude that, over the earliest 15 years of federal subsidy grants to a new technology, when their effects will have the greatest effect, nuclear energy received more than 1% of the federal budget (on a constant dollar basis), subsidies to the oil and gas industry amounted to one-half percent of the budget, whereas renewable energy sources received subsidies amounting to only about one-tenth percent of the budget.  Thus the proportional support for oil and gas in its early years as an industry was about 5 times greater than that for renewable energy sources.   Accordingly, in order to promote research, development and deployment (RD&D) of renewable energy sources, federal subsidies should be expanded proportionately.

In addition, for the renewable energy sector, recent subsidy support has occurred intermittently, interspersed with periods in which support lapsed.  This is shown for the case of wind energy in the following graphic, for an interval ending in 2006.

Cumulative wind generating capacity (left axis, blue line) and capacity added each year (right axis, green bars) for years from 1981 to 2006.  The arrows show years in which the Production Tax Credit (PTC)expired without being renewed.

The three arrows in the graphic above show years in which the Production Tax Credit lapsed rather than being continued without interruption.  This break in the continuity of support had a drastic effect, reducing the rate of installation of new wind generating capacity dramatically in the affected years (see the graphic above).  Corporate management needs to have an understanding of the economic environment to be expected over the medium and long term in order to make informed strategic and investment decisions.  Clearly the short-term intermittency of support for wind energy had major consequences in the corporate sector developing this energy source.

A new report from the Brookings Institution on present and future subsidy structures for renewable energy appeared in April 2012 (“Beyond Boom & Bust: Putting Clean Tech on a Path to Subsidy Independence” , by Jesse Jenkins, Mark Muro, Ted Nordhaus, Michael Shellenberger, Letha Tawney, and Alex Trembath).  Whereas Pfund and Healey’s report was retrospective, this document examines the present and allocated trends in the next few years.  They analyzed 92 distinct federal support programs.  They note that federal subsidies for renewable energy in 2012 contract to about 50% of the support in the previous year, and fall even further

U. S. Federal subsidy support for renewable energy 2009-2014 in US$ billions.  Red, non-stimulus support; Tan, stimulus (American Recovery and Reinvestment Act; ARRA) support.

by 2014.  The graphic shows that the recession stimulus for renewable energy, legislated in 2009 (beige segments above) fall to essentially zero by 2014, as intended.  Non-stimulus support for renewable energy (red segments) does not make up for the loss of the stimulus support, remaining at a very low level, about US$11-13 billion through 2014.
A schematic representation of the temporary nature of much federal support for renewable energy, as exemplified for wind and solar energy, is shown in the following graphic.  The specific labels for each arrow are understandably not legible; the important feature below is that many of the programs have terminated or are scheduled to terminate by 2013 (shown by the vertical bars at the ends of the respective arrows).  The various arrows identify specific statutory support programs. 

U. S. Federal subsidy support timelines for wind energy and solar energy through 2015 (the right-most vertical line in each panel) and beyond. 

For wind, the lowest arrow continuing beyond 2015 is for a loan guarantee program that continues until a budgeted maximum of US$1.5 billion for all renewables is reached.  For solar, the two lowest arrows continuing beyond 2015 are for a 30% investment tax credit through 2016 which falls to 10% after that, and for the same US$1.5 billion maximum described for the case of wind subsidies.

Jenkins and coworkers point out that many renewable energy companies are likely to experience market contraction, or undergo bankruptcy or consolidation, in the coming years.  This is expected in view of the reduced U. S. federal support currently envisioned, and because overseas markets for U. S. products are also contracting in view of loss of subsidy support abroad.  As did Pfund and Healey, Jenkins and coworkers recognize that U. S. federal support has been poorly conceived, characterized by a “boom and bust cycle of aid and withdrawal”.

On a positive note, however, they find that expenditures of US$150 billion between 2009 and 2014 likely leverage public and private investment in clean technology of US$327 to 622 billion.  Of course such investment levels bring with them significant expansion of jobs for the American economy.

