Monthly Archives: November 2008

What Are Climate Models? What Do They Do?

Originally posted on July 15, 2005.

Climate models are comprised of fundamental concepts and parameterizations of physical, biological, and chemical components of the climate system, expressed as mathematical formulations, and then averaged over grid volumes. These formulations are then converted to a programming language so that they can be solved on a computer and integrated forward in discrete time steps over the chosen model domain. A global climate model needs to include component models to represent the oceans, atmosphere, land, and continental ice and the interfacial fluxes between each other. Weather models are clearly a subset of a climate model (a discussion of mesoscale weather models is given in Pielke, R.A., Sr., 2002: Mesoscale meteorological modeling. 2nd Edition, Academic Press, San Diego, CA, 676 pp), where the basic framework of all scales of weather models is presented). On the global scale, it is very important to distinguish global atmospheric-ocean circulation models (AOGCMs) from global climate models. Global climate models need to include all important components of the climate system as discussed in a 2005 National Research Council report, while AOGCMs up the present have not.

There are three types of applications of these models: for process studies, for diagnosis, and for forecasting.

Process studies: The application of climate models to improve our understanding of how the system works is a valuable application of these tools. In an essay, I used the term sensitivity study to characterize a process study. In a sensitivity study, a subset of the forcings and/or feedback of the climate system may be perturbed to examine its response. The model of the climate system might be incomplete and not include each of the important feedbacks and forcings.

Diagnosis: The application of climate models, in which observed data is assimilated into the model, to produce an observational analysis that is consistent with our best understanding of the climate system as represented by the manner in which the fundamental concepts and parameterizations are represented. Although not yet applied to climate models, this procedure is used for weather reanalyses (see the NCEP/NCAR 40-Year Reanalysis Project).

Forecasting: The application of climate models to predict the future state of the climate system. Forecasts can be made from a single realization, or from an ensemble of forecasts which are produced by slightly perturbing the initial conditions and/or other aspects of the model. Mike MacCracken, in his very informative response to my Climatic Change essay seeks to differentiate between a prediction and a projection.

With these definitions, the question is where does the IPCC and US National Assessment Models fit? Since the General Circulation Models do not contain all of the important climate forcings and feedbacks (as given in the aforementioned 2005 NRC report) the models results must not be interpreted as forecasts. Since they have been applied to project the decadal-averaged weather conditions in the next 50-100 years and more, they cannot be considered as diagnostic models since we do not yet have the observed data to insert into the models. The term projection needs to be reserved for forecasts, as recommended in Figure 6 in R-225.

Therefore, the IPCC and US National Assessments appropriately should be communicated as process studies in the context that they are sensitivity studies. It is a very convoluted argument to state that a projection is not a prediction. The specification to periods of time in the future (e.g., 2050-2059) and the communication in this format is very misleading to the users of this information. This is a very important distinction which has been missed by impact scientists who study climate impacts using the output from these models and by policymakers.

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The Globally-Averaged Surface Temperature Trend – Incompletely Assessed? Is It Even Relevant?

Originally posted on July 11, 2005.

The globally-averaged surface temperature trend has been highlighted as an icon of climate change. For example, a meeting was held In Exeter, United Kingdom from Feb 1-3, 2005 entitled “Avoiding Dangerous Climate Change.” The focus on a globally-averaged temperature trend was clear in the emphasis at the meeting. The Hadley Centre brochure relevant to this meeting stated “Once a tolerable (i.e., non-dangerous) change has been determined – say in terms of a global temperature rise – we then have to calculate what this corresponds to in terms of tolerable greenhouse concentrations in the atmosphere.” The message is that a clear global surface temperature threshold exists over which there are dangerous effects on the climate system.

This perspective however, avoids discussing the real issue associated with long-term variability and changes in climate.

First, in the context of atmospheric circulation changes (which is, after all what produces our weather), it is the regional tropospheric temperature and humidity trends that are important, not a global average surface temperature A change in the globally-averaged surface, or even globally-averaged tropospheric, temperature are important primarily in the context of how this results in circulation changes. The globally-averaged surface temperature is a very poor metric to use to assess these circulation changes. The 2005 NRC report recognized this limitation in using globally-averaged surface temperatures. Secondly, with respect to even “global warming” the ocean heat content changes, rather than the surface temperature anomaly provides a more robust metric (see R-247).

