Monthly Archives: May 2009

New Scientist Article “Land Clearances Turned Up The Heat On Australian Climate”

 There is a news article on the recent excellent MacAlpine research group papers

McAlpine, C.A., J. Syktus, J.G. Ryan, R.C. Deo, G.M. McKeon, H.A. McGowan, and S.R. Phinn, 2009:A continent under stress: interactions, feedbacks and risks associated with impact of modified land cover on Australia’s Climate. Global Change Biology, in press. doi: 10.1111/j.1365-2486.2009.01939.x

Deo, R. C., J. I. Syktus, C. A. McAlpine, P. J. Lawrence, H. A. McGowan, and S. R. Phinn, 2009: Impact of historical land cover change on daily indices of climate extremes including droughts in eastern Australia, Geophys. Res. Lett., 36, L08705, doi:10.1029/2009GL037666.

which have been weblogged on at Climate Science (see and see).

The news article in New Scientist on May 16 2009 is titled Land clearances turned up the heat on Australian climate and reads

“DEFORESTATION by European settlers may be to blame for making Australia’s drought longer, hotter and dryer than it would be otherwise.

The “big dry”, Australia’s 11-year drought, has been blamed on greenhouse gases and natural variability. To see if deforestation played a part, Clive McAlpine of the University of Queensland in Brisbane and colleagues used a climate model to simulate Australian conditions from the 1950s to 2003. They then compared the impact of today’s fragmented vegetation, obtained from satellite images, with that of 1788, prior to European settlement.

Over much of south-east Australia, where the drought has hit hardest, less that 10 per cent of the original vegetation remains. The team’s model showed that this land clearance has increased the length of droughts in the area by one to two weeks per year. In years of extreme drought, the loss of vegetation caused the number of days above 35 °C to increase by six to 18 days, and the number of dry days to increase by five to 15 days (Geophysical Research Letters, in press).

“Land clearing may be having a similar impact on the drought as greenhouse gases,” says McAlpine. Reforestation could minimise future droughts, he adds.

“It’s a nice piece of work,” says Andy Pitman of the University of New South Wales in Sydney, but he adds that the modelling needs to be confirmed.”

This excellent article highlights the role of land use change as a first order climate forcing. This climate forcing was inadequately reported on in the recent IPCC and CCSP climate assessments.

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Use Of 500 Mb Anomaly Plots As A Diagnostic To Assess Tropospheric Temperature Anomalies In Real Time

In the assessment of weather predictions, I routinely access the excellent website RAP Real-Time Weather Data. There is one product on this site that is quite informative with respect to tropospheric temperature anomalies on multi-decadal time scale, and it is their “500 mb Z-Anomaly” plots on their GFS model plots.

An example of one of the plots for a 120 hour forecast is given below.

A Northern Hemisphere perspective of these anomalies can be viewed at the Climate Prediction Center of NOAA (see). The contour interval for the 500 mb height anomalies is 120 m. The anomalies are departures from the 1979-95 daily base period means. Above average heights correspond to a warmer than average lower troposphere, while below average heights correspond to a cooler than average troposphere.

What is quite informative about these plots, if you follow them day by day over the year, is that the regions of above and below average 500 mb heights (which is what is displayed in these figures) has not shown evidence of any preference for more above average regions, as would be expected if the troposphere were significantly warming. 

Snapshots as given below, of course, represent “just weather”, but if we examine this data over time, we should be seeing a movement since 1979 towards more regions of above average heights, if the troposphere is warming. The relatively small warming that has been reported (e.g. see), is swamped by the much larger regional variations in warming and cooling.

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Brief Overview Of Several Climate Science Research Findings

Our research group and collaborating colleagues have published several papers with major findings with respect to climate science. This weblog lists several of these findings, along with the peer reviewed papers in which they are based on:

  • A conservative estimate of the warm bias resulting from measuring the temperature near the ground is around 0.21°C per decade (with the nighttime minimum temperature contributing a large part of this bias). Since land covers about 29% of the Earth’s surface, the warm bias due to just this one effect explains about 30% of the IPCC estimate of global warming. In other words, consideration of this one bias in temperature would reduce the IPCC trend to about 0.14°C per decade; still a warming, but not as large as indicated by the IPCC. [based on Lin, X., R.A. Pielke Sr., K.G. Hubbard, K.C. Crawford, M. A. Shafer, and T. Matsui, 2007: An examination of 1997-2007 surface layer temperature trends at two heights in Oklahoma. Geophys. Res. Letts., 34, L24705, doi:10.1029/2007GL031652; Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., and J.R. Christy, 2009: An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., submitted.] – for other uncertainties and biases in the monitoring of multi-decadal global average surface temperature trends; see).


