Monthly Archives: August 2007

Advocacy In The Guise Of Climate Science – A New Paper That Exemplifies This Approach

There is a new paper that presents a claim that the Earth’s climate system is dominated by positive radiative feedbacks, and that includes the heading in section of the paper “Planet Earth today: imminent peril”. This sensationalism, however, in the view of Climate Science, is unsubstantiated by examining even the most basic of measures, where if the 2007 values of the IPCC radiative forcing are accepted, and the observed ocean heat storage data is used to diagnose what has been the sum total of real world radiative forcings and feedbacks in the last few decades, the climate feedbacks have been negative (as is discussed below)! This contradicts the fundamental premise of the paper

Hansen, J., M. Sato, P. Kharecha G. Russell, D. W. Lea, M. Siddall, 2007: Climate change and trace gases; Phil. Trans. R. Soc. A (2007) 365, 1925–1954 doi:10.1098/rsta.2007.2052 Published online 18 May 2007.

The abstract reads,

“Palaeoclimate data show that the Earth’s climate is remarkably sensitive to global forcings. Positive feedbacks predominate. This allows the entire planet to be whipsawed between climate states. One feedback, the ‘albedo flip’ property of ice/water, provides a powerful trigger mechanism. A climate forcing that ‘flips’ the albedo of a sufficient portion of an ice sheet can spark a cataclysm. Inertia of ice sheet and ocean provides only moderate delay to ice sheet disintegration and a burst of added global warming. Recent
greenhouse gas (GHG) emissions place the Earth perilously close to dramatic climate change that could run out of our control, with great dangers for humans and other creatures. Carbon dioxide (CO2) is the largest human-made climate forcing, but other trace constituents are also important. Only intense simultaneous efforts to slow CO2 emissions and reduce non-CO2 forcings can keep climate within or near the range of the past million years. The most important of the non-CO2 forcings is methane (CH4), as it causes the second largest human-made GHG climate forcing and is the principal cause of increased tropospheric ozone (O3), which is the third largest GHG forcing. Nitrous oxide (N2O) should also be a focus of climate mitigation efforts. Black carbon (‘black soot’) has a high global warming potential (approx. 2000, 500 and 200 for 20, 100 and 500 years, respectively) and deserves greater attention. Some forcings are especially effective at high latitudes, so concerted efforts to reduce their emissions could preserve Arctic ice,
while also having major benefits for human health, agricultural productivity and the global environment.”

One statement in the conclusion reads,

“Earth’s climate is remarkably sensitive to forcings, i.e. imposed changes of the planet’s energy balance. Both fast and slow feedbacks turn out to be predominately positive. As a result, our climate has the potential for large rapid fluctuations. Indeed, the Earth, and the creatures struggling to exist on the planet, have been repeatedly whipsawed between climate states.”

This is obviously an erroneous statement! If all of the feedbacks were predominately positive, the climate would long ago evolved to a a very extreme state. This clearly has not occurred, and such statements in this article are unsubstantiated scientifically in the paper, and, even more importantly, fail to represented the dynamics of the current climate system, where, as has been summarized on Climate Science, the net effect of all of the feedbacks, assuming the 2007 IPCC estimate of climate forcings is correct, is negative!

That the feedbacks must be negative in recent years (or the 2007 IPCC net forcing is in error) is discussed in

The Net Climate Feedbacks Must Be A Negative Effect On The Global Average Radiative Imbalance If The IPCC Conclusion Of Net Anthropogenic Radiative Forcings Is Correct.

Just two excerpts from the paper are needed to recognize what the Hansen et al paper is all about, i.e.

“The Arctic epitomizes the global climate situation. The most rapid feasible slowdown of CO2 emissions, coupled with focused reductions of other forcings, may just have a chance of avoiding disastrous climate change.”

and

“The potential of these ‘amber waves of grain’ and coastal facilities for permanent underground storage ‘from sea to shining sea’ to help restore America’s technical prowess, moral authority and prestige, for the sake of our children and grandchildren, in the course of helping to solve the climate problem, has not escaped our attention.”

This paper is clearly an advocacy article using the guise of cherrypicked science to promote a particular political and policy agenda. It very much fits into the definition of “stealth issue advocacy” as discussed in

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

The Hansen et al paper is clearly not an example of serving as an honest broker of climate science.