With respect to the surface temperature itself, there are several issues with respect to the spatial representativeness of the trends that have been incompletely (or not at all) investigated. These are:

1. Poor microclimate exposure:
This is a land issue. The use of photographs to exclude questionable stations is obvious (and we are quite puzzled why anyone would not make this a high priority). The effect of poor exposure (which results in different site exposure depending on the wind direction) and changes in the site conditions over time have not been quantified. Our qualitative assessment based on the photographs that we have seen is that this it is likely to insert a warm bias for most sites. [Note added Nov 11 2008 see the outstanding summary of observation sites in Watts Up With That]
2. Moist enthalpy:
This is both a land and an ocean issue. The use of the terms “warming” and “cooling” are being incompletely used when there is significant water vapor in the surface air (tropics and mid-latitude warm seasons, in particular). This will produce a warm bias when the air actually became drier over time, and a cool bias when the air becomes more humid over time. This effect has not been quantified with respect to how it influences regional and global surface temperature trends. It has been shown to be significant for individual sites.
3. Vertical lapse rate issues (paper in preparation [noted added Nov 11 2008 : see the two papers which have appeared –  see and see)]:
The influence of different lapse rates, heights of observations and surface roughness have not been quantified. For example, windy and light wind nights should not have the same trends at most levels in the surface layer, even if the surface-layer averaged temperature trend was the same.
4. Uncertainty in homogeneity adjustments:
Time of observation, instrument changes, and urban effects have been recognized as important adjustments (see R-234) that are required to revise temperature trend information in order to produce improved temporal and spatial homogeneity. However, these adjustments do not report in the final homogenized temperature anomalies, the statistical uncertainty that is associated with each step in the homogenization process.

Thus even if the globally-averaged surface temperature was a particularly appropriate metric to assess climate change, there are issues on the robustness of this data set which have been overlooked. Our recommendation, however, is to deemphasize the globally-averaged surface temperature as a climate change metric and assess instead circulation changes as defined by tropospheric temperature and water vapor (and for the ocean, temperature and salinity) variability and trends.

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What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures?

Originally posted on July 28, 2005.

The 2005 National Research Council report concluded that:

“regional variations in radiative forcing may have important regional and global climate implications that are not resolved by the concept of global mean radiative forcing.”

And furthermore:

“Regional diabatic heating can cause atmospheric teleconnections that influence regional climate thousands of kilometers away from the point of forcing.”

This regional diabatic heating produces temperature increases or decreases in the layer-averaged regional troposphere. This necessarily alters the regional pressure fields and thus the wind pattern. This pressure and wind pattern then affects the pressure and wind patterns at large distances from the region of the forcing which we refer to as teleconnections.

The regional diabatic forcing can be caused by land-use/land-cover change (e.g. , Chase et al. 2000a) or by aerosol emissions. Even natural surface variations such as in ocean color produce such teleconnections in a general circulation model (see Atmospheric response to solar radiation absorbed by phytoplankton Shell et al. 2003)

There is debate, however, regarding whether the magnitude of the regional diabatic forcing is large enough to result in long distance teleconnections. However, observed multi-decadal trends in tropospheric-averaged temperatures are large enough to result in large-scale circulation trends (see, for example, A Comparison of Regional Trends in 1979-1997 Depth-Averaged Tropospheric Temperatures for the magnitude of the 1979-1997 regional trends). Thus land-use/land-cover changes and aerosol clouds that produce regional tropospheric temperature anomolies of a similar magnitude (or larger magnitude) would be expected to have significant teleconnection effects.

If this is true, than regional diabatic heating due to human activities represents a major, but under-recognized climate forcing, on long-term global weather patterns. Indeed, this heterogenous climate forcing may be more important on the weather that we experience than changes in weather patterns associated with the more homogeneous spatial radiative forcing of the well-mixed greenhouse gases (see the NASA press release, which is based on the multi-authored paper The influence of land-use change and landscape dynamics on the climate system: relevance to climate change policy beyond the radiative effect of greenhouse gases).

