Climate Change in Our World

Climate Photo of the Week

Abnormal dryness to severe drought conditions grip 80 percent of the lower 48 States .

Update to this post, 18 July 2012:

More than 80 percent of the area of the lower 48 states is in drought and dry conditions, and by one measure the lack of normal moisture covers the most area since the deep droughts of the 1950s. The National Drought Monitor map and analysis as of July 3, by the National Drought Mitigation Center, shows areas suffering "exceptional drought" to "abnormally dry" conditions in every state except Maine. Areas of "extreme" and "exceptional" drought range from the Four Corners in the Southwest and across most of Colorado, New Mexico and Kansas, in the Ohio and Mississippi River valley, and across Georgia and adjoining southern states. The area affected by drought and abnormal dryness is more than double what it was in the blazing summer of 2011. The monthly-calculated Palmer Drought Index for June also showed more than half the nation in persistent drought, the most since 1956.

The yearly "State of the Climate" report for 2011 from NOAA and the American Meteorological Society, released July 10, shows that across the globe 2011 was cooler than 2010 because of persistent La Nina conditions, but was still in the top 15 warmest years of the 124-year measured record. But of course 2011 was the year of many extreme weather events, such as the Texas/Okahoma drought, droughts in Africa, deadly floods in Thailand and extreme heat, cold, and precipitation in Europe. A study released with the State of the Climate report, "Explaining Extreme Events from a Climate Perspective," used new analysis techniques to find that five of the six events studied, including the Texas drought, were more likely to have happened because of global warming. Scientists who were part of the study, as well as other researchers, cautioned that they are just learning how to interpret extreme events within the changing atmosphere and continuation of normal cycles like La Nina/El Nina. Overall, though, the report said:
"The accumulating body of evidence on the human contribution to changes in temperature extremes is robust, and leads to the assessment that 'it is likely that anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures on the global scale' .... Heavy precipitation has been found to contribute an increasing fraction of total precipitation over many of the regions for which good instrumental records are available, indicating an intensification of precipitation extremes."

Also see an article about this report in the NY Times.

Over the past century heat waves and droughts were the greatest cause of death from weather events in the US. More than 15,000 people were killed in the 1980 and 1988 droughts. Until Hurricane Katrina, droughts were also the most expensive disasters. Current dryness does not yet compare with the widespread severity of droughts in the 1930s, 1950s and 1980s. Furthermore, droughts in North American pre-history were much worse: Research by scientists at Lamont Doherty Earth Observatory revealed "unprecedented megadroughts over the past millennium that clearly exceed any found in the instrumental records." North American droughts appear tied to Pacific Ocean temperatures and the ENSO cycle, which are affected by and can accentuate climate change effects. Current trends show more droughts and heatwaves are occurring worldwide.

The drought today is both a symptom of climate-driven moisture changes and a contributing cause of record elevated temperatures and wildfire. In these combined events we are seeing the kinds of effects of climate change which have long been predicted by accepted atmospheric science. Speaking on NPR on July 4, Dr. Kevin Trenberth of the climate analysis section of the National Center for Atmospheric Research, said these are the "consequences of the climate change influence that has exacerbated the drought and the heat waves." Speaking of the record high temperatures, Trenberth said, "You know, as time goes on, we always expect to set new records, but there should be an equal number of highs and lows. And in the 1950s and the '60s and '70s, that was the case. But by the time we got to the 2000s, the ratios of highs to lows was about two-to-one and this year so far it's running at about a ratio of ten-to-one. And so clearly this is just not natural variability anymore."

Thanks to scientists Richard Seager, Brad Rippey, Rich Tinker and Richard Heim for drought information.

For more analysis of the climate change effects seen in fires, heat and drought, see articles by Climate Central, Climate Communications and the New York Times.

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