Hansen et al, of course, are correct that the climate system is nonlinear and sudden transitions on a variety of space and time scales do occur, as we discussed in

Rial, J., R.A. Pielke Sr., M. Beniston, M. Claussen, J. Canadell, P. Cox, H. Held, N. de Noblet-Ducoudre, R. Prinn, J. Reynolds, and J.D. Salas, 2004: Nonlinearities, feedbacks and critical thresholds within the Earth’s climate system. Climatic Change, 65, 11-38.

The Hansen et al article, however oversimplifies the climate system as being dominated by the radiative effect of human added CO2. Such a perturbation, of course, just as easily could move us away from undesirable climate transitions, instead of toward such transitions. Prudence suggests that we work to minimize our disturbance of the climate system since we do not understand the climate system well enough.

However, to focus on just a small subset of forcings is seriously misleading policymakers on the most effective way to deal with our social and environmental vulnerability from the entire spectrum of the actual environmental risks and other threats that we face.

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Deferred Forecasts Of Global Warming – An Example Of The Misuse of Science

A blatant example of masking an untested hypothesis as a scientific paper has been published in Science. The paper is

“Improved Surface Temperature Prediction for the Coming Decade from a Global Climate Modelâ€? Doug M. Smith, Stephen Cusack, Andrew W. Colman, Chris K. Folland, Glen R. Harris, and James M. Murphy (10 August 2007) Science 317 (5839), 796. [DOI: 10.1126/science.1139540].

The abstract reads,

“Previous climate model projections of climate change accounted for external forcing from natural and anthropogenic sources but did not attempt to predict internally generated natural variability. We present a new modeling system that predicts both internal variability and externally forced changes and hence forecasts surface temperature with substantially improved skill throughout a decade, both globally and in many regions. Our system predicts that internal variability will partially offset the anthropogenic global warming signal for the next few years. However, climate will continue to warm, with at least half of the years after 2009 predicted to exceed the warmest year currently on record.â€?

The August 9, 2007 Reuters reports on this article by writing

“Global warming is forecast to set in with a vengeance after 2009, with at least half of the five following years expected to be hotter than 1998, the warmest year on record, scientists reported on Thursday.

Climate experts have long predicted a general warming trend over the 21st century spurred by the greenhouse effect, but this new study gets more specific about what is likely to happen in the decade that started in 2005….

The real heat will start after 2009, they said.”

This is a very convenient and clearly contrived presentation to defer the expectation that significant global warming will occur for a few years, so that the particular policy actions (on energy policy as concluded on Climate Science; e.g. see) can occur.

The UK Met Office had a press release on this paper on August 10, 2007 titled

“The forecast for 2014…”

They write in this press release,

“These predictions are very relevant to businesses and policy-makers who will be able to respond to short-term climate change when making decisions today. The next decade is within many people’s understanding and brings home the reality of a changing climate.”

However, no one has shown any predictive skill on this time scale! That Science published this article speaks more for their use of this forum for advocacy, rather than as a science paper. Policymakers are bing misled if they accept that this prediction is skillful.

Climate Science has presented documentation on the inability of the multi-decadal global models to make skillful predictions (e.g. see and see, as just two examples).

Readers of paper such as Smith et al should recognize that the publication of climate process studies as predictions is misleading. Such predictions are just hypotheses, which can be tested only after the time period has passed.

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More On Another Climate Forcing Effect – Ozone

There is a paper in Nature which discusses an effect of increased ozone on the carbon assimilation and release into the atmosphere. The paper is

S. Sitch, P. M. Cox, W. J. Collins and C. Huntingford, 2007: Indirect radiative forcing of climate change through ozone effects on the land-carbon sink, Nature 448, 791-794 (16 August 2007) | doi:10.1038/nature06059; Received 9 September 2006; Accepted 3 July 2007; Published online 25 July 2007

