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The University of Southampton

Southampton scientists predict the potential for a global temperature increase of four degrees and its implications

Published: 29 November 2010
‘Four degrees and beyond'
The report looked at the potential challenges facing a world that warmed by 4°C or more

What would be the potential challenges facing a world that warmed by 4°C or more? This question is addressed by scientists from the University of Southampton who have contributed to a special issue of Royal Society’s Philosophical Transactions published today (29 November).

‘Four degrees and beyond: the potential for a global temperature increase of four degrees and its implications’ provides an initial picture of the challenges facing a world that warms by 4°C or more.

The papers within the issue argue for renewed efforts to reduce emissions to minimise the chances of high-end climate change and the need for accelerated and focused research that improves understanding of how the climate system might behave under a +4°C warming, what the impacts of such changes might be, and how best to adapt to what are likely to be unprecedented changes in the world we live in.

The Southampton paper ‘Sea-level rise and its possible impacts given a “beyond 4 degree world” in the 21st Century’ looks at the impact of sea-level rises and what we need to do to adapt for this possible future.

Professor Robert Nicholls, who is the lead author of the paper, says: “Climate-induced sea-level rise remains highly uncertain, particularly the contribution from large ice sheets. A pragmatic estimate of sea-level rise by 2100 for a temperature rise of 4°C or more over the same time frame is between 0.5m to 2m. Globally, if coastal defences are not strengthened and upgraded to cope with these conditions, it may result in the forced displacement of up to 187 million people over the century, equivalent to 2.4 per cent of the global population.

“Protection is costly with up to 0.02 per cent of global domestic product needed. In response, we need to continue to monitor and better understand the processes that contribute to sea-level rise, mitigate and adapt for the long-term future.”

The 2009 Copenhagen Accord recognised the scientific view “that the increase in global temperature should be below 2 degrees Celsius” despite growing views that this might be too high. At the same time, the continued rise in greenhouse gas emissions in the last decade, and the delays in a comprehensive global emissions reduction agreement, has made achieving this target extremely difficult, arguably impossible, raising the likelihood of global temperature rises of 3 or 4°C within this century. Despite this, there are few studies that assess the potential impacts and consequences of a warming of 4°C or greater in a systematic manner.


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