We have been told over and over that the buildup of greenhouse gases will vastly alter climate all over the world. The planet will be warmer, precipitation will be greater, droughts and floods will savage civilization, and everything will be worse than we could ever believe. In the case of the central United States, we have been warned repeatedly that higher atmospheric concentrations of greenhouse gases will lead to a substantial increase in the duration, severity, and areal extent of droughts in the American heartland.

A recent issue of Geophysical Research Letters includes two articles that shed light on the future (and past) of droughts in the central United States. The first article was produced by five climatologists from academic units at Purdue, Minnesota, Wisconsin, and Oregon. Diffenbaugh et al. focused on the Mid-Holocene period between 8,000 and 3,000 years ago — a period for which the proxy record clearly shows drier-than-present conditions throughout the central United States. They note that “Proxy data also indicate that changes in summer precipitation played a major role in shaping mid-Holocene moisture balance in North America.” Back then, summers were a lot drier than today, despite any lack of elevated concentration of greenhouse gases.

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Glacier National Park just seems to come up repeatedly in the debate about global warming. This poster child of the greenies is sacred ground, for it provides an opportunity to show the kids where the glaciers were when you were a kid, see where the glaciers terminate today, and of course blame global warming and further blame the Bush Administration for not signing the Kyoto Protocol. Many documentaries on the greenhouse effect have been drawn to the Park, and if you Google “Glacier National Park and Global Warming,” you will be directed to approximately 159,000 sites.

A very interesting paper on Glacier National Park appears in a recent issue of Earth Interactions by scientists at Montana State University and the U.S. Geological Survey. Pederson et al. begin their article noting that “Evidence from an increasingly rich paleoproxy record demonstrates that over the last millennium decadal to multidecadal precipitation anomalies have been a substantial, if not defining, component of western North America’s climates. As in the twentieth century, the last 1000 yr has experienced sporadic episodes of both persistent (>10 yr) droughts and wet regimes, though the magnitude and duration of many paleodroughts surpass those captured by the instrumental record.” The notion that droughts in the past were far worse than any recent drought brought our attention to the article, but there is far more to the story than just past droughts.

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A recent article in Geophysical Research Letters by Rutgers’ scientists Alan Robock and Haibin Li addresses the issue of global warming and reduced soil moisture levels in important agricultural areas. Every popular global warming presentation lays out the case that higher temperatures in the future will cause higher levels of evaporation that will overwhelm any changes in precipitation and force soil moisture levels to drop. Of course, crops will fail, we will have more frequent and severe droughts of longer duration, and it will have all been caused by elevated carbon dioxide (CO2) levels. You’ve heard the story a 1,000 times by now.

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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.

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Global climate models – the complex quantitative representations of Earth’s atmosphere and its interaction with the planet’s land masses and ocean bodies – have portrayed a future climate that is riddled with ferocious weather. Super hurricanes, more frequent and intense drought, flooding precipitation events, and unimaginable severe weather outbreaks lead the cast of villains that will supposedly be engineered by increased greenhouse gases in Earth’s atmosphere. An exaggerated image of a global climate gone mad is a wonderfully effective tool for climate change alarmists. Historically, severe weather has been an intrigue, as evidenced by the massive media coverage of events either in anticipation or in retrospection. Natural hazards can be viewed with guilt-free sympathy, as they are indeed natural and leave no one to blame. Incorporate weather extremes in the global warming debate and there exists an opportunity to indeed assign blame and make severe weather events less innocent. It’s the age-old strategy of making the public afraid of something before telling them who is to blame for it.

One form of extreme weather that gets little play by climate change alarmists is hazardous snowstorms. This is probably because the image of increased snow detracts from their portrait of a warmer climate. However, the increase in extreme weather predicted by global climate models “is anticipated to result in alterations of cyclone activity over the Northern Hemisphere” (Lawson, 2003), and that “a change in the frequency, locations, and/or intensity of extratropical cyclones in the mid-latitudes would alter the incidence of snowstorms” (Trenberth and Owen, 1999). In a recent article in the journal Natural Hazards, snowstorm data over the last half of the 20th century were analyzed in search of support for this theory.

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The Arctic region has become a bit of an epicenter of the global warming debate. Snow and ice cover are touted as effective monitors of large-scale climate change, the greatest warming in recent decades is said to have occurred over portions of the Arctic, and climate models predict that the region will experience some of the most significant warming in the future. Throw-in the idea that melting snow and ice increases the input of fresh water to the Arctic and northern Atlantic Oceans, which alters the oceanic thermohaline circulation, which changes the global climate further, and you can understand why the global warming crusade gets dreamy-eyed when thinking of the cold northern latitudes. The truth of the matter is that there have been many contradictions to the doomsday scenarios associated with the Arctic region – enough to champion a movie sequel “Day After Tomorrow 2: Hold the Phone!”

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Droughts and/or floods – blame global warming, right? Time and Newsweek are all too quick to blame either one on global warming, Al Gore’s movie certainly gave us vivid images of both severe droughts and severe floods, and to this day, ongoing drought in the Southwest is blamed on global warming in some circles. The Summary for Policymakers in most recent (2001) Intergovernmental Panel on Climate Change (IPCC) Report claims “In the mid- and high latitudes of the Northern Hemisphere over the latter half of the 20th century, it is likely that there has been a 2 to 4% increase in the frequency of heavy precipitation events.” Also, IPCC notes “Over the 20th century (1900 to 1995), there were relatively small increases in global land areas experiencing severe drought or severe wetness.” However, IPCC claims “In some regions, such as parts of Asia and Africa, the frequency and intensity of droughts have been observed to increase in recent decades.” In the main body of the document, we find in Southern Africa “significant decreases in precipitation being observed since the late 1970s.”

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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.”

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The depth and extent of Earth’s snow cover have been championed as tools for measuring climate variability and change since the early 1970s when satellite-derived measurements of large-scale snow became reliable. The scientific literature of recent years is well stocked with research articles that document various trends toward decreasing snow cover across portions of the Northern Hemisphere. This corresponds nicely with the atmospheric warming that has occurred across the hemisphere, and intuition leads to the conclusion that snow cover reduction is a response to global warming. Armed with this idea, it’s off to the global warming debate we go…on the wings of a common mistake. A deeper intuition suggests that precipitation is also a necessary ingredient of snow cover, and therefore variability in snow cover is not solely dependent on temperature.

One can argue that across Earth’s cryosphere, or its frozen realm, precipitation can be more completely monitored with snow cover than can atmospheric temperature. Consider this: decreases in snow cover across regions with seasons that are persistently below freezing have nothing to do with air temperature and they have everything to do with precipitation. This fact is well demonstrated in a recent article appearing in the Journal of Climate: “Snow cover distribution, variability, and response to climate change in western China” authored by Qin Dahe of the Cold and Arid Regions Environmental and Engineering Research Institute in Lanzhou, China, and two of his colleagues. The impetus for their work is twofold: (1) snow cover is a vital water resource in western China, and (2) “The majority of the climatic community is convinced of a pronounced reduction in seasonal snow cover in response to CO2-induced global warming.” In partial response to the second issue, Dahe et al. point out that “Up to now global snow cover monitoring has not found any convincing evidence of the trend in snow cover variations on global scale.”

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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.”

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