The abstract reads,

“The evolution of the Earth’s climate over the twenty-first century depends on the rate at which anthropogenic carbon dioxide emissions are removed from the atmosphere by the ocean and land carbon cycles. Coupled climate–carbon cycle models suggest that global warming will act to limit the land-carbon sink, but these first generation models neglected the impacts of changing atmospheric chemistry. Emissions associated with fossil fuel and biomass burning have acted to approximately double the global mean tropospheric ozone concentration, and further increases are expected over the twenty-first century. Tropospheric ozone is known to damage plants, reducing plant primary productivity and crop yields, yet increasing atmospheric carbon dioxide concentrations are thought to stimulate plant primary productivity. Increased carbon dioxide and ozone levels can both lead to stomatal closure, which reduces the uptake of either gas, and in turn limits the damaging effect of ozone and the carbon dioxide fertilization of photosynthesis6. Here we estimate the impact of projected changes in ozone levels on the land-carbon sink, using a global land carbon cycle model modified to include the effect of ozone deposition on photosynthesis and to account for interactions between ozone and carbon dioxide through stomatal closure. For a range of sensitivity parameters based on manipulative field experiments, we find a significant suppression of the global land-carbon sink as increases in ozone concentrations affect plant productivity. In consequence, more carbon dioxide accumulates in the atmosphere. We suggest that the resulting indirect radiative forcing by ozone effects on plants could contribute more to global warming than the direct radiative forcing due to tropospheric ozone increases.”

This paper clearly identifies a new interaction among the components of the climate system.

The paper, however, neglects to also discuss the role of added ozone in altering the surface energy budget, as reduced carbon assimilation will also result in changes in the surface albedo (due to less green plant material) and in the portioning of net radiation between sensible and latent heat fluxes. Since vegetation is geographically heterogeneous, the role of the ozone in altering regional patterns of diabatic heating may be at least as large as its effect on the global average radiative forcing effect due to altering the atmospheric concentrations of CO2!

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A Summary Of “Causes Of Land-use And Land-cover Change By Eric Lambin and Helmut J. Geist

A summary article by Eric Lambin and Helmut J. Geist entitled “Causes of land-use and land-cover change” succinctly summarizes the reasons for land-use and land-cover change [thanks to Jason English for alerting us to this!].

The Introduction reads,

“Identifying the causes of land-use change requires understanding both how people make land-use decisions (decision-making processes) and how specific environmental and social factors interact to influence these decisions (decision-making context). It is also critical to understand that land use decisions are made and influenced by environmental and social factors across a wide range of spatial scales, from household level decisions that influence local land use practices, to policies and economic forces that can alter land use regionally and even globally.”

They do not discuss the role of these changes within the climate system, however, their article provides an excellent summary of how humans are altering this climate forcing.

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New Paper On The Role Of Landscape Degradation And Resultant Dust On The Climate System

There is an interesting paper on the role of dust within the climate system that may also be relevant for the record loss of Arctic sea ice in recent years. It is

Painter T. H., A. P. Barrett, C. C. Landry, J. C. Neff, M. P. Cassidy, C. R. Lawrence, K. E. McBride, G. L. Farmer (2007), Impact of disturbed desert soils on duration of mountain snow cover, Geophys. Res. Lett., 34, L12502, doi:10.1029/2007GL030284.

The abstract is

“Snow cover duration in a seasonally snow covered mountain range (San Juan Mountains, USA) was found to be shortened by 18 to 35 days during ablation through surface shortwave radiative forcing by deposition of disturbed desert dust. Frequency of dust deposition and radiative forcing doubled when the Colorado Plateau, the dust source region, experienced intense drought (8 events and 39–59 Watts per square meter in 2006) versus a year with near normal precipitation (4 events and 17–34 Watts per square meter in 2005). It is likely that the current duration of snow cover and surface radiation budget represent a dramatic change from those before the widespread soil disturbance of the western US in the late 1800s that resulted in enhanced dust emission. Moreover, the projected increases in drought intensity and frequency and associated increases in dust emission from the desert southwest US may further reduce snow cover duration.”

The discussion includes the text,

” Expansion and intensification of grazing, recreational use and agriculture over the past ~140 years has increased the dust emission from the Colorado Plateau and other desert regions of the western US [Belnap and Gillette, 1997; Neff et al., 2005; Reynolds et al., 2001]. Therefore it is likely that the above changes in snow cover duration and surface radiative forcing increased significantly with human activity in the late-1800s, as desert surface crusts were disturbed and dust was more freely emitted to the Rocky Mountains and other mountain ranges of the western US that are downwind of disturbed soils. Analyses similar to those performed for the San Juan Mountains and an analysis of time series of dust deposition from mountain lake sediments across the western US will provide a clearer understanding of the spatial and temporal extent of this shortening of snow cover duration.

