Researchers ponder a 4°C temperature rise

In September 2009, scientists concerned over the lack of information available on the high-end scenarios of global warming held a conference at Oxford to pool their insights into the challenges the world will face if global temperatures rise by 4°C or more. Building on the information collected there, organiser Mark New and colleagues have now compiled a themed issue of the Philosophical Transactions of the Royal Society, entitled ‘Four degrees and beyond: the potential for a global temperature increase of four degrees and its implications’, which was released on the first day of the Cancún climate change meeting. The 13 contributions cover issues ranging from the climate forecasts to the question of if and how a catastrophic temperature rise can be averted, and, if it can’t be averted, how it will affect specific areas such as population movements, agriculture, water availability, forests, etc. The climate prognosis, as analysed by Richard Betts from the Met Office in Exeter, UK, seems to suggest that 4°C warming may not be that far away. A realistic scenario assuming that the current reliance on fossil fuels continues, but with little positive carbon-cycle feedback (such as methane released from deep-sea methane hydrate reservoirs as the oceans warm up), arrives at 4°C by the 2070s. Adding in carbon-cycle feedback, the threshold could be reached by the early 2060s. This prediction is consistent with the IPCC’s 2007 Assessment Report, which predicted warming of between 1.6 and 6.9°C by the end of the 21st century. So, if a 4°C temperature increase could be upon us within 50 years from now, we should better know what challenges we and our descendants are going to face. Rising sea levels are among the most often cited consequences of climate change, but they are also notoriously difficult to predict, due to the vagaries of melting ice sheets. Even when taking a 4°C temperature increase as given, the sea-level change associated with that could range from 0.5 metres to 2 metres, according to Sally Brown’s Researchers ponder a 4°C temperature rise News focus