JoNova

A science presenter, writer, speaker & former TV host; author of The Skeptic's Handbook (over 200,000 copies distributed & available in 15 languages).



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Nature paper: Global droughts unchanged in 60 years

How many images have we seen of drought-stricken cracked land, or been told this is the future? How many headlines have suggested that global warming causes droughts?

Since the end of World War II humans have produced some 85% of all their CO2 emissions, but here is a new study showing that for all those emissions, and for all that warming, droughts back then were just as bad globally as they are today.

Essentially, researchers thought that the Palmer Drought Severity Index (PDSI) was the way to measure global drought levels, and they thought that warming would increase global drought conditions. But the PDSI considers only temperature, not humidity, sunlight and wind. This paper shows that when these factors are included, worldwide drought is about the same now as it was in 1950.

Researchers are finally accounting for the fact that a warmer world usually means more evaporation (especially from the ocean) and thus more rain. It’s good to see that someone has crunched those complex numbers on a global scale. Credit to Sheffield, Wood & Roderick.

Figure 1 | Global average time series of the PDSI and area in drought. a, PDSI_Th (blue line) and PDSI_PM (red line). [...]

Droughts might not be due to carbon-dioxide, says CSIRO

Still in the theme of Shock!-The-Media-IS-Reporting-The-News: The Canberra Times announced on it’s front page that CSIRO is not so sure that droughts are due to increased carbon dioxide. Only a few months ago, they announced the exact opposite.

September 2009: A three-year collaboration between the Bureau of Meteorology and CSIRO has confirmed what many scientists long suspected: that the 13-year drought is not just a natural dry stretch but a shift related to climate change.

Jan 2010: One of the report’s co-authors, hydrologist David Post, told The Canberra Times there was ”no evidence” linking drought to climate change in eastern Australia, including the Murray-Darling Basin.

Back in September, this long study was based on the old trick of using climate models and “subtracting” the natural causes to see what’s left. It’s also known as “Argument from Ignorance”. Since we can’t predict the climate five years in advance, obviously there are factors or weightings in those climate models that aren’t right. Ruling out “what we know” doesn’t prove anything at all, except that there is a lot we don’t know.

When David Stockwell analysed climate models and Australian droughts, he found that random numbers were more likely to predict droughts successfully. [...]