Prize winning UN IPCC Climate Report method overestimated drought by 7 times says Nature Magazine study

11/14/12, “Little change in global drought over the past 60 years,” Nature.com, Letter

• Justin Sheffield, Eric F. Wood & Michael L. Roderick

“The simplicity of the PDSI [Palmer Drought Severity Index], which is calculated from a simple water-balance model forced by monthly precipitation and temperature data, makes it an attractive tool in large-scale drought assessments, but may give biased results in the context of climate change⁶. Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation⁷ that responds only to changes in temperature and thus responds incorrectly to global warming in recent decades. More realistic calculations, based on the underlying physical principles⁸ that take into account changes in available energy, humidity and wind speed, suggest that there has been

• little change in drought over the past 60 years.

The results have implications for how we interpret the impact of global warming on the hydrological cycle and its extremes, and may help to explain why palaeoclimate drought reconstructions based on tree-ring data diverge from the PDSI-based drought record in recent years^{9, 10}.”

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IPCC report said results weren’t guaranteed accurate on this matter but most people ignored that warning.

11/15/12, “Scientists have found that the method used by the IPCC to measure droughts has significantly overestimated their number during the the past 60 years.” Robert Zimmerman, Behind the Black

“The uncertainty of science: Scientists have found that the method used by the IPCC to measure droughts has significantly overestimated their number during the the past 60 years.

Although previous studies have suggested that droughts have increased over that 60-year period, the team’s new analysis hints that the increase in drought has been substantially overestimated. For instance, the new assessment technique found that between 1980 and 2008, the global area stricken by drought grew by approximately 0.08% per year—less than one-seventh the increase estimated by the temperature-only [IPCC method].

The IPCC and the global warming activists that run it had claimed that the warming climate was causing more droughts. It turns out that claim was essentially false. The number of droughts has apparently not gone up. Note that this fact is actually not a surprise to those who have read the IPCC reports carefully. Deep down past their simplistic summaries, the reports have consistently pointed out that these conclusions were very uncertain and could be found to be wrong.
Not surprisingly, the article above spends a lot of time trying to rationalize this new data, quoting one scientist who insists there is nothing to see here, move on! The trouble is that there is plenty to see here. Our knowledge of the climate remains very incomplete.”

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11/15/12, “Little Change in Drought Over 60 Years,” Roger Pielke, Jr.

“A new paper out in the current issue of Nature finds little evidence to support claims that drought has increased globally over the past 60 years.”…





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