The authors note that subsidy support should be wisely dispersed over the future term, to support renewable energy RD&D, manufacture and deployment during its sensitive formative period, recognizing that this sector faces formidable competitive stress from established fossil fuel-based energy and from foreign providers of renewable energy hardware that themselves are substantially subsidized.

They view the present period of diminishing subsidy support for renewables as a favorable opportunity to fashion purposeful, long-term support programs for this growing industry.  Among its recommendations for new policy departures are the following:

  1. Reward development of improved technologies, and promote cost reductions.  The market for renewable energy should remain a competitive one.  Deploying new technologies should be in market settings that provide incentives and rewards for continued improvements in technology performance and costs.  Subsidy programs should be structured for new developments arising as they proceed, by reducing or eliminating support for unsuccessful ventures and those that attain competitive stature on their own.  Use of private capital should be encouraged by subsidy programs, and support, while temporary, should be of sufficient duration that business ventures operate in an environment of financial certainty.
  1. The energy innovation system should strive to make renewable energy cheap.  RD&D should be expanded to three times today’s levels; Pfund and Healey reached a similar conclusion.  Federal programs such as Energy Frontier Research Centers, the Advanced Research Projects Agency-Energy, and Energy Innovation Hubs should be supported and expanded.  These typically are conducive to create public-private partnerships.  It is important to develop and utilize technical professionals of the highest level to help drive innovation.

We have provided anecdotal but representative reports of renewable energy and energy efficiency projects undertaken spontaneously in the private sector.  These show that more mature renewable energy technologies are competitive with energy derived from fossil fuels.  Deployment of non-fossil fuel-derived energy should be encouraged to expand this type of investment.

In the face of this stamp of approval provided in the private sector, U. S. federal support for renewable energy RD&D, manufacture and deployment is undergoing a drastic reduction at present.  We have summarized non-profit reports that strongly support expanding and optimizing federal government support for renewable energy.  Their recommendations should be implemented by the government.


Selections from Environmental Leader emails, detailing specific renewable energy projects, are tabulated below.


Company or Program
URL Link
Environmental Defense Fund Climate Corps
EDF places recent MBA and MPA graduates in 54 companies, universities and cities.  They identify ways to enhance energy efficiency, saving costs and lowering emissions.  Institutions include Google, Boeing, Boston City Schools, Los Angeles, New Orleans and Oberlin College.
Goldman Sachs Group
Goldman Sachs has identified renewable energy projects as a major investment opportunity over the next decade, having the potential for generating significant profit.  It plans to invest US$40 billion over the next 10 years, especially in major developing countries that have put aggressive programs in place to reduce greenhouse gas emissions, including China and Brazil.  It will target development of solar, wind, hydro, biofuels, biomass conversion, energy efficiency, energy storage, green transportation, efficient materials, LED lighting and transmission.
Goldman Sachs Group
Goldman Sachs intends to reduce its own net emissions of carbon dioxide to zero by 2020.
Central Concrete, A US Concrete company
Central Concrete will supply energy-efficient concrete to build the new San Francisco 49ers stadium, reducing CO2 emissions by 11,500 tons of CO2.  (Portland cement manufacture is very energy intensive; additionally CO2 is released from limestone when it is converted to the cement.)  Central uses coal fly ash in place of cement in its concrete.  It has in addition provided their concrete to San Francisco Public Utilities, NASA Ames Building, San Francisco Academy of Sciences, San Jose Arena, Stanford Stadium and Santa Clara University.
Deloitte Center for Energy Solutions
The Deloitte reSources 2012 Study is based on interviews with hundreds of business executives and 2,200 consumers.  90% of businesses have developed energy reduction goals, mainly electricity, for profitability and ethical reasons.  Customers of almost 2/3 of the companies also demand environmental solutions.  In the Study, companies have goals averaging 24% reduction in electricity, emissions, and fuel use over 3-4 years.  60% of companies have the goal of achieving pay-off of environmental investment of about 4 years.
Owens Corning
Owens Corning placed a solar photovoltaic (PV) system in operation at its Kearny, NJ facility in November 2009.  It was installed by SunEdison, with support from the American Recovery and Reinvestment Act.
The company’s Gresham OR plant opened its PV system in October 2009.  This system supplies 100% of the electric power for the plant. 
Owens Corning
Owens Corning is reducing emissions company-wide by 25% per unit of production, over 2006-2012.  In addition to PV systems, the company is optimizing its energy-intensive manufacturing of building materials.
Nissan is installing solar PV and solar thermal (for heat generation) panels at two vehicle assembly plants in Spain.
Apple will power its Maiden, NC data center 100% by renewable energy, 60% of which will be generated on site.  It has earned LEED Platinum certification.  Other facilities (including Austin, TX, Sacramento, CA, Cupertino, CA, Cork, Ireland, and Munich, Germany) are or will be powered by renewable sources.
Wal-Mart outlets in Massachusetts are being fitted with solar PV sources that will provide 10-15% of their power needs.  All together the projects will provide 10.5 MW of solar power at 27 stores.  Wal-Mart has similar projects in other states.  In California, for instance, 130 stores have or will have rooftop solar sources, generating 20-30% of their power needs.

