Lowering temperatures could be a slow processLiz Kalaugher, environmentalresearchweb, March 24, 2009
The European Union has set a target level of 2 °C to prevent "dangerous" climate change. But if greenhouse gas emissions continue at their current rates it's likely that such thresholds will be crossed, says a UK team. With that in mind, the researchers assessed how fast the system may be able to return to safer temperatures once emissions have been cut; the news is not good.
"We find that even for very large reductions in emissions, temperature reduction is likely to occur at a low rate," write the scientists from the UK Met Office, Centre for Ecology and Hydrology, and Manchester Metropolitan University in Environmental Research Letters.
The researchers used a state-of-the-art general circulation model to study the timescale needed for temperatures to return below the threshold. Then they used a simple climate model to provide uncertainty bounds for their calculations.
"We used the most complex type of model to look at temperature overshoot in aggressive mitigation scenarios because previously this had only been done using simpler types of model," Jason Lowe of the Met Office Hadley Centre told environmentalresearchweb. "However, once we proved the method, we also needed to use a simpler model ourselves to look at uncertainty. IPCC AR4 spent a lot of time looking at uncertainty in projections for scenarios of increasing temperature so it was natural that we extended our work to include uncertainty estimates of recovery time after the peak."
Lowe says the team's main result is its estimate of how uncertainty in key climate parameters, such as climate sensitivity, affects the recovery from peak temperature back below various threshold levels. Another key achievement is the use of a complex climate model to confirm a result previously seen in models of intermediate complexity – that recovery from peak temperatures may take long periods of time.
"The paper is policy-relevant because it shows that rather than just considering the probability of meeting or exceeding given temperature targets (like the EU 2 °C target), we should also take account of the length of time spent over the target if it is exceeded," said Lowe. "In other words, policy makers and scientists need to consider the resilience of systems and human systems – people – to temporarily experiencing high temperatures."
Now the researchers plan to look at how the temperature overshoot scenarios they considered affect key physical climate thresholds. They say they are already making progress on the impacts on tropical forests and the Greenland ice sheet.
Liz Kalaugher is editor of environmentalresearchweb
Link to article: http://environmentalresearchweb.org/cws/article/futures/38360