Temperatures go to extremes

Liz Kalaugher in Environmental Research Web: The average severity, length and number of heat waves are set to increase this century, according to analysis by US researchers. What's more, temperatures, uncertainty and geographic variability will all be higher than predicted by climate models.

"Over the current decade (specifically, for eight years from 2000 to 2007), the globally-averaged intensity of heat waves calculated from observations is higher and shows a more increasing trend compared to even the worst case projections from climate models," said Auroop Ganguly of Oak Ridge National Laboratory, US. "Increased trends point to the urgency of international and domestic policy negotiations for reducing emissions."

Ganguly and colleagues at Oak Ridge, the University of Notre Dame, and the US National Center for Atmospheric Research used ensemble simulations from a global earth systems model to analyse bias and uncertainty. They compared this data with observations for 2000–2007.

"The larger uncertainties, both at global and regional scales, suggest that policymakers and stakeholders may face a more complex task to decide the various societal cost-benefit trade-offs during decisions on climate related mitigation and adaptation related spending," said Ganguly. "Uncertainty is not an excuse for inaction, but an opportunity for more cautious and risk-informed decisions."

On the one hand, says Ganguly, increased uncertainty may imply a worst-case where temperature extremes are much more severe and frequent that even the most dire projections. "This implies a need to plan accordingly for a much higher worst-case, for example where human lives may be involved (e.g. consider the human mortality from the Paris and Chicago heat waves)," he said. "On the other hand, the larger uncertainty may also imply that the temperature extremes may not be as severe or frequent as we thought from the mean projections."…

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