The phenomenon of increasing dust emission exists beyond the western US and is global in nature with the potential to continue to perturb resource-critical mountain snowmelt systems. Dust emission frequency in China from the Taklimakan and Gobi deserts (proximal to the Tien Shan and Altai ranges) has increased from one event in ~35 years for the period AD85-1949 to annual since 1990 [Liu and Diamond, 2005]. A four-fold increase in dust deposition over the previous two centuries was found in the Dasuopu glacier ice core at elevation 7200 m in Tibet [Thompson et al., 2000], with the continuum increase attributed to increased land usage whereas the interannual variability attributed to interannual changes in precipitation. The drying of the Aral Sea has affected enormous increases in dust emission that frequently deposits in the Tien Shan, Pamir, Himalaya, and Altai Mountains [Waltham and Sholji, 2001]. Dust deposition to the Antarctic Peninsula has doubled in the 20th Century due to the coupled effects of changing climate and land degradation”

The article continues with assuming that droughts will become worse with “global warming”, which, as Climate Science has discussed (e.g. see), has not been shown to be a robust prediction. Nonetheless, the paper does show that even without “global warming” the human intervention in landscape management (deliberate and inadvertent) has major consequences in altering the climate system on the global scale.

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Climate Science Is Retiring – Thank You To Everyone For Your Participation!

I want to thank everyone who has contributed to the diverse subjects on Climate Science! The site has been active since July 2005. However, the maintenance and preparation for the weblog requires quite a bit of time, and I have decided to move onto other activities. I have also extensively presented my perspective on climate science. The weblog will remain available as an archive on our research website.

After the remaining weblogs have posted (on September 2), the last weblog will identify where the archive can be found. Comments, of course, will not be accepted after that time, but the entire history of the weblog will be available for those who are interested.

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Further Analysis Of Radiative Forcing By Norm Woods

In the book

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

we presented results by Norm Woods (who works with Graeme Stephens) on the magnitude of radiative forcing for three types of vertical temperature and moisture soundings (tropical; winter subarctic and summer subarctic). Climate Science has summarized this study in the past (e.g., see the May 5th blog entitled Relative Roles of CO2 and Water Vapor in Radiative Forcing).

This weblog presents further analyses of these soundings by Norm Woods.

The total forcings are evaluated as the increase in flux convergence at the tropopause, and also divided these into the atmospheric and surface portions. As before, these results are for a change from 280 to 560 ppmv of CO2 [Norm presented this values with the same precision as the model output to show that they balanced].

Among the interesting results that he found is that the subarctic winter has the weakest total forcing, but the greatest surface forcing.

These results illustrate why presenting a single number of radiative forcing as a metric of climate change (such as given in Figure SPM.2 in the 2007 WG1 Statement for Policymakers of the IPCC) is a poor way to assess how the radiative forcing of CO2 and water vapor actually affect weather and other aspects of the climate system. Both the regional and vertical forcing vary geographically and with season, and obviously a global average top of the atmosphere radiative forcing does not capture this important heterogeneity in the climate forcings (also see).

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Final Agenda posted for NSF Workshop starting Monday August 27th

The final agenda is now posted for the NSF sponsored workshop on Detecting the Atmospheric Response to the Changing Face of the Earth: A Focus on Human-Caused Regional Climate Forcings, Land-Cover/Land-Use Change, and Data Monitoring starting Monday August 27th in Boulder, Colorado. Late registrations will be taken at the registration desk starting at 7:45 am on Monday. If you have any questions or would like more information, please contact Dallas Staley at dallas[at]cires.colorado.edu

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Part 2: Feedbacks, the Infrared Iris, and the Role of Precipitation Processes by Roy Spencer

Feedbacks and the Importance of Short Time Scales

In my last post, I used a simple time-dependent energy balance model to demonstrate that our traditional methods of shortwave feedback diagnosis from observational data are likely leading to “false positivesâ€?. Without going into great detail again, suffice it to say that much of the interannual SW variability we see in the tropics is likely to be the result of non-feedback cloud forcing. This will always act to bias any diagnosed feedback (even a negative one) in the positive direction, which would then mislead climate researchers in their development and validation of cloud parameterizations and estimates of climate sensitivity.

The example I showed in that post used simple daily random variations in low cloud coverage, which produced substantial interannual (and even decadal) time scale SST behavior in the model’s swamp ocean. A typical positive feedback value of -1.4 W m-2 K-1 was diagnosed from the cloud-forced SST variability (based upon 365 day averages), even though no cloud feedback was specified. We are currently working on a new paper describing the results of this investigation.

