Four degrees of global warming looms
2 October 2009, by Marion O'Sullivan
Climate experts hotly debated the implications of a much warmer future and ways to adapt to the changes at a conference in Oxford this week. Global temperatures could reach 4°C above pre-industrial levels before the end of this century and rising sea-levels could drown some small islands, if greenhouse gas emissions continue at current rates.
A Met Office study of trends in fossil-fuel use over the past 20 years, combined with findings of how carbon dioxide is absorbed by the oceans and forests, predicts that the 4°C rise could be seen as early as 2060.
Their climate model shows some extreme regional variations, such as a 10°C temperature rise in the Arctic, with varying degrees of warming and reductions in rainfall over western and southern Africa, Central America, the Mediterranean and parts of coastal Australia.
Dr Richard Betts of the Met Office Hadley Centre emphasised that are uncertainties in the model, particularly in the role of the carbon cycle, but also that the findings are significant. 'If greenhouse gas emissions are not cut soon then we could see major climate changes within our own lifetimes,' he said.
'The long-term future is irreducibly uncertain – but it always has been. Climate change is just another pressing risk... the biggest uncertainty is how the human race will react....' Dr Mark Stafford-Smith, Australian Commomwealth Scientific Research Organisation
Sea levels have risen by about 20cm in the last century and the rate is accelerated faster than expected. Professor Stefan Rahmstorf from Germany's Potsdam Institute believes that sea-level rise will continue in future even if we manage to stabilise temperatures 'Since 1993 the level has risen by 3.4 mm per year and the future is uncertain,' he said. 'At 4°C above pre-industrial levels we could see a 1.3m rise by 2100.'
Southampton University's Professor Robert Nicholls agrees that sea-level rise is a major threat that will continue for centuries, but argued that the effects will also depend on the level of exposure and what types of adaptation we put in place. 'We have already seen a 2m rise in sea levels in the 20th century, that have sunk due to subsidence...' he said. 'They are still there but they depend on dikes, water management, pumps to keep themselves dry.'
The cost of investing in protection from rising sea levels is huge, but Nicholls considers that adaptation rather than mitigation is more effective in reducing the socio-economic impacts. 'A better understanding of adaptation is essential,' he said. 'Especially for the most vulnerable areas – small islands, deltas, and places that are poor are where the challenges are greatest.'
People living in densely populated small island states, such as Tuvalu in the Pacific Ocean, are already dealing with the risks and implications of rapidly rising sea-levels. The predicted 4°C rise in global temperature will make them climate refugees.
The 4 degrees and beyond international climate conference, 28-30 September 2009, was held at the University of Oxford. It was organised by the Tyndall Centre, the Met Office and the University of Oxford.
The issues of deforestation, emissions from aircraft, shipping and energy use, carbon capture and sequestration, increasing numbers of wildfires, human health and safety, and the implications for agriculture and food security were among the many discussions during the three-day conference.
Audio files and slide presentations from the conference sessions are available at http://www.eci.ox.ac.uk/4degrees/programme.php
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