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What is Climate Change?

For the next several weeks Climate Science is reposting a number of weblogs that are worth repeating. We have quite a few more readers now than we did when my weblog started. The first reposting appears below.

Originally posted on July 29, 2005.

The different definitions of climate, have done much to confuse policymakers in the discussion of climate science.

The American Meteorological Society (AMS) definition of “climate change” is

“(Also called climatic change.) Any systematic change in the long-term statistics of climate elements (such as temperature, pressure, or winds) sustained over several decades or longer. Climate change may be due to natural external forcings, such as changes in solar emission or slow changes in the earth’s orbital elements; natural internal processes of the climate system; or anthropogenic forcing.”

The AMS defines anthropogenic forcing as

“Human-induced or resulting from human activities; often used to refer to environmental changes, global or local in scale.

The AMS defines the climate system as the

“system, consisting of the atmosphere, hydrosphere, lithosphere, and biosphere, determining the earth’s climate as the result of mutual interactions and responses to external influences (forcing). Physical, chemical, and biological processes are involved in the interactions among the components of the climate system.”

Here we have an inconsistency with the definition even by a very distinguished professional society! Climate, as defined by the AMS, is focused on the atmosphere, while the climate system consists of the atmosphere, hydrosphere, lithosphere, and biosphere. No wonder policymakers misapply this terminology.

As one example of the misuse by policymakers, the Royal Society released the following statement by Lord May:

“The science points to the need for a Herculean effort to make massive cuts in the amount of greenhouse gases that we pump into the atmosphere. So, while this encouraging new deal may play a role in this, it will only be part, and not all, of the solution.”

“But we have serious concerns that the apparent lack of targets in this deal means that there is no sense of what it is ultimately trying to achieve or the urgency of taking action to combat climate change. And the developed countries involved with this agreement must not be tempted to use it as an excuse to avoid tackling their own emissions.”

“All eyes should be on the United Nations Framework Convention on Climate Change in Montreal at the end of November [2005]. Top of the agenda at this meeting should be the initiation of a study into what concentration of greenhouse gases in the atmosphere we can allow without suffering the most catastrophic effects of climate change. This would allow us to plan cuts in worldwide emissions accordingly and provide direction to such efforts to tackle what is the biggest environmental threat we face today.”

Here the conclusion is made that to “combat climate change” we must initiate “a study into what concentration of greenhouse gases in the atmosphere we can allow without suffering the most catastrophic effectsof climate change.”

Ignored in this statement is the role of the other anthropogenic climate forcings that we identified in the National Research Council report.

Lord May, President of the Royal Society, has clearly overlooked a very critical definition of what really constitutes the climate system and what the anthropogenic forcings and feedbacks are that influence climate. He is, unfortunately, cherrypicking climate science.

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Holland Inundated: Another Opinion – Guest Weblog by Hendrik Tennekes

My weblog of October 28 stirred up quite some dust here in Holland. The Director-in-chief of KNMI was upset enough to send me an e-mail (the first ever!) explaining the official position of his institute. He wrote that KNMI supports the choice of 130 cm of sea-level rise as a worst-case estimate  based on the worst-case scenario of IPCC. I responded by writing that I felt it was his duty to declare in public that Professors Kabat and Vellinga had made  statements that go far beyond this extreme scenario, and were badly damaging legitimate concerns about climate change that way. He did not respond to that. I also sent him a draft of this second weblog, giving him the chance to respond or to prepare a weblog himself. He didn’t react to that either.

In the meantime, my mailbox was inundated. One Dutch climate scientist, who wishes to remain anonymous because of possible loss of job security, sent me the letter reproduced  below. I need not comment on the Climate of Fear apparently prevailing in the Dutch climate research community.