Governmental Entities

Company or Program
URL Link
Environmental Defense Fund Climate Corps
EDF places recent MBA and MPA graduates in 54 companies, universities and cities.  They identify ways to enhance energy efficiency, saving costs and lowering emissions.  Institutions include Google, Boeing, Boston City Schools, Los Angeles, New Orleans and Oberlin College.
California Cap and Trade Program
The California Global Warming Solutions Act of 2006 (AB32) and governor’s executive order mandate prescribed, staged, reductions in statewide greenhouse gas emissions, to 80% by 2050.  As of now, the first auction of emission allowances will occur in November 2012, and emissions will be charged against allowances starting in January 2013.
U. S. Government & IBM
Under President Obama’s Executive Order 13514 to reduce energy use in federal buildings by 30% by 2015 from 2008 levels, IBM is providing “smart building technology”, first to some of the most-energy intensive facilities.  The technology permits monitoring and adjusting energy use to optimize efficiency.

Nonprofit Organization

Company or Program
URL Link
Environmental Defense Fund Climate Corps
EDF places recent MBA and MPA graduates in 54 companies, universities and cities.  They identify ways to enhance energy efficiency, saving costs and lowering emissions.  Institutions include Google, Boeing, Boston City Schools, Los Angeles, New Orleans and Oberlin College.

© 2012 Henry Auer

Thursday, May 10, 2012

Clouds Probably Amplify the Effects of Global Warming

Summary.  The New York Times published a report on the effects that clouds exert on long-term average warming of the globe.  Most climate scientists agree that clouds will have a neutral or a positive effect, i.e., one that acts to amplify the warming effect of the greenhouse effect and make it stronger.  The report identifies the work of Dr. Richard Lindzen as expressing the opposite view that cirrus clouds will act to reduce the effect of warming as the temperature rises.  This hypothesis is considered discredited among climate scientists.  To help understand this issue, this post provides background on the processes involving clouds and water vapor in the overall energy balance of the globe.

Introduction.  The role of water vapor and cloud cover in assessing the long-term warming of the earth  is complex, both with respect to observation (data gathering) and modeling.  A  schematic identifying the processes by which water vapor and clouds can affect the energy balance at the earth’s surface is shown below.

