The Science Behind the U.S. Drought
Submitted by Kelly Levin on July 24, 2012
A farmer in the South plows a drought-parched field. Photo: Fonseca/CIMMYTThis post is part of WRI’s “Extreme Weather Watch” series, which explores the link between climate change and extreme events. Read our other posts in this series.
Heat and drought continue to blanket the United States, leaving 54 percent of the nation’s pasture and rangeland, 38 percent of its corn crop, and 30 percent of soybeans in “poor” or “very poor” condition. As of the end of June, 55 percent of the contiguous U.S. was experiencing moderate or extreme drought – the most extensive drought in more than half a century (see map from last week’s US Drought Monitor).
What’s Causing the Drought?
What we know is that recent temperature and precipitation levels have strayed significantly from historical averages (with, for example, 2012 being the warmest spring ever experienced in the U.S. since record keeping began in 1895). From the Southwest to the Great Lakes, temperatures have been so high and rainfall so low that the drying effect of warmer air temperatures far exceeded what little precipitation there’s been, resulting in moisture being drawn out of soils. This situation has occurred at a critical time in the country’s growing season, leaving the ground sapped of moisture and, in turn, wreaking havoc on crops and livestock. According to the National Oceanic and Atmospheric Administration (NOAA), even if a normal amount of rainfall occurred this year, it could not have offset the drying effect of the record-breaking heat.
In addition, recent warming across a large swath of the nation led to faster melting of already-reduced snowpack, which supplies water bodies as it melts. This has resulted in below average spring and early summer runoff and depleted reservoirs. For example, this year’s water flow to Lake Powell, which straddles the border between Arizona and Utah, is projected to be less than 50 percent of the average flow.
Credit: U.S. Drought MonitorIs There a Climate Change Connection?
So what explains these patterns? One factor could be La Niña conditions, which leads to shifts in weather patterns and can contribute significantly to drought in the Southwest. But it’s also important to note, as our colleagues at Climate Central explain, that these dry, hot conditions are occurring against a backdrop of human-induced climate change. Research shows that global warming intensifies both drought and heat, making drought even dryer and heat waves even warmer than they otherwise would have been without excess greenhouse gases in the atmosphere.
What Does the Research Say About Climate Change’s Future Impacts?
According to the U.S. Global Change Research Program (USGCRP), we will see more severe and frequent drought events in the U.S. if human-induced climate change continues unabated. This drought will coincide with rising temperatures, further straining water availability.
Declines in precipitation and increases in summer temperatures are projected for the Southwest in particular. This combination of effects will lead to “a serious water supply challenge in the decades and centuries ahead,” according to the USGCRP. Research indicates that the Great Plains, the nation’s breadbasket, with agriculture covering 70% of the region, will also witness rising temperatures and evaporation rates, as well as more sustained drought. Optimal growing zones will likely shift, affecting farmers, and pests are likely to come earlier given milder winters, resulting in greater numbers of insects.
What Do We Make of This?
Climate science is advancing in its ability to attribute individual extreme events to climate change. For example, a new NOAA report analyzed recent extreme events’ connections to climate change and found that the conditions leading to the 2011 Texas drought are 20 times more likely to occur now than in the 1960s due to increases in greenhouse gas concentrations and the resulting climatic changes. And it’s likely we’ll soon learn even more; the recent heat waves and drought will undoubtedly be the focus of intense scientific study in the coming years.
But we don’t need to wait for more scientific literature to know that the conditions we’re currently experiencing match projections of a warmer world. As U.S. politicians swelter while addressing the losses this drought is bringing to our economy, it’s time they also adopt a policy agenda that will reverse our carbon-intensive ways. Otherwise, this current drought will just be a taste of what’s to come – and come more often.
6 Comments
Regarding the NOAA report, I
Regarding the NOAA report, I have not looked through it yet, however it would be interesting to know how exactly they can to the conclusion that it is 20X as likely now for the same drought conditions in Texas. Texas had a rough year last year, and this year it looks like Colorado is being the hardest hit due to the droughts.
http://www.cityalice.com
I have "looked it up" and I
I have "looked it up" and I agree with 99% of the world's scientists and every national scientific organization on earth. Global warming is a reality and is due mostly, if not entirely, to anthropogenic causes.