  • From observations of the spatial distribution of the human input of aerosols in the atmosphere in the lower latitudes, the aerosol effect on atmospheric circulations (through their diabatic heating effect on the three dimensional pressure field), can be 60 times greater than the effect due to the radiative heating effect of the human addition of well-mixed greenhouse gases [based on Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974].


The acceptance of CO2 as a pollutant by the EPA , yet it is a climate forcing not a traditional atmospheric pollutant, opens up a wide range of other climate forcings which the EPA could similarly regulate (e.g., land use, water vapor). These other forcings, such as land-use change and from atmospheric pollution aerosols, may have a greater effect on our climate than the effects that have been claimed for CO2.

Our peer reviewed papers have not been refuted by any subsequent peer reviewed articles. Interested climate scientists are invited to contact me, if they are interested in posting a guest weblog as to what scientific reasons exist to reject any of the findings listed above.

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Filed under Climate Change Forcings & Feedbacks, Climate Change Metrics, RA Pielke Sr. Position Statements, Research Papers

Comments By Mike Smith of My Weblog “Debate Question For Professor Steve Schneider and Colleagues”

In response to my weblog Debate Question For Professor Steve Schneider and Colleagues Mike Smith and I have exhanged e-mails on these three hypotheses. With Mike’s permission, I have extracted the text from our e-mails and reproduced with minor edits below. 

Mike Smith is CEO of WeatherData Services, Inc., An AccuWeather Company.  Smith is a Fellow of the American Meteorological Society and a Certified Consulting Meteorologist.   He is a recipient of the American Meteorological Society’s Award for Outstanding Contributions to Applied Meteorology and WeatherData has received the Society’s Award for Outstanding Services to Meteorology by a Corporation.

Mike’s comments are in regular text, and mine are italicized.

Mike Smith’s first e-mail

Hi Roger,

I have been reading the exchange regarding the SF articles.  There is something I would like to circle back on.  You say, “only one of these is true” if I am reading you correctly,

1. The human influence is minimal and natural variations dominate
climate variations on all time scale;

2. While natural variations are important, the human influence is significant and involves a diverse range of first-order climate forcings (including, but not limited to the human input of CO2);

3. The human influence is dominated by the emissions into the atmosphere
of greenhouse gases, particularly carbon dioxide.

I do agree with you that, 30 years from now, when we know much more, likely only one of the three contentions will be the “most correct” answer.  But, I don’t believe we are at that point.

Given our current knowledge, why can’t the most likely answer be, “Somewhere between 1 and 2″?  I believe the current state-of-the- science is telling us #3 is not correct.  I agree with you that there are many human forcings that influence climate, but it is not clear to me that the Wichita heat island (which I have informally documented) or the Reno heat island (see Anthony Watts’ website) have much influence on world climate (i.e., would the climate in Rome or Honolulu be different if the RNO and ICT heat islands did not exist?).  Does the deforestation in Brazil influence the climate in South Africa? IF the answer is “no”, then on a planetary scale #1 is the correct answer.

My best educated guess is the most correct answer is about 70%  #1 and 30%  #2.  I realize you believe this answer would be incorrect. Please tell me where you think I am off base.    If you wish to publish this question and your answer, it would be fine.  I believe we gain with open debate.

Thanks and best wishes,


Roger A. Pielke Sr. Reply and Mike Smith’s further response

Hi Mike

 Thank you for your feedback. I agree that the three hypotheses need to be addressed with respect to scale. Our research (and that of others) indicates that there are well defined effects of land use/land cover change, the human input of aerosols including both changes in atmospheric concentrations and deposition, and biogeochemical effects due to added trace gases including CO2 on local and regional scales. From your e mail, it seems we both agree on this. If true, the first hypothesis is rejected for these spatial scales (as is the third hypothesis).

Mike Smith Response – I agree with this.

Roger A. Pielke Sr’s Comment

With respect to the global scale, the proper metrics include changes in atmospheric concentrations, alterations in circulation patterns, etc. There is no question that added CO2 is from human activities….

Mike Smith Response - I agree

Roger A. Pielke Sr’s Comment

……and this has altered the global average concentration of this gas.