Processes involved in the global rate of absorbing or radiating energy due to clouds and water vapor.  Units are given in watts per square meter (W m-2), where 1 watt is a unit of power, i.e. a unit describing the rate of energy gain or loss per second.  The numbers given in the graphic represent the result of measurements and modeled calculation by the authors for March 2000 to May 2004. 
Darker yellow downward arrows, left, show incoming power per meter squared for visible solar light.  Paler yellow arrows, right, show outgoing power per meter squared due to heat (infrared) radiation, as well as heat radiation from the atmosphere back to the earth’s surface due to the greenhouse effect from CO2, water vapor and clouds.  Evapotranspiration (center) combines bulk evaporation and transport of water from the ground to the air by the transpiration of green plants.  Latent heat (cloud in center) is explained in this post
Source: Trenberth and coworkers, BAMS March 2009, pp. 311-323;
For sunlight reaching the earth, the sun's energy (visible light) is re-emitted as heat (infrared) energy. Water vapor is transparent to visible sunlight (just as is CO2), but water vapor and clouds act as greenhouse elements with respect to heat energy (also just as does CO2). As shown in the diagram, a) clouds directly reflect a portion of the visible light from the sun back into space, and b) clouds as well as atmospheric water vapor exert a greenhouse effect on heat (infrared) radiation originating at the earth’s surface.  This greenhouse effect absorbs a large portion of the heat and re-emits it in all directions, shown in the diagram as continuing on out into space and returning to the earth’s surface as heat. 

At the very bottom of the diagram, the net total result of the all the positive and negative contributions to the energy balance is shown as 0.9 W m-2, a small net warming effect.  It is important to see from this diagram that since this final result is a very small number arrived at by adding and subtracting very large numbers, any small error in the inputs will have a disproportionately large effect on the final result, and could easily turn a positive energy balance into a negative balance.  For example, even the reported outcome for the global average is the result of a cooling of 15.6 W m-2 for land (about 30% of the earth's surface) and a warming of 6.9 W m-2 for the oceans (about 70% of the surface).

The New York Times recently published a report discussing scientists’ current understanding of the role of clouds in the long-term increase in the global average temperature.  This involves new enhanced measurement methods as well as refined inputs into global climate models (GCMs; also general circulation models).  As noted above, clouds can contribute both to more cooling (reflection of incoming sunlight), and to warming (because clouds and water vapor contribute a greenhouse effect based on the heat (infrared) radiation leaving the earth’s surface).  According to the report, the broad conclusion of the great majority of scientists is that, in balance, a neutral or positive contribution to the overall global temperature dominates.  (Clouds are only one of many factors accounted for in GCMs.)

Background.  Climate scientists have reached a broad consensus that our planet is warming. By measuring the long-term average temperature at stations all around the globe, as well as by satellite in recent decades, they find that the global temperature is increasing, starting with the industrial revolution. Scientists attribute this warming to carbon dioxide, a greenhouse gas, that results from burning the fossil fuels that power global industrialization, as well as to other greenhouse gases produced industrially. These gases act to trap part of the heat radiation released by sunlight striking the surface of the earth that would otherwise escape into space. CO2 has been a component of the earth's atmosphere for millions of years. Yet its concentration has increased abruptly since the industrial revolution began due to mankind's burning of fossil fuels to provide energy.  The greenhouse effect that it exerts on the planet's climate has been enhanced as a result.

Of the CO2 that enters the atmosphere, a portion is absorbed by green plants as they grow (but is released as they die and decay), and a portion is absorbed into the waters of the oceans. The majority stays in the atmosphere for at least 100 years, or longer, as there is no additional mechanism that removes it. Before the industrial revolution the CO2 cycle was in equilibrium; the gas produced by animals and decaying vegetation was absorbed by the oceans and growing plants. But the carbon contained in fossil fuels is not recycled back to the geological reservoirs that the fuels came from. This carbon follows a one-way route from underground reservoirs to new, additional atmospheric CO2 once burned to supply energy.