My respondent wrote: “I recently learned that there has been some debate about the contribution of KNMI, the Royal Netherlands Meteorological Institute, to the report by the Delta Commission. In this report, the Commission gives an estimate for the sea-level rise in the Netherlands in a “worst-case” scenario. Following the presentation of the report, two members of the Commission, Pavel Kabat and Pier Vellinga, stated that the sea level rise in this scenario – 130 cm rise in 2100 – is actually not a worst-case scenario, but a very likely one. This is a bit awkward, as you would think that everyone contributing to the report has agreed that this is actually a plausible-yet-very-unlikely scenario, and that by definition it cannot get worse than the worst possible case.”
“In a magazine interview, Pavel Kabat said: “I think we can easily reach or exceed 130 cm. We have given a cautious estimate of ice-cap meltdown. A new British study presents even higher figures.”  In an official lecture at Wageningen University, Pier Vellinga said: “It is very likely that we have to act within thirty years or less if we wish to prevent the Earth from warming up six to ten degrees in the next two centuries and the sea level from rising six meters or more.”
“Clearly, Kabat and Vellinga claim that the danger far exceeds the conclusions in the report to which they themselves have contributed. Normally you would expect that this would provoke an angry response from the other contributors. However, the Dutch climate research community has remained conspicuously silent. I would be willing to respect KNMI’s choice to remain silent, but only if everyone involved agrees that 130 cm is indeed an upper limit, based on a culmination of unfavorable scenarios. On its website, KNMI states that the policy with regard to coastal defense for the coming period continues to be based on the KNMI-2006 scenarios. KNMI  agrees on 130 cm as a plausible upper limit, but will adjust that number in the light of new observational evidence.”
“But how on earth are you going to validate the estimate of an upper limit? I would love to have explained in detail how we are going to establish, based on observations, whether or not the 130 cm is plausible. What methods, which observations, which time frames are required? By definition, validating something that is only a possibility is not possible beforehand. Since it is only a possibility it might not even occur.” 

“To complicate matters further, recent scientific publications show that we are not even capable of determining sea level rise during the last 5 years (2003-2007), while this is a period with by far the best available observations (Willis, JGR-oceans, 2008; Wunsch, J. Climate, 2008). Estimates range from zero rise to  3 mm/year; it is suggested in the literature that 3 mm might be an overestimation. These findings were recently  presented at a KNMI seminar. Yet no mention of these new findings anywhere.”
“KNMI could adopt another attitude. Take the KNMI or IPCC scenarios as starting point, and make very clear that these are the most likely results. Then take the scenario from the Delta-report – the background report indicates that even for the worst-case scenario the possibility exists of zero sea level rise despite the 6 degrees warming if all conditions are favorable – and draw the conclusion that it is simply not possible to derive anything meaningful from the worst-case scenario. It would have been possible that the worst-case scenario would have narrowed down uncertainties, but alas, that is not the case. This fact – the large uncertainty margin – could just as well be used to develop policy, a policy that can be adapted according to the progress of our knowledge and understanding. There are various possibilities for such a policy and there are plenty of scientists and researchers who promote developing these ideas.”

“I feel I have an obligation to warn society about people like Vellinga. I consider him dangerous because of his alarmism, his unfounded speculations about climate change, and his  misrepresentation of the findings in the Delta-report. Also, it would be good for the reputation of KNMI if it would adopt a more critical attitude. If KNMI does not accept and promote the idea that in the end it is all about truth, finding the truth, being objective and letting scientists be scientists, discussing and disagreeing with one another, then KNMI cannot be considered an independent scientific institute anymore. Independence and authenticity, that is what separates scientists from politicians or the common people.” 
That was my respondent’s reaction to the official position of KNMI. Like him, I am reluctantly willing to go along with 130 cm as an upper limit obtained by an accumulation of extreme assumptions, but only if no statements beyond that extremely unlikely scenario are tolerated. KNMI is in danger of losing its reputation as an authoritative scientific institution. As a retired KNMI research chief, I feel both ashamed and dismayed. 