Mike Smith Response

I agree, but I’m not sure we fully know the extent.  There is some evidence for natural variation in CO2 concentrations (i.e., do changes in ocean heat content significantly vary their contribution to atmospheric CO2 concentration?).

Roger A. Pielke Sr’s Comment

In terms of effects on circulations, there are now a number of papers that illustrate with models that there are changes due to several of the human climate forcings listed above.

Mike Smith Response

Yes, but are the models sufficiently robust to make this determination at this time?

Roger A. Pielke Sr’s Comment

I have concluded the first hypothesis is also rejected on the global scale, but agree this needs further investigation (models by themselves, of course, cannot be used to test hypotheses).

Mike Smith Response

I see your point and you may well be proven correct.  However, we seem to be in the early stages of testing the ‘natural variations’ hypothesis.  I am referring to the ‘blank sun.’  The very low levels of sunspot activity the last two years — which seems to be continuing — and which I would call a “natural” variation, may give us a chance to sort out natural from manmade forcings.  The IPCC has (I’m paraphrasing) rejected the hypothesis that variations in the sun’s output have a significant effect on earth’s climate.
The falling temperature trend since 1998 (and, at best, lack of warming in the oceans about which you have written extensively) that seems to parallel the fall in solar output will give us a chance to test several of these hypothesis, especially in view of the record (for modern times) levels of CO2 concentration.  We seem to be getting close to the point where the IPPC’s hypothesis (CO2 is the dominant forcing) is rejected if temperatures and ocean heat content continue to fall while CO2 levels continue to rise.

Other credentialed climate scientists are invited to e-mail me their comments also, and, if appropriate, they can also be posted as a guest weblog.

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New Article “Regional Climate Change In Tropical And Northern Africa Due To Greenhouse Forcing And Land Use Changes By Paeth Et Al 2009

Thanks to Jos de Laat of KNMI for alerting us to the paper

Paeth, H., K. Born, R. Girmes, R. Podzun, and D. Jacob, 2009: Regional Climate Change in Tropical and Northern Africa due to Greenhouse Forcing and Land Use Changes. J. Climate, 22, 114–132.

The abstract reads

“Human activity is supposed to affect the earth’s climate mainly via two processes: the emission of greenhouse gases and aerosols and the alteration of land cover. While the former process is well established in state-of-the-art climate model simulations, less attention has been paid to the latter. However, the low latitudes appear to be particularly sensitive to land use changes, especially in tropical Africa where frequent drought episodes were observed during recent decades. Here several ensembles of long-term transient climate change experiments are presented with a regional climate model to estimate the future pathway of African climate under fairly realistic forcing conditions. Therefore, the simulations are forced with increasing greenhouse gas concentrations as well as land use changes until 2050. Three different scenarios are prescribed in order to assess the range of options inferred from global political, social, and economical development. The authors find a prominent surface heating and a weakening of the hydrological cycle over most of tropical Africa, resulting in enhanced heat stress and extended dry spells. In contrast, the large-scale atmospheric circulation in upper levels is less affected, pointing to a primarily local effect of land degradation on near-surface climate. In the model study, it turns out that land use changes are primarily responsible for the simulated climate response. In general, simulated climate changes are not concealed by internal variability. Thus, the effect of land use changes has to be accounted for when developing more realistic scenarios for future African climate.”

Important findings from this paper include the text

 “….most investigations of future African climate change have been focused on the impact of increasing greenhouse gas (GHG) concentrations, which usually satisfy the effect of warmer tropical oceans but neglect the role of land cover changes (Pielke et al. 2002). Several of the GHG induced experiments from global climate models predict a northward extension of moisture advection into the Sahel zone and more humid conditions (Kamga et al. 2005; Hoerling et al. 2006), but still with little agreement between different climate models (Hulme et al. 2001; Maynard and Royer 2004; Coppola and Giorgi 2005; Cook and Vizy 2006; Paeth et al. 2008)…..”

“….Hence, the question arises whether the classical procedure of the IPCC, namely, the assessment of anthropogenic climate change by prescribing rising GHG and aerosol concentrations, is sufficient for the prediction of future African climate (Pielke et al. 2002). Another important factor for climate change, particularly in the low latitudes, may be the changing land cover in the form of land use changes owing to human activity like agriculture, shifting cultivation, pasture, urbanization, and transport infrastructure (Feddema et al. 2005). On the other hand, land cover changes as a natural response to climate change, like, for example, albedo changes in high latitudes, may be crucial in the extratropical regions. Regional studies for the United States, China, and Europe have shown that urbanization, land use changes, and vegetation loss may enhance the amplitude of near-surface warming considerably by up to a factor of 2 (Zhao and Pitman 2002). In tropical Africa, however, the effect on the hydrological cycle would be more relevant.”

