November 14, 2006

Darn Drought Data

Filed under: Droughts, Precipitation

We have all heard the news that droughts will certainly become longer, more frequent, and more severe thanks to global warming. Higher temperatures will surely increase rates of potential evapotranspiration, and even if precipitation patterns remain unchanged, the odds will favor more droughts in the future. The Intergovernmental Panel on Climate Change (IPCC) states in the 2001 Summary for Policymakers that it is “Likely” that “Increased summer continental drying and associate risk of drought” has occurred in the later half of the 20th century and “Likely, over most mid-latitude continental interiors” to occur during the 21st century.

Figure 1 below shows the current state of affairs as of November 4, 2006, and generally, widespread drought in the mid-latitude continental interior is absent. In fact, as we look at the Great Plains, we find more areas in the “Extremely Moist” category than the “Extreme Drought” category. We would all agree that one snapshot of soil moisture conditions in the United States is not an adequate way to test the idea that global warming will lead to an increase in drought in mid-latitude continental interiors. What is needed, of course, is a longer perspective with drought information over hundreds of years.


October 19, 2006

Bogged Down in Soil Moisture

Filed under: Droughts, Precipitation

The Intergovernmental Panel of Climate Change (IPCC) provides itself a great deal of wiggle room in its predictions of future soil moisture levels. On one hand, IPCC predicts in the future that “The globally averaged mean water vapour, evaporation and precipitation increase.” That makes sense when one considers that warmer temperatures will cause an increase in evaporation, and the water that evaporates will ultimately fall from the sky. IPCC also predicts “Most tropical areas have increased mean precipitation, most of the sub-tropical areas have decreased mean precipitation, and in the high latitudes the mean precipitation increases.” Of course, IPCC predicts (and Gore et al. make the most of it) “Intensity of rainfall events increases.” But with respect to the United States, IPCC predicts “There is a general drying of the mid-continental areas during summer (decrease in soil moisture). This is ascribed to a combination of increased temperature and potential evapotranspiration that is not balanced by increases in precipitation.”

Yet another article has appeared in the literature that provides effectively zero empirical support for the prediction of decreased summer soil moisture levels. The latest article is entitled “Summer moisture availability across North America” and is published in the Journal of Geophysical Research by a team of scientists from the United States and United Kingdom. The van der Schrier et al. group reviewed the literature on drought studies in the United States and correctly identified that (a) many researchers use the very popular Palmer Drought Severity Index (PDSI) and (b) the PDSI has many substantial limitations. Among its many problems, they note “A significant drawback of the PDSI is that despite its intended value as a geographically comparable index, it can be poorly suited for investigation of moisture conditions across diverse climatological regions.”


October 13, 2006

Where are the Droughts?

Filed under: Droughts, Precipitation

One of the pillars of the greenhouse apocalypse is the global warming will lead to a higher frequency, intensity, duration, and spatial extent of droughts in the future. This prediction is fairly easy to understand in terms of basic physical principles. Higher temperatures will lead to higher rates of potential evapotranspiration (PE), so even if rainfall stays the same or even increases slightly, the increase in PE will make droughts worse, make them last longer, make them more frequent, and make them expand their spatial extent. To make the matter even scarier, many climate models predict a decrease in precipitation in continental interiors, so with less rainfall, higher temperatures, and higher PE rates, drought frequency, intensity, spatial extent, and duration may substantially increase in places like the American heartland.

Literally dozens of articles have appeared in the scientific literature showing results that lead to the prediction of increased drought conditions in the central United States. The Intergovernmental Panel of Climate Change (IPCC) states in the Summary for Policymakers that “Increased summer continental drying and associated risk of drought” is “Likely, over most mid-latitude continental interiors” during the 21st century. In terms of seeing such a pattern in the observed climate record in the 20th century, the IPCC concludes it is “Likely, in a few areas.”

