Drought regions by 2099……Credit: National Center for Atmospheric Research (USA)
According to Aiguo Dai, lead climatologist for a new study released by the National Center for Atmospheric Research (NCAR) [Drought under global warming: a review] the signs of increasing drought are already visible. They will become obvious and severe by 2030. By 2099 some areas of the globe will experience drought that exceeds known historical experience. The study puts figures and maps to the predictions. Within a decade or two the projections should be measurable, literally, as in rainfall – or its lack – to document the effect of climate change.
“We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community,” Dai says. “If the projections in this study come even close to being realized, the consequences for society worldwide will be enormous.”
Previous work by Dai and other climatologists indicate that the percentage of Earth’s land suffering persistent droughts more than doubled between 1970 and 2000. The new study was developed using data and results from 22 computer models used for the 2007 IPCC global climate change report and fed into a new model that uses the Palmer Drought Severity Index (PDSI) as a measuring tool. On this scale +0.5 to -0.5 is normal, -4 is extreme drought, -6 is exceedingly rare.
By the 2030’s the new projections indicate that, for example, some areas of the United States Rocky Mountain West may experience droughts ranging from -4 to -6 on the Palmer scale, and parts of the Mediterranean may see droughts at -8. The projections get much worse: by 2099 some areas of the central and western United States could see readings in the range of -8 to -10, and the Mediterranean -15 to -20.
These projections are tied to historical records of temperature, precipitation, humidity, wind speed, and Earth’s radiant balance (how much sunlight is absorbed by the Earth). The model also includes estimates for the effect of global warming due to greenhouse gases. So, yes, this is a global warming model. It makes predictions that can be verified by actual measurements in the coming years. Of course, if the model is correct, by 2030 the effects of increasing drought should be obvious. In particular, many areas most affected by more frequent and severe droughts are heavily populated. Shortages of fresh water for agriculture and industry are already occurring in many of these areas. Increasing drought will have unmistakable economic, social, and political impact.
Dai and other atmospheric scientists caution that while the predictions are regional in nature, they are affected by global weather patterns such as el Nino that from year to year change regional weather dramatically. As ever with climatology, trends measured over years and decades are significant. Local and short term variations are expected. For example, most models indicate that the many northerly regions – Scandinavia, Alaska, Russia, Canada – will become wetter.