“Several authors have suggested that the prevailing droughts during the second half of the twentieth century
were at least partly caused by land cover changes in tropical and subtropical Africa (Zeng and Neelin 2000; Pielke 2001; Semazzi and Song 2001; Zeng et al. 2002).”

This paper clearly documents a failure of the 2007 IPCC reports to include the assessment of the role of all first order climate forcings on the climate system.



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Debate Question For Professor Steve Schneider and Colleagues

The weblog

Comments On “The Global Warming Debates: Stephen Schneider” In The May 24 2009 Issue Of The Examiner.Com By Thomas Fuller

included a statement by Professor Steve Schenider that

If these guys think they are “winning” why don’t they try to take on face to face real climatologists at real meetings–not fake ideology shows like Heartland Institute–but with those with real knowledge–because they’d be slaughtered in public debate by Trenberth, Santer, Hansen, Oppenheimer, Allen, Mitchell, even little ol’ me. It’s easy to blog, easy to write op-eds in the Wall Street Journal.”

In the following, I propose a debate (on-line and in person) of the following:

  • The human influence is minimal and natural variations dominate climate variations on all time scale;
  • While natural variations are important, the human influence is significant and involves a diverse range of first-order climate forcings (including, but not limited to the human input of CO2);
  • The human influence is dominated by the emissions into the atmosphere of greenhouse gases, particularly carbon dioxide.

This question was orginally posed on the weblog

Three Climate Change Hypotheses – Only One Of Which Can Be True.

My postion is summarized in that weblog, as well as elsewhere; e.g. see

Pielke, R.A., 1998: Climate prediction as an initial value problem. Bull. Amer. Meteor. Soc., 79, 2743-2746.

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

Pielke Sr.,Roger A., 2008: A Broader View of the Role of Humans in the Climate System is Required In the Assessment of Costs and Benefits of Effective Climate Policy. Written Testimony for the Subcommittee on Energy and Air Quality of the Committee on Energy and Commerce Hearing “Climate Change: Costs of Inaction” – Honorable Rick Boucher, Chairman. June 26, 2008, Washington, DC., 52 pp.

with a detailed presentation in

Cotton, W.R. and R.A. Pielke, 2007: Human impacts on weather and climate, Cambridge University Press, 330 pp

and Chapter E in

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.

Since Steve Schneider is the Editor of the journal Climatic Change, he could publish a set of review papers which summarize the scientific evidence with respect to this issue.  He has used this mechanism before in his two paper series with Mike MacCracken and I;

Pielke Sr., R.A., 2002: Overlooked issues in the U.S. National Climate and IPCC assessments. Climatic Change, 52, 1-11.

MacCracken, M., 2002: Do the uncertainty ranges in the IPCC and U.S. National Assessments account adequately for possibly overlooked climatic influences. Climatic Change, 52, 13-23.

I encourage Steve to again use this venue to constructively advance the discussion of climate science.



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Response From Tom Fuller Of Examiner.Com

Yesterday, I posted a weblog with respect to an interview of Steve Schneider of Stanford University by Tom Fuller of (see). Mr Fuller replied last evening and his reply is posted below.

Update: Roger Pielke Sr., principal contributor to Climate Science, has commented both here and on his website regarding my classification of his weblog as a ‘skeptic’ weblog. I plead guilty to over-facile classification. Although Climate Science does regularly challenge the accepted wisdom of climate change activists, he is first and foremost a scientist who publishes regularly in peer-reviewed journals. As I have noted before here, one of the major themes pursued on Climate Science is that humans do influence the climate through deforestation, land-use policy and interruptions of the hydrologic cycle, and Pielke Sr. thinks that this may actually outweigh the effects of human emissions of CO2.

Mr. Pielke feels that being characterised as a skeptic is pejorative–and it is certainly used that way in many discussions. I guess I’ve developed a tough skin after being called much worse–to me it’s the use of the term denier that sets me off. But it’s essentially lazy writing, and I apologise. I actually have the highest respect for what I’ve seen of his work on his website and elsewhere.

I’ll be pursuing this further–sadly, Mr. Pielke didn’t provide an email address and the comments section of his blog are usually turned off. I will try and contact him but in the meantime, I apologise for any confusion.