An important article appeared in the literature recently with some surprising results given the predictions of the climate models. Konstantinos Andreadis and Dennis Lettenmaier of the University of Washington have published a paper in Geophysical Research Letters entitled “Trends in 20th century drought over the continental United States,” and the results are peculiar—in light of climate model projections—to say the least. In the abstract, they write “Droughts have, for the most part, become shorter, less frequent, and cover a small portion of the country over the last century.”


July 7, 2006

The Fire This Time: More Perspective Needed

Filed under: Droughts

Some prominent scientists are becoming increasingly restive about the shrill portrayal of global warming science in popular media. The latest round concerned a paper by A. L. Westerling (Scripps Institute of Oceanography) relating an dramatic increase in western forest fires to regional warming and changes in the onset of snowmelt.

Coloroado University’s Roger Pielke Jr., one of the nation’s preeminent scholars about how science and society interact, called it “a useful paper that adds to our knowledge and hopefully will stimulate further research on the integrated effects of climate-society-policy.” But then, he warned that “At the same time I can envisage the paper being used simply as a caricature in the global warming debate—Global Warming Causes Forest Fires!—but that would be a shame because fire policy is more complex than that.”

Well, of course, what he feared would happen, did happen. And the resultant headlines are another sad commentary on how cursory reporting on global warming has become, and how little attention is paid to the facts as they stand. Nowhere, for example, did we read Westerling’s words: “Whether the changes observed in western hydro-climate and wildfire are the result of greenhouse gas-induced global warming or only an unusual natural fluctuation, is presently unclear.”

Why so unclear? In large part, because the science isn’t straightforward, and three decades is a very short period of climate time.


April 8, 2005

Climate Perspectives: The Great Early 20th Century Rainy Period in the American West

One of the problems in communicating climate science concerns peoples’ perceptions versus climate reality. For example, most middle-to-slightly-older-agers who grew up in the Mid-Atlantic region will tell you that it just doesn’t snow like it did in their youth (and usually they will blame global warming). Indeed, the 1960s were a very snowy decade. But somehow, we tend to view what we grew up with as “normal,” while everything different in our adult lives is “abnormal.” [Caution: this applies to more than weather and climate.]

Consider what happened in the American West in the early 20th century, when population grew roughly 50% from decade-to-decade, the largest regional growth spurt in post-colonial American history. People were lured by warm temperatures and abundant moisture. For much of that period, believe it or not, the West was a green paradise. Abundant moisture was so much du jour that allocation rights for Colorado River water, which have been contended ever since, were based upon what turns out to be the wettest period in nearly 1200 years. Had early 20th century planners had modern climatological analyses in their hands, it’s doubtful they would have been so profligate with water distribution from what really is the only big river in the Pacific Southwest.

February 7, 2005

No proof is sufficient

Filed under: Climate Models, Droughts

In the face of evidence resulting from their own research, some scientists refuse to abandon their preconceived idea: that computer-based climate models reliably forecast future climate.

We’ve come across research published in the peer-reviewed journal Geophysical Research Letters, the title of which pushes the limits of scientific acceptability: “Forty-five years of observed moisture in the Ukraine: No summer desiccation (yet).” It appears we have now entered a phase of the global climate change debate wherein scientists begin to trumpet their personal bias even if it runs contrary to evidence compiled by the scientific entity they represent or, even more astounding, if it runs counter to research results they themselves produce!

October 18, 2004

A Tale of Two Records

Research on the long-term drought history of the western United States doesn’t jibe with research on the long-term temperature reconstructions of the same region. When two records disagree, something is amiss.

May 12, 2004

Drought Doubt

Filed under: Droughts, Precipitation

The New York Times makes, but doesn’t test, a hypothesis that the drought in the western United States is related to human-caused global warming. Our tests prove it false.

Is the current five-year-long drought in the western United States linked to anthropogenic global warming? The masthead editorial in the May 10 New York Times leads its readers to believe that’s the case. Think of their supposition as a scientific hypothesis. One that you can test.

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