I was interviewed in late Janaury 2010 by Maggie Koerth-Baker Of BoingBoing.net, but it was not used. The interview that did appear is at

Scientists hash out the uncertainties of climate sensitivity.

I was on travel, which is why she did not use it. As she explained in an e-mail on February 10 2010,

“I ended up having a few more questions than you were able to get into before you left. I ended up speaking by phone to Gavin Schmidt with NASA Goddard, as well as with Dr. Schwartz, who was able to clarify what he was trying to get at in the paper a little better than I understood it when I sent the questions to you.”

INTERVIEW of me by Maggie Koerth-Baker on Schwartz etl al, 2010: Why Hasn’t Earth Warmed as Much as Expected? Journal of Climate in press

Hi Ms. Koerth



Please see my answers below. Please let me know if you need further feedback. I recommend that you read our recent paper



Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union.

https://pielkeclimatesci.files.wordpress.com/2009/12/r-354.pdf



as a number of your questions are answered there also.



Best Regards



Roger



I’ve read over the paper by Dr. Schwartz. The questions I have for you are below. Please let me know if anything needs clarification, or if there’s anything that you’d like to talk with me about by phone.

1) It seems from reading the paper that Dr. Schwartz is arguing that the IPCC best estimate on the maximum GHG concentration in the atmosphere is not actually a good estimate–because it’s based on assumptions about climate

sensitivity and aerosol forcing that seem to be incorrect or, at least, that we don’t know enough about yet. Am I understanding this correctly? And, if so, do you agree with the conclusions of this paper?



I agree with the authors that forcing by anthropogenic aerosols.is incompletely understood. However, aerosols are only part of the climate forcings that we do not adequately understand. As we concluded in our paper



Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union.

https://pielkeclimatesci.files.wordpress.com/2009/12/r-354.pdf [all of the authors are Fellows of the American Geophysical Union]





“In addition to greenhouse gas emissions, other first- order human climate forcings are important to understanding the future behavior of Earth’s climate. These forcings are spatially heterogeneous and include the effect of aerosols on clouds and associated precipitation[e.g., Rosenfeld et al., 2008], the influence of aerosol deposition (e.g., black carbon (soot) [Flanner et al. 2007] and reactive nitrogen [Galloway et al., 2004]), and the role of changes in land use/land cover [e.g., Takata et al., 2009]. Among their effects is their role in altering atmospheric and ocean circulation features away from what they would bein the natural climate system [NRC, 2005]. As with CO the climate are estimated to be on multidecadal time scales and longer.”





The use of the global mean surface temperature (GMST), as the authors focus on in the paper, is also an inadequate metric to assess the sensitivity of the climate system to human and natural climate forcings and feedbacks that affect climate events such as drought, floods, etc.



In the National Research Council report



National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp. http://www.nap.edu/openbook/0309095069/html/



we concluded [where the global mean TOA (top of the atmosphere) radiative forcing is directly related to the GMST used the Schwartz et al paper] that



“…..the traditional global mean TOA radiative forcing concept has some important limitations, which have come increasingly to light over the past decade. The concept is inadequate for some forcing agents, such as absorbing aerosols and land-use changes, that may have regional climate impacts much greater than would be predicted from TOA radiative forcing. Also, it diagnoses only one measure of climate change—global mean surface temperature response—while offering little information on regional climate change or precipitation. These limitations can be addressed by expanding the radiative forcing concept and through the introduction of additional forcing metrics. In particular, the concept needs to be extended to account for (1) the vertical structure of radiative forcing, (2) regional variability in radiative forcing, and (3) nonradiative forcing. A new metric to account for the vertical structure of radiative forcing is recommended below.”





Thus, while the Schwartz et al paper is an important new research paper that presents evidence of current limitations in understanding and skillfully predicting the global average warming, it is just a step in addressing a much broader range of uncertainties in the climate system.



2) I was under the impression that current climate models matched up pretty well with observed historical changes in climate. This seems to say that that is not the case. Is that true?



The current climate models only have had some success with simulating the change of the global average surface temperature (the GMST) during the past century. They have not been able to skillfully predict any of the major long (or short) term extreme climate events that have occurred such as the 1930s dust bowl years in the central United States. Even for the GMST, they can only achieve realistic long term trends by imposing estimates of aerosol radiative forcings where they know the answer already. However, even then, as the Schwartz et al paper shows, our understanding of this aerosol forcing is still not completely understood. They even quote Jim Hansen to support this lack of understanding; i.e.



“Hansen (2008) has argued that “estimates of climate sensitivity based on the last 100 years of climate change are practically worthless, because we do not know the net climate forcing.”



3) I think most people understand what GHG are in everyday terms, but I want to get a better handle on aerosols. What’s a real-world example of something that would create the aerosols Dr. Schwartz’s paper is talking about?



The aerosols are created by industrial and vehicular emssions, biomass burning (e.g. forest and grassland fires), and dust from arid and semi-arid landscapes.



4) How do aerosols work to limit temperature increases?



Aerosols can work in both directions. Sulphates, for example, can reflect sunlight back into space that otherwise would warm the climate system. Soot (black carbon) can add to the warming of the atmosphere as it absorbs solar radiation that otherwise would be lost through reflection of sunlight back out into space.



The aerosols actually have a range of complex effects which are summarized in the NRC (2005; pages 34-44) report I listed above. They can even significantly alter cloud and precipitation processes directly. Table 2-2 on page 40 [http://www.nap.edu/openbook.php?record_id=11175&page=40] has a summary some of the aerosol effects.



