The stories keep coming in about how past reports used by the IPCC have over-estimated or, less politely, exaggerated the extent and impact of climate change.

The latest claim to fall is about the severity of drought. In a warming climate there will be less rain and more evaporation leading to longer and more severe droughts. Indeed the drought that afflicted much of eastern Australia and which ended last year was incontrovertible proof of climate change.

It turns out that the index used for estimating the effect of drought was flawed, and in fact there has been no significant change in drought around the world in over 60 years.

So let's see. The world temperature hasn't increased in 16 years. The intensity and number of tropical storms has actually declined in the last few decades- Sandy notwithstanding. And now droughts haven't changed in 60 years.

So where is this catastrophic climate change we hear so much about?

From the ABC:

Drought 'overestimated by faulty index'

Many agricultural and climate experts have overestimated the past impact of global warming on drought due to flawed calculations, say researchers.

Associate Professor Michael Roderick, of the Australian Research Council Centre of Excellence for Climate System Science, and colleagues, report their findings today in the journal Nature.

"Here we show that the previously reported increase in global drought is overestimated," write Roderick and colleagues.

According to the 2007 Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), there have been more intense and longer droughts observed over wider areas since the 1970s, particularly in the tropics and subtropics.

"Increased drying linked with higher temperatures and decreased precipitation has contributed to changes in drought," the report says, quoted by Roderick and colleagues.

Roderick says such assessments of historical drought trends have relied on what is known as the Palmer Drought Severity Index (PDSI), developed in the US.

This index has also been used by government agencies, for example in the US, to estimate the severity of drought and to allocate financial aid.

But, he says, the index oversimplifies the effect of global warming by incorrectly assuming that increasing temperatures will cause more evaporation that will dry out the soil.

"Water doesn't necessarily evaporate faster as the temperature goes up. It depends on the details. And the details are all important here," says Roderick, a land surface specialist and biophysicist.