Water is a greenhouse substance. Water also exerts a greenhouse effect, whether as water vapor (i.e., a gas) or a liquid (including droplets in clouds and fog). In this regard, atmospheric water differs in many ways from CO2. Its vapor concentration in air is much higher than that of CO2; at "room temperature" the capacity of water in air is about 25 parts per thousand (25,000 parts per million) whereas currently the content of CO2 is about 390 parts per million. For this reason, the greenhouse effect from atmospheric water is much stronger than that of atmospheric CO2. Without the greenhouse effect of water, ambient temperatures on the earth would be far below freezing. Second, locally the actual water vapor content can be anywhere from 0 to 100% of the upper limit (the relative humidity). Globally the long-term cycle of water between water vapor, clouds and fog, rain and snow, glaciers and groundwater, and the oceans remains at equilibrium, in the absence of global warming. But thirdly, the capacity of air to hold water vapor (as the gas) increases by about 7% per degree C (3.9% per degree F). Thus as the long-term global average temperature rises because of the CO2 greenhouse effect, the overall intensity of the global water cycle will grow.

The water cycle, including all the components mentioned above, is included in global climate models. The role played by clouds in various GCMs is modeled with different parameters. As shown in the graphic, some of the sunlight directly striking clouds, especially low clouds (cumulus) and middle, layered clouds (stratus), from space is reflected back into space as unaltered visible light. This reflected light never reaches the earth and does not contribute to the greenhouse effect. The highest (cirrus) clouds, however, are high enough to be formed of ice microcrystals rather than droplets of liquid water. It is believed that cirrus clouds permit most sunlight to pass through to the earth, in contrast to the behavior of lower clouds, while still retaining the ability to act as greenhouse elements, retaining a portion of the heat energy of re-emitted light.

Skeptics: Clouds will help cool the planet. The New York Times article devoted considerable emphasis to the views of certain scientist skeptics, especially the meteorologist Richard S. Lindzen of the Massachusetts Institute of Technology, affirming that clouds will contribute a cooling effect as the global temperature rises.  Dr. Lindzen has studied climate for more than five decades.  According to the Times, he believes that cirrus clouds, especially over the tropics, will serve as an “iris” (i.e. the portion of the mammalian eye, or of a camera, that regulates how much light reaches the retina, or the film) as the earth warms.  Warmer atmospheric temperatures, in his view, will lead to a thinning of cirrus clouds that will permit more heat (infrared) radiation to escape into space.  This negative effect on retention of heat will reduce the overall warming of the planet. 

The Times reports that these views have been warmly received by politicians and others, such as the Heartland Institute, who are skeptical of the role of CO2 and other greenhouse gases in the long-term warming of the planet.  According to the Times “most mainstream researchers consider Dr. Lindzen’s theory discredited”.  As an example, an article in 2009 by Trenberth and Fassulo , states “Many papers refute the negative feedback and iris hypothesis of Lindzen et al. [2001]”, citing as examples Hartmann and Michelsen, 2002,  “No evidence for iris”, Bull. Am. Meteorol. Soc., 83, 249–254; Randall et al., 2007, “Climate models and their evaluation”, in Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by S. Solomon et al., pp. 590– 662, Cambridge Univ. Press, New York; and evidence for a slight positive feedback by Lin et al., 2002, “The iris hypothesis: A negative or positive cloud feedback?”, J. Clim., 15, 3–7. 

The Times further reports that a paper published by Dr. Lindzen in 2009 included errors in data analysis that were identified by other scientists and subsequently affirmed by him.  In addition, a more recent manuscript was criticized by peer reviewers for a “prestigious American journal” and was rejected for publication.  This is significant (see this earlier post on this blog), since review by anonymous peers ensures that analysis and conclusions expressed are supported by the data (usually peer review does not assess the accuracy or validity of the data themselves).  Conversely, contemporary authors of journal articles thank their peer reviewers for offering constructive suggestions that improve the final form of the paper (for examples see Science 27 April 2012: Vol. 336 no. 6080 pp. 455-458, DOI: 10.1126/science.1212222 (see Acknowledgements); and Science 27 April 2012: Vol. 336 no. 6080 pp. 462-466; DOI: 10.1126/science.1218389 (see Acknowledgements)).