5) I’m unfamiliar with “thermal disequalibrium”, can you explain what that means?



In reading the paper, it appears they refer to the time lag between when a radiative imbalance is applied and the GMST increases enough to remove this imbalance.



6) Is it, at this stage, unreasonable to make statements like, “xxx ppm means and xx increase in global temperature”? Why or why not?



This oversimplifies the complex response of the climate system to the diversity of human and natural climate forcings. If it were as simple as “xxx ppm means and xx increase in global temperature” we could explain the observed seasonal, annual and decadal averaged temperatures this way. However, as even the Schwartz et al paper with its focus on just one aspect of aerosol forcings show, the climate is more complicated than that.



7) Thermal lag is a possible factor in the temperature discrepancy. As I understand it, this has to do with the fact that the actual temperature increases and decreases caused by accumluating or mitigating GHG concentrations in the atmosphere don’t happen in synch….and, in fact, the temperature changes can happen years after the GHG changes. Can you explain for me a little about why this is?



The GMST responses to the radiative imbalance. There is a time lag if the system has inertia (due to its mass) such that the temperature takes a period of time to increase enough in order to remove this imbalance. This why, for example, it takes time for a pot of water to boil after we turn the burner on; there is a thermal lag. In the climate system, in order to diagnose the radiative imbalance and the thermal lag, all of the natural and human climate forcings must be accurately measured. The Schwartz et al paper shows that our knowledge of even the aerosol part is still significantly incomplete.



8) The paper talks about the possibility that natural variation in temperature may have increased since the beginning of the industrial era and, if so, that the natural variability would then account for more of the temperature discrepancy. Is there any way to know whether natural variation has increased?



This is a topic of considerable debate. There has been recent research that indicates a greater solar climate forcing than previously understood. The alterations in the atmospheric circulation patterns over year and longer time periods also appears to result in larger natural variability in the GMST than previously thought. However, it is a challenge to ferret out the human from the natural forcings as the response of the climate system, such as the GMST, is the net result of this range of forcings and resultant climate feedbacks.



9) If Dr. Schwartz is correct, and if climate sensitivity isn’t as strong as is currently assumed, what does that mean? Do we have more time to counteract climate change? Do we just not know how much time we have?



In our EOS article we wrote



“The evidence predominantly suggests that humans are significantly altering the global environment, and thus climate, in a variety of diverse ways beyond the effects of human emissions of greenhouse gases, including CO2. Unfortunately, the 2007 Intergovernmental Panel on Climate Change (IPCC) assessment did not sufficiently acknowledge the importance of these other human climate forcings in altering regional and global climate and their effects on predictability at the regional scale. It also placed too much emphasis on average global forcing from a limited set of human climate forcings. Further, it devised a mitigation strategy based on global model predictions. Although aerosols were considered as a global average forcing, their local effects were neglected (e.g., biomass burning, dust from land use/land cover management and change, soot from inefficient combustion).



Because global climate models do not accurately simulate (or even include) several of these other first- order human climate forcings, policy makers must be made aware of the inability of the current generation of models to accurately forecast regional climate risks to resources on multidecadal time scales. For example, how the water cycle responds to the diversity of climate forcings at the regional level will be important information to policy makers seeking to mitigate risks to water resources.



We recommend that the next assessment phase of the IPCC (and other such assessments) broaden its perspective to include all of the human climate forcings. It should also adopt a complementary and precautionary resource- based assessment of the vulnerability of critical resources (those affecting water, food, energy, and human and ecosystem health) to environmental variability and change of all types. This should include, but not be limited to, the effects due to all of the natural and human caused climate variations and changes.”



10) What parts of climate science do we have a good certainty level on? Does the situation boil down to, “We know anthropogenic climate change is happening, but we have no idea of the rate of change?”



We concluded in our EOS article that



“Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first- order climate forcings, including, but not limited to, the human input of

carbon dioxide (CO2). Most, if not all, of these human influences on regional and global climate will continue to be of concern during the coming decades.”



and made the recommendation that



“If communities are to become more resilient to the entire spectrum of possible environmental and social variability and change [Vörösmarty et al., 2000], scientists must properly assess the vulnerabilities and risks associated with the choices made by modern society and anticipate the demands for resources several decades into the future. Moreover, since the climate, as a complex nonlinear system, is subject to abrupt changes and driven by competing positive and negative feedbacks with largely unknown thresholds [Rial et al., 2004], scientists’ ability to make skillful multidecadal climate predictions becomes much more complicated, if not impractical.”



11) Should people trust climate predictions/scenarios at this point? Are people ascribing too much confidence to those predictions?



Yes; there is too much reliance on these predictions. We recommend an approach based on the assessment of vulnerabilities to our key resources of water, food, energy, human health and ecosystem function as we wrote in our EOS article.



12) What will it take to better understand the impact of aerosols? How much money and effort is currently directed at this part of climate science?



There is quite a bit of funding on aerosol research. Where we need more funds and effort is in identifying the vulnerabilities to the key resources and then to seek solutions to reduce the threats to them.



13) Does the fact that aerosols may be limiting temperature increases due to GHG mean that we need to find a way to cut GHG emissions while simultaneously not reducing aerosol emissions?



We need a much broader assessment of the role of humans in the climate system. We are finding out, as the Schwartz et al paper illustrates, that as we learn more about the climate system, we are finding that it is more complex and difficult to skillfully predict than was assumed in the past.