As was advocated by Aires and Rossow (2003 QJRMS), as well as Stephens (2005 J. Climate), our results suggest the importance of examining short time-scale behavior if we are to have any hope of observationally diagnosing cloud feedbacks. Once the data are averaged to seasonal or annual time scales, there is little hope of determining how much of the signal being analyzed is cloud forcing versus cloud feedback (cause versus effect).

But if we are to perform analyses on short time scales, a new issue arises: Is surface temperature necessarily the best reference for identifying cloud feedbacks in the observational data when short time scale behavior is analyzed?

Surface Temperature or Tropospheric Temperature?

Stephens (2005) pointed out that there is no rigorous justification for choosing surface temperature as a reference when doing feedback analysis. I believe that surface temperature is probably a logical choice when addressing the long-term equilibration to a new climate state (say from the radiative forcing due to increasing CO2) since both the surface and troposphere are expected to warm by roughly the same amount. Really, either one could be used as a temperature reference in this case.

But when we analyze the real climate system on interannual time scales, the signals we see do not represent long-term re-equilibration between two climate states. Instead, we are probably seeing relatively high frequency behavior that represents different states of disequilibrium in the system.

I will argue that, in the case of non-equilibrium short term variability, it is better to examine tropospheric temperature as a reference, rather than surface temperature. And here’s why. When we look for a cloud feedback signature in observational data, we are implicitly asking, “How do clouds respond when the surface warms?â€? Well, given that most cloud activity is going to be caused by convective transport processes of one kind or another, we can expect that a surface temperature peak will precede the atmospheric response. In the case of our GRL analysis of the composite ISO, the time scale of this ocean cooling/tropospheric warming was one to two weeks.

Thus, on short time scales, the cloud response is probably more related to how the tropospheric environment has been modified as a result of convective heat transport, rather than to the surface temperature at that time. In other words, by the time the troposphere has been modified and the resulting cloud feedback appears, the surface has already been cooled to provide for that vertical heat transport! Any cloud feedback would then likely occur in proportion to the time rate of change of SST, but in direct proportion to tropospheric temperature.

The Infrared Iris Effect

Ever since John Christy and I started doing the global temperature monitoring with MSU back in 1989, I had been intrigued by the large intraseasonal oscillations (ISOs) we saw in tropospheric temperature. I have always believed that there were secrets to the fundamental operation of the climate system contained in those fluctuations. So about a year ago, I finally decided to investigate them.

In our resulting August 9 GRL paper we did not use surface temperature to reference the daily variations to, but instead tropospheric temperatures, which in the tropics vary mostly in proportion to variations in latent heating (precipitation). The tropical average surface signal of the intraseasonal oscillations was very small, while the tropospheric temperature variations were very large.

In something of a “fishing expeditionâ€? we examined a variety of satellite observations that could be related to the tropical tropospheric heat budget. For the 15 largest intraseasonal oscillations between 2000 and 2005, we averaged TRMM TMI rainfall and SST, Terra MODIS cloud fractions, CERES reflected SW and emitted LW fields, and AMSU-A tropospheric temperature data to daily time scales, over tropical average space scales. The result was clear evidence in support of Lindzen’s “Infrared Irisâ€? hypothesis, at least on the intraseasonal time scales we examined. (Unpublished was an analysis of the 15 next-largest ISOs, which revealed very similar signatures.)

We demonstrated though that composite analysis of 15 ISOs that enhanced rainfall activity and warming of the tropical troposphere leads to enhanced loss of LW radiation to space in the cloudy areas, as measured by the CERES instrument on Terra (see figure below). When the LW flux anomaly was normalized by the latent heat release anomaly (panel D), a linear increase in LW loss with time is seen during the period of above-average rainfall. This change is dominated by the cloudy areas (compare “all-skyâ€? to “clear skyâ€?).
spencer-pielke-blog-figures-1.png
This CERES-observed change in LW flux was supported by ice cloud measurements from the MODIS instrument on Terra, which showed that the LW increase coincided with decreased ice cloud fraction (see second figure; panel C is cloud top temperature). We had additional, but unpublished, evidence that it was a decrease in thunderstorm anvil clouds that was primarily involved.
spencer-pielke-blog-figures-2.png
Interestingly, when the SW and LW anomalies were summed together for the composite ISO, the net radiative cooling of the ocean-atmosphere system was in direct proportion to tropospheric temperature, supporting the use of tropospheric temperature as a reference for feedback analysis. Interpreted as a feedback parameter, the enhanced cooling rate was a comparatively large 6 W m-s K-1.