The fact that the Earth has
The fact that the Earth has been warmer before does not mean that the current period of warming is not caused by humans, or that warming is not related to increased levels of greenhouse gases. That's not how cause and effect work. No one is saying that the sun has no impact on temperature.
That having been said, studies of ice cores, etc, indicate that periods of warming have corresponded with increased levels of CO2 in the atmosphere for thousands of years. While correlation does not equal causation, it remains a valid hypothesis, and so far all of the alternatives have actually failed to present a better explanation. Most studies examining the solar cycle hypothesis for recent warming have not been able to match the results of studies hypothesizing that the change is caused by increased CO2 levels.
There's no point in doing your own research if you cherry-pick the results in order to avoid bad news. That you think climate science is entirely predicated on data "gleaned from a 50 year time span" pretty much proves that you are not really paying attention.
The issue is not that the Earth is entering a warming period, but that it is warming much, much faster than it has before, because of additional factors that were not present before the industrial revolution. The concern is that species cannot diversify fast enough, and that humans will not be able to adapt quickly enough, to forestall disaster.
At the risk of sounding alarmist, think about what happened to the dinosaurs - a massive extinction event brought about by very rapid climate change. Rapid climate change won't eliminate life as we know it, but humans have a considerable stake in preventing it from happening.
Ignore the shills: Sunspot
Ignore the shills:
Sunspot activity has been decreasing since about 1975, but global Earth temperatures have been increasing steadily.
http://www.skepticalscience.com/solar-activity-sunspots-global-warming-i...
Models are not any more based on "assumptions" than your perception of reality. Scientific climate models can predict past temperatures accurately.
Dear Sirs: Thanks for your
Dear Sirs:
Thanks for your efforts and for the drought info. However, it is certain that the computer models you allude to and that you seem to think are revealing information about the cause of global warming and the cause of droughts are not at all meaningful. The computer "models" are generated based on assumptions. There are so many "correlation coefficients" put into them dealing with such minor changes in the data, that the builder of the computer model has to change his initial correlation coefficients so many times and to such large degrees, that all he is doing is forcing his model to tell him what he already "knows" that he wants it to tell him.
Lewis Bishop
There have been numerous
There have been numerous studies done by various agencies, including one funded by NASA 12 years ago, stating that climate change is more tied to solar activity - coronal holes, sunspots, and flares - than man-made global warming. These studies are out there. We can continue to believe this fallacy or we can accept there are things beyond our control. Temperatures began warming following the Carrington Event. It is also theorized that 300 years ago, a quadrupolar sun induced the Little Ice Age. Honestly, to assume the solar cycles do not influence the temperatures more is substantially ignorant. We are getting warmer because solar activity has been increasing. Once we hit solar minimum, temperatures will drop again. However, I am sure the cult of climate change followers will just say it was because we reduced CO2. I am sure, also, that many people will want links and empirical evidence. I just gave you the springboard. Google it. Don't bother arguing with me, I am not one of those who feels the need to argue. Milankovitch Cycles. Quadrupolar sun. Little Ice Age. Japan Hinode. If you really want to know, you will research it yourself without needing to be told 'the truth' like the rest of the sheep. The reason why you believe this: shoddy science, the fear of being wrong, and the Delphi method. Good luck! (P.S. I have spent a great deal of time studying historical geology and climate. Our earth has been warmer than this without AGW, and, in fact, species diversified during the warmest periods. We warmed considerably about 13000 years ago, immediately following an ice age - there have been a few - and since then, the 13000 year temperature scale shows a trend of cooling. Furthermore, to assume that the earth's optimum temperature can be gleaned from a 50 year time span, is a joke. Especially when considering the earth is 4.6 by. During the last 13000 years, the earth has experienced many periods of warm up. Then it cools down. Then it warms up. But the overall trend is down. If we are to assume that warming is caused by fossil fuels, then please explain the Paleocene-Eocene thermal maximum - which was the warmest time in the last 50 million years. Further more, the geologic record indicates that solar activity and sea-floor spreading cause more climate change. Last, there have also been times in the past - during one of the glacial periods - when CO2 levels far outweighed current levels. This in indicated in guide fossils and their ability to hold oxygen isotopes, such as belemnoids.) If we really want to help our climate we need to STOP cutting down trees, forests, and decimating plant life. Why? Plants REQUIRE CO2. Look it up. The truth shall set you free.
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