Other articles also assess cloud feedbacks.  NASA discussed (accessed May 5, 2012) long-term warming of the earth.  In addition to forecasting significant warming by the end of this century, this article states climate feedbacks could more than double predicted warming, including feedbacks “due to snow and ice, water vapor, clouds, and the carbon cycle.”  As the air warms, the ability of air to hold water vapor increases, as noted earlier.  As described above, clouds have both positive (greenhouse effect) and negative (reflection of sunlight) feedback effects on warming.  On balance, according to NASA, “most climate models predict a slight overall positive feedback or amplification of warming due to a reduction in low cloud cover.”
Discussing the role of cirrus clouds in this same post, NASA points out that they emit only small amounts of radiation because of their cold temperature.  Thus, being composed of (solid) water, cirrus clouds strongly absorb heat (infrared) radiation reaching them from below, and retain a significant fraction of that heat, leading to higher atmospheric temperature than would be the case if they were absent.  NASA states that in a world with higher average global temperatures, the air would have more water content that leads to formation of more cirrus clouds.  In this view CO2-induced greenhouse warming would be amplified by the presence of more heat-retaining cirrus clouds in the upper atmosphere. 

In a different post dated Dec. 13, 2010, NASA summarized work (accessed May 5, 2012) by Andrew Dessler of Texas A&M University that was scheduled to be published in the peer-reviewed journal Science.  Dessler identified a positive feedback effect on CO2-induced greenhouse warming arising from clouds, based on studies of data from 2000 to 2010 on low- and high-altitude clouds.  Dessler showed “that clouds amplify the warming we get from carbon dioxide.…The cloud feedback…does amplify the warming we get from greenhouse gases.”  His work also validates the ability of current GCMs to simulate observed cloud feedback effects reasonably well.

Clement and coworkers (see also a commentary by a nonparticipating scientist) analyzed the correlation of cloud cover (low- and mid-level clouds, excluding cirrus clouds) and sea surface temperature over a large portion of the northeast Pacific ocean at subtropical latitudes, using existing records, for the period 1952-2007.  In the region monitored there is a reduction in cloud cover when the sea surface temperature is warmer and vice versa.  This indicates that clouds interact with sea surface temperature in a way that amplifies warming.  The scientists then assessed whether existing GCMs in the archive of the worldwide consortium of climate scientists could reproduce their findings.  Only one of 18 models assessed succeeded in reproducing their findings in response to the warming induced by the known increase in greenhouse gases that occurred over this period.  

Trenberth and Fassulo, in the article mentioned earlier, published in 2009, modeled the effects of the complete cloud cover from 1950 to 2100 using all models in the worldwide archive.  Although they found considerable variation among models, some yielded projections for positive feedback effects from clouds, i.e., that increased surface temperatures would lead to effects on the cloud cover that amplified the increase.   


The New York Times published an article analyzing the effects of clouds on the warming of the planet.  It devoted considerable attention to skeptics who doubt that mankind’s activities and the greenhouse effect have led to long-term warming, and who have subscribed to the renegade view of Dr. Lindzen that cirrus clouds will act as an iris, releasing more heat energy to space as the earth warms. 

This post has presented background information showing that the contributions of clouds to the global climate are many, varied, and may be subject to considerable variability both in data analysis and in modeling their effects in GCMs.  It is important to understand that final effects are small numbers arrived at as the difference between large positive and negative contributions from individual processes.  Small changes in evaluating these processes can therefore lead to large changes in the final contribution, including changing from a net warming effect to a net cooling effect.

The consensus among the community of climate scientists is that the iris effect proposed by Dr. Lindzen is supported neither by experiment nor by GCM modeling.

© 2012 Henry Auer