Mr. Fuller also added in an e-mail to me (presented here with his permission),

“Dear Professor Pielke,

After reading your post (for the 4th time) on Climate Science, I wanted to talk briefly about my approach to the series of interviews I am conducting.

As a commentator (not a reporter), I am trying very hard to keep my opinion out of the discussions I have with my respondents. I do have strong views on the issue, but am trying to get a view of what people feel is the state of play at this point in time. If you do have the chance to look at some of my opinion pieces, you’ll see that I do try and balance the differing sides. For example,

My hope is that when the series is complete, people will be able to go through the list and find their own balance by comparing the differing views. I will also be providing my perspective later.

You may also publish this email if you think it adds anything to the discussion.


Tom Fuller”

I appreciate the clarification by Mr. Fuller of his plan to present a forum for the diverse perspective of views on climate science. This is long overdue from the media, and his contribution on this subject could be quite valuable and influential.

I have not heard back yet from Steve Schneider but will post his response if he sends and permits its posting.

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Comments On “The Global Warming Debates: Stephen Schneider” In The May 24 2009 Issue Of The Examiner.Com By Thomas Fuller

There is part one of an interview with Professor Stephen Schneider regarding global warming and climate change issues published on on May 24 2009. It is titled “The global warming debates: Stephen Schneider” and is written by Thomas Fuller who is the San Francisco Policy Environmental Policy Examiner reporter. This interview is an excellent example of the failure to present a balanced presentation of the climate science issues.

The reporter asked the following question

“More specifically, the principal skeptic websites (Watt’s Up With That, Climate Skeptic, Climate Audit and Climate Science) that I look at regularly seem to think they are winning the day. They think data is coming in that questions the established paradigm.”

First, the reporter erroneously presented my perspective as a “skeptic” website. 

Steve Schneider, unfortunately, chose not only to fail to correct this error, but demeaned the scientific value of these websites.

His reply is

“They have been thinking that as long as I have observed them and they have very few mainstream climate scientists who publish original research in climate refereed journals with them–a petroleum geologist’s opinion on climate science is a as good as a climate scientists opinion on oil reserves. So petitions sent to hundreds of thousands of earth scientists are frauds. If these guys think they are “winning” why don’t they try to take on face to face real climatologists at real meetings–not fake ideology shows like Heartland Institute–but with those with real knowledge–because they’d be slaughtered in public debate by Trenberth, Santer, Hansen, Oppenheimer, Allen, Mitchell, even little ol’ me. It’s easy to blog, easy to write op-eds in the Wall Street Journal.”

On the first issue, the characterization of my website as a “skeptic website” is completely inaccurate. In 2006, Andy Revkin of the New York Times also erroneously described me as a “climate skeptic”, and after confronting him on this mistake (see), the New York Time published a correction (see). My views on climate science, hardly those of a climate skeptic (which I consider a perjorative characterization of my perspective), are summarized, for example, in my weblogs

Summary Of Roger A. Pielke Sr’s View Of Climate Science

Roger A. Pielke Sr.’s Perspective On The Role Of Humans In Climate Change

Roger A. Pielke Sr.’s Perspective On Adaptation and Mitigation

and in my House subcommittee testimony in 2008; see

Pielke Sr., Roger A., 2008: A Broader View of the Role of Humans in the Climate System is Required In the Assessment of Costs and Benefits of Effective Climate Policy. Written Testimony for the Subcommittee on Energy and Air Quality of the Committee on Energy and Commerce Hearing “Climate Change: Costs of Inaction” – Honorable Rick Boucher, Chairman. June 26, 2008, Washington, DC., 52 pp.

More importantly, I am disappointed that Steve Schneider personally attacked the websites that are listed. I have quite a bit of respect for Dr. Schneider’s past work [e.g. his book Genesis Strategy is an excellent example of why we need a resource-based, bottom-up assessment of vulnerability, as has been discussed in our peer reviewed papers (e.g. see) and books (e.g. see)]. 

However, his casual denigration of each of the websites, Watt’s Up With That, Climate Skeptic, Climate Audit and Climate Science  (each of whose contributions to the discussion of climate science are informative and very valuable) represents a failure to engage in constructive scientific debate.

This cavalier dismissal of these websites illustrates that instead of evaluating the soundness of their scientific evidence, the authors of these websites, who provide a much needed broader viewpoint on climate science, are insulted. This is not the proper way to discuss scientific issues. 