It is of some interest what the previous critiques of Lindzen’s original Iris work did not see the effect that we measured. While I am only speculating at this point, I suspect the answer is related to some combination of two effects: (1) Those critiques dealt with a restricted region: Lindzen’s original paper used one-ninth of the longitudinal extent of the tropics; and (2) the variations were related to SST, rather than tropospheric temperature, and so there was likely a significant time lag in the resulting relationships.

The Connection to Long-Term Climate Sensitivity

The critical question is this: What, if anything, do these observations have to do with long-term climate feedbacks and climate sensitivity? Well, when it comes to convection and clouds, all we have is short term behavior to analyze. And as discussed above, if we average to seasonal or annual time scales, we have largely averaged out the relationships that might have indicated to what extent feedbacks, versus non-feedback cloud forcing, were involved.

So, while these new satellite observations do not prove negative cloud feedback in the context of long-term forcing, neither do current “feedbackâ€? interpretations based upon observed interannual variations in the climate system. Recall the three other pieces of evidence from my previous posting, the first two of which were based upon the energy balance model calculations: (1) the CERES-observed monthly variability in reflected SW radiation is much too large to be explained in terms of feedback…they must be dominated by non-feedback cloud forcing, and any underlying feedback signal is likely being obscured; (2) the low correlation in the resulting relationship between SST and SW also suggests a forcing interpretation, since a feedback relationship should have a very high correlation; and (3) in the case where Pinatubo (rather than cloud forcing) was the dominant source of interannual SST variability, the SW feedback signal was less “maskedâ€?, and the resulting diagnosed SW “feedbackâ€? was, in fact, negative.

For these reasons, I believe that the current satellite results are more likely to be related long-term climate sensitivity than are current (mis)interpretations of “feedbackâ€? from natural, internal variability in the climate system.

The Fundamental Role of Precipitation Processes

I am increasingly convinced that the primary atmospheric control over climate sensitivity is the precipitation process. Our new satellite measurements showing a change in ice cloud (anvil cloud, really) during the period of enhanced tropical rainfall suggests a change in microphysical processes in clouds.

Since any condensate that does not precipitate out must, by definition, be detrained back into the environment as cloud and vapor, precipitation efficiency must somehow be involved in the observed changes. This issue is not just restricted to the tropics, since the same concept applies to precipitation systems everywhere. For instance, the extreme aridity of cold polar air masses in the winter, as well as of the air sinking over the Sahara desert, can be traced to precipitation processes somewhere else. It will be important to repeat our satellite analysis for the extratropical regions.

I believe that precipitation systems act as a thermostatic control mechanism on the climate system. Even though relatively small in their spatial extent, tropospheric air is continuously being recycled through them, and most of the Earth’s natural greenhouse effect is, directly or indirectly, controlled by them. Remember, the control is not just through detrained moisture, but also through the moist convective controls over tropospheric temperature lapse rates everywhere, which in turn affect cloud formation (e.g., marine stratus clouds).

The sensitivity of our climate to precipitation microphysical processes is not a new issue, as it has been previously demonstrated in the modeling studies of Grabowski (2000 J. Climate) and Renno et al. (1994 JGR), and was implicit in Lindzen’s original 1990 BAMS article on potential negative feedbacks in the climate system. But it has been largely ignored. To the extent that any of these microphysical processes have a temperature dependence, climate feedbacks can be expected to result.

I predict that, as we learn more about the temperature dependence of precipitation processes and their resulting control over precipitation efficiency, estimates of climate sensitivity will decline. But at this point, there is too little awareness of this issue in the climate community, and it will take time before a critical mass of climate modelers and diagnosticians forms and starts to take the issue seriously.

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The Bunny Fence Experiment In Western Australia – A Field Campaign To Better Understand The Role of Landscape As A Climate Forcing

There is an ongoing study of land use change, led my my close research colleague, Udaysankar Nair, that will add to our understanding of the role of landscape in weather and climate. The program is called BUFEX for The Bunny Fence Experiment. The New York Times published an article on this program by Sonal Noticewala on August 14 2007 entitled “At Australia’s Bunny Fence, Variable Cloudiness Prompts Climate Study“.

A University of Alabama at Huntsville press release summarizes this field campaign to collect real world data on this climate forcing. The July 31 2007 news article reads,

“What is happening along the bunny fence to keep rain off SW Australia’s farmland?