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New Paper On Dynamic Downscaling Of Climate Models By Rockel Et Al. Published

Our paper

Rockel, B., C. L. Castro, R. A. Pielke, Sr., H. von Storch, and G. Leoncini (2008), Dynamical downscaling: Assessment of model system dependent retained and added variability for two different regional
climate models
, J. Geophys. Res., 113, D21107, doi: 10.1029/2007JD009461

has been published [this paper was also discussed on the Climate Science weblog of September 8 2008]

Our paper has wide significance on the claims made in reports, such as

“Climate Change in Colorado:  A Synthesis to Support Water Resources Management and Adaptation for the Colorado Water Conservation Board”by Andrea J. Ray, Joseph J. Barsugli, Kristen B. Averyt, Martin Hoerling, and Klaus Wolter,

that there is regional multi-decadal prediction skill. This is claim, however, is not supported by the scientific evidence.

As we conclude in our paper

 “We …. confirmed that dynamic downscaling does not retain (or increase) simulation skill of the large-scale fields over and beyond that which exists in the larger-scale model or reanalysis. Our conclusions should be relevant to all applications of dynamic downscaling for regional climate simulations.”

In other words, unless the global model has regional multi-decadal prediction skill (which has not been found; e.g. see

Koutsoyiannis, D., A. Efstratiadis, N. Mamassis, and A. Christofides, 2008: On the credibility of climate predictions, Hydrological Sciences Journal, 53 (4), 671-684. [weblogged on July 31 2008]

dynamic downscaling is not going to improve regional prediction skill to predict drought or other weather patterns.


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New Article In Physics Today Titled “A Broader View Of The Role Of Humans In The Climate System.”

Physics Today has just published an invited opinion piece

Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55.

The article starts with the text

“The 2007 report from the Intergovernmental Panel on Climate Change Working Group I presents a narrow view of the state of climate science. Attempts to significantly influence regional and local-scale climate based on controlling carbon dioxide emissions alone cannot succeed since humans are significantly altering the global climate in a variety of diverse ways beyond the radiative effect of CO2. The IPCC assessments have been too conservative in recognizing the importance of these human climate forcings as they alter regional and global climate. When the IPCC focuses its policy attention on CO2, it neglects other important aspects of the impact of human activities on climate.”

The conclusion of the article reads

 “Humans are significantly altering the global climate, but in a variety of diverse ways beyond the radiative effect of CO2. Significant, societally important climate change on the regional and local scales, due to both natural and human climate forcings, can occur due to these diverse influences. The result of the more complex interference of humans in the climate system is that attempts to significantly influence regional and local-scale climate based on controlling CO2 emissions alone is an inadequate policy for this purpose. There is a need to minimize the human disturbance of the climate by limiting the amount of CO2 that is emitted into the atmosphere by human activities, but the diversity of human climate forcings should not be ignored.”

The entire article can be read  at


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Is Climate Change A Co-Equal Threat As Global Urban Unemployment in the Future?

A remarkable news article appeared in The Times by Sean O’Toole with respect to global urban unemployment and crime entitled “The Big Picture: ‘It’s equal to climate change as a future threat’“.

A self-taught photographer David Lurie….[a]n old-school documentarian, using only black and white photography, he has in the past exhibited his stern photos under such heart-warming titles as “Struggling to Share the Promised Land”…… Lurie summarises his interest in the economically marginal communities at the centre of SA’s current crime wave with an analogy: “The global urban unemployment crisis is co-equal to climate change as a threat to our collective future.”

Lurie has a show with his photographs in South Africa as reported at the above website.

What is remarkable about his statement is the important and accurate message that there are major societal problems which need to be dealt with separate from climate.

However, the unfortunate message (or at least one that needs to be definitively shown) is the claim that climate change is equal to the threats posed by urban unemployment and crime.

Climate change means, of course, changes from the weather patterns of the past, and not climate variability that we have always experienced. With current and future societal changes, this climate variability might become more of a threat than in the past, but that is not what is meant by climate change (which is meant to be CO2 and other well-mixed greenhouse gas caused global warming).

The need to identify and prioritize risks to society and the environment is what we have emphasized in Part E of our book

Kabat, P., Claussen, M., Dirmeyer, P.A., J.H.C. Gash, L. Bravo de Guenni, M. Meybeck, R.A. Pielke Sr., C.J. Vorosmarty, R.W.A. Hutjes, and S. Lutkemeier, Editors, 2004: Vegetation, water, humans and the climate: A new perspective on an interactive system. Springer, Berlin, Global Change – The IGBP Series, 566 pp.) [(and see also)].