I would be glad to debate Dr. Schneider (or any of the other individuals who are listed). 

I also challenge them to refute in the professional literature (and in a debate) the numerous peer reviewed articles and national (e.g. see) and international climate assessments (e.g. see) that present scientific evidence that conflicts with the narrow perspective on climate science that Steve Schneider is representing.  

For those interested in my scientific credentials in climate science, please see

Pielke Research Group

and my vita

Roger A. Pielke Sr.

I am alerting Dr. Schneider and Mr. Fuller to the appearance of my weblog on this subject, and will publish their replies with their permission, if they provide them.  

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Comments On A New Paper “Seasonal Climate Change Impacts On Evapotranspiration, Precipitation Deficit by Harmsen Et Al. 2009″

There is a new paper which presents forecasts of regional climate decades into the future. Climate Science has been very critical of such papers since i) we have wait decades to validate the skill of the predictions, and ii) the multi-decadal global climate models have shown no skill in predicting regional climate events (such as drought) in the 20th century up to the present (e.g. see

On the Credibility of Climate Predictions by Koutsoyiannis et al. 2008).

However, in contrast to many other such papers, this paper does recognize the serious limitations of this approach.

The paper is

Harmsen, E.W., Miller, N.L., Schlegel, N.J., Gonzalez, J.E., 2009: Seasonal climate change impacts on evapotranspiration, precipitation deficit and crop yield in Puerto Rico. Agricultural Water Management, 96, issue 7, 1085 – 1095,

with the abstract

“The purpose of this study was to estimate precipitation (P), reference evapotranspiration (ETo), precipitation deficit (PD = P − ETo) and relative crop yield reduction (YR) for a generic crop under climate change conditions for three locations in Puerto Rico: Adjuntas, Mayaguëz, and Lajas. Reference evapotranspiration was estimated by the Penman-Monteith method. Precipitation and temperature data were statistically downscaled and evaluated using the DOE/NCAR PCM global circulation model projections for the B1 (low), A2 (mid-high) and A1fi (high) emission scenarios of the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios. Relative crop yield reduction was estimated from a water stress factor, which is a function of soil moisture content. Average soil moisture content for the three locations was determined by means of a simple water balance approach.

Results from the analysis indicate that the rainy season will become wetter and the dry season will become drier. The 20-year average September precipitation excess (i.e., PD > 0) increased for all scenarios and locations from 121 to 321 mm between 2000 and 2090. Conversely, the 20-year average February precipitation deficit (i.e., PD < 0) changed from —27 to —77 mm between 2000 and 2090. The results suggest that additional water could be saved during the wet months to offset increased irrigation requirements during the dry months. The 20-year average relative crop yield reduction for all scenarios decreased on average from 12% to 6% between 2000 and 2090 during September, but increased on average from 51% to 64% during February. Information related to the components of the hydrologic water budget(i.e., actual evapotranspiration, surface runoff, aquifer recharge and soil moisture storage) is also presented. This study provides important information that may be useful for future water resource planning in Puerto Rico.”

The cavaets to this study are given in the section “Limitations in results presented”, where they write

“The results presented in this paper should necessarily be viewed with caution since they are based in part on coarse resolution GCM data downscaled to single sites. As Pielke et al. (2007) rightly point out, future ‘‘agricultural impacts extend far beyond a global mean temperature and include other anthropogenic climate forcings.’’ Some of these forcings include land-use change, atmospheric aerosols, and complex nonlinear feedbacks, not accounted for in present-day, and likely next-generation, GCMs. Statistical downscaling itself assumes that the predictor– predictand relationship remains constant in time with stationary dynamic conditions under future climate change (Mearns et al., 2003). Furthermore, this study was based on only one GCM and since many uncertainties still exist among different models, the results need to be used with caution (Bouraoui et al., 1997).”

A section in every paper of this type titled  “Limitations in results presented”, should be a requirement so that readers can more appropriately place such studies in ther proper perspective as “sensitivity studies”.

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Seminar On May 14 2009 By Roger A. Pielke Titled “Considering the Human Influence on Climate” At The George C. Marshall Institute

This past Thursday, May 14, 2009, I gave a presentation at the Army and Navy Club in Washington DC sponsored by the George C. Marshall Institute.

The talk is titled  “Considering the Human Influence on Climate” and the powerpoint slides are available (see). I appreciate the opportunity that the Marshall Institute provided to present my perspective on the climate issue, and to urge that independent assessments of climate science are very much needed.

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