Something odd is happening to the weather along hundreds of miles of bunny fence in Southwestern Australia.

Two scientists from The University of Alabama in Huntsville are part of an international team that will spend August studying why most of the clouds that form in that region form over the native vegetation north and east of the fence line, instead of the farmland on the other side of the fence.

Even rain seems to keep on the bunny side: Rainfall over the farm area might have fallen as much as 20 percent since it was cleared for agriculture.

“There are multiple things going on, so we haven’t proven that the changes in clouds and rain are due to clearing native vegetation,” said Dr. Udaysankar Nair, a research scientist in UA Huntsville’s Earth System Science Center and one of the study team’s leaders.

The leading theory is that the dark-colored native plants absorb more sunlight and release more heat into the atmosphere than the lighter-colored farmland. The rising heat may carry both energy and water vapor into the upper atmosphere, where they can combine to form clouds.*

There is some evidence to support that theory: Satellite and aircraft observations often show clouds forming over the native vegetation and abruptly ending at the fence, especially during the spring and summer.

‘Even when the fields are covered with crops on one side, it isn’t as dark,’ Nair said. “There isn’t enough thermal ‘kick’ to form clouds.”

This year’s research expedition is the third studying the impact of changing land use on cloud formation, rain and wind, with prior studies in December of 2005 and 2006 that looked at summer conditions after the harvest. This year the team will focus on the winter season while crops are growing. With funding from the National Science Foundation and the Australian Research Council, scientists from the U.S., Australia and Germany will use instruments on the ground and carried aloft by airplanes and balloons.

The data they gather is plugged into computer models of the atmosphere to help determine why the weather is changing in that region.

While the energy budget difference between the two sides of the fence will be studied, other factors related to land use might also be influencing cloud cover and rain, said Nair, including changes in local circulation patterns and how many small particles are being lifted from the surface into the atmosphere.

Differences in temperatures over the native scrubland and the farm region might also be changing wind patterns, with warm convective upwelling over the hot, dry scrub pulling cooler, somewhat damper air in from across the fence – what the team refers to as the ‘corn breeze.’

These temperature differences might also be altering the local sea breeze. The study’s early data shows the daily sea breeze arriving over the warmer native vegetation side of the fence earlier than over the cooler farm side.

When the team looked at clouds over the region, they found physical differences between clouds over the farm region and clouds over the native scrubland. These changes might be due to differences in the size of water droplets inside the clouds.

‘The size of the cloud droplets depends on aerosols ‹ the particles of dust, soot and salt suspended in the atmosphere,’ Nair said. ‘Aerosols have an important role in forming the nuclei for water vapor to attach to, forming droplets and clouds. But there is a trip point. If you have small aerosol particles or too many particles the chance of rain goes down.’

‘Because of that, cloud cover doesn’t always translate into more rain. With fewer aerosols you might get fewer clouds but more rain.’

‘When we made a small sample of aerosol measurements, we found that on the agriculture side there were more aerosols and more fine aerosols. Our initial results indicate the possibility that there are so many particles and so small that they form a lot of small droplets, which are less conducive to rain.’

The team found that during late spring and summer, dust devils ‹ heat-powered vortices that can stretch more than 50 meters high ‹ might be contributing to the aerosol differences by giving aerosol particles a boost into warm, rising air. While dust devils form on both sides of the fence, they are more likely to form on the farm side of the fence where there is less ground cover and the ground is ‘smoother.’

Other possible sources of fine aerosols are areas where salt is being leached into the soil by a rising water table, including new salt flats growing on the farm side of the fence. When farmers cleared 13 million hectares for cultivation, they cut down the deep-rooted native trees. The roots of these trees reached into and pulled water from the water table. When the trees were destroyed the water table began to rise, bringing dissolved salts to the surface.

Not only do the salts destroy crops, they are also a ready source of fine grain aerosols.

‘Since these salts are being brought to the surface as a byproduct of land use change,’ Nair said, ‘increased aerosol production coupled with more efficient dust devil formation over the agricultural area shows one of the complex ways land use change might influence the atmosphere.’

‘This is the opposite of what we experience in the Southeastern U.S., where forests transpire water that cools the air above them. Plants that evolved in the dry Australian climate, such as eucalyptus trees, release very little of their precious water into the air. Much of the soil in Southwestern Australia is sandy and bright, so without vegetation for cover it is bright and reflective. This reflective soil reflects sunlight back into space rather than absorbing it and converting it to infrared heat.”

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