Bjorm Lomberg in his book Cool It: The Skeptical Environmentalist’s Guide to Global Warming comes to a similar conclusion. 

Climate assessments, such as performed by the IPCC and CCSP, have an obligation to quantitatively show why the role of human climate forcing (i.e. climate forcing”), with a specific focus on the emissions of CO2, has a higher or equal priority for available funds then other social and environmental threats (such as urban unemployment and crime).   There is also a need to separate the impacts of existing observed climate variability on the society of today and in the coming decades, from changes to these impacts from “climate change”.

We need recommendations for prioritizations that present a balanced framework, as discussed in

Pielke, Jr., R. A., 2007. The Honest Broker: Making Sense of Science in Policy and Politics. Cambridge University Press

which, unfortunately, was not adequately provided in the IPCC and CCSP assessments.

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Which is it? Trees Cool Or Heat the Planet? Studies Give Contradictory Results

Marc Morano has alerted us to an interesting contradiction with respect to how landscape affects the climate system which he headlines “Subject: Which is it? Trees Cool Or Heat the Planet? Studies Give Contradictory Results “.

His comment is illustrated by the two studies:

1. Northern Forests May Increase Temperatures by 10 Degrees by 2100, New Study Says; Deforestation Could Cool the Planet [April 9 2007]

This article includes the text

“Forests on certain parts of the planet may actually warm the Earth, according to researchers from the Lawrence Livermore National Laboratory in a study released today.

According to the study, forests in mid- to high-latitude locations — such as boreal forests of Canada, Scandinavia and Siberia — may actually create a net warming. The study concludes that by the year 2100, these mid- and high- latitude forests may make some places up to 10 degrees Fahrenheit warmer than would have occurred if the forests did
not exist.

The research, led by Lawrence Livermore National Laboratory atmospheric scientist Govindasamy Bala, appears in the April 9-13 online edition of the Proceedings of the National Academy of Sciences.”

2. Chemical released by trees can help cool planet, scientists find : Scientists discover cloud-thickening chemicals in trees that could offer a new weapon in the fight against global warming [October 31 2008]

 The text in this article states

“Trees could be more important to the Earth’s climate than previously thought, according to a new study that reveals forests help to block out the sun.

Scientists in the UK and Germany have discovered that trees release a chemical that thickens clouds above them, which reflects more sunlight and so cools the Earth. The research suggests that chopping down forests could accelerate global warming more than was thought, and that protecting existing trees could be one of the best ways to tackle the problem.

Dominick Spracklen, of the Institute for Climate and Atmospheric Science at Leeds University, said: ‘We think this could have quite a significant effect. You can think of forests as climate air conditioners.’

The scientists looked at chemicals called terpenes that are released from boreal forests across northern regions such as Canada, Scandinavia and Russia. The chemicals give pine forests their distinctive smell, but their function has puzzled experts for years. Some believe the trees release them to communicate, while others say they could offer protection from air pollution.

The team found the terpenes react in the air to form tiny particles called aerosols. The particles help turn water vapour in the atmosphere into clouds.

Spracklen said the team’s computer models showed that the pine particles doubled the thickness of clouds some 1,000m above the forests, and would reflect an extra 5% sunlight back into space.

He said: ‘It might not sound a lot, but that is quite a strong cooling effect. The climate is such a finely balanced system that we think this effect is large enough to reduce temperatures over quite large areas. It gives us another reason to preserve forests.’

The research, which will be published in a special edition of the Royal Society journal Philosophical Transactions A, is the first to quantify the cooling effect of the released chemicals. The scientists say the findings “must be included in climate models in order to make realistic predictions”.

What these two studies actually tell us is that

Humans can alter the Earth’s climate system in very signficant ways by changing the landscape. This important scientific conclusion has been essentially ignored in the IPCC and CCSP assessments.

An overview of this issue was reported on, for example, in

Pielke Sr., R.A., 2005: Land use and climate change. Science, 310, 1625-1626.


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