20 may 2013

Global warming continues; most extreme projections 'less likely'

Science | Environment

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A new study led by Oxford University concludes that the latest observations of the climate system's response to rising greenhouse gas levels are consistent with conventional estimates of the long-term 'climate sensitivity', despite a ''warming pause'' over the past decade. However, the most extreme rates of warming simulated by the current generation of climate models over 50- to 100-year timescales are looking less likely, according to the paper published online by Nature Geoscience.

Their findings, resulting from a broad international collaboration of scientists, are significant because they use the most up-to-date information on temperatures, energy flows and energy accumulation in the climate system available to the next Scientific Assessment of the Intergovernmental Panel on Climate Change, due to be finalised in September.

Dr Alexander Otto, from the Environmental Change Institute at the University of Oxford, said: 'Recent observations suggest the expected rate of warming in response to rising greenhouse gas levels, or 'Transient Climate Response,' is likely to lie within the range of current climate models, but not at the high end of this range.

'The eventual long-term warming after stabilization remains rather uncertain, but for most policy decisions, the transient response over the next 50-100 years is what matters.'

Professor Reto Knutti of ETH Zurich said: 'Clearly, new data helping to rule out more extreme scenarios for near-term rates of warming is welcome news, but even if the response is at the low end of the current range of uncertainty, we are still looking at warming well over the two degree goal that countries have agreed upon if current emission trends continue.'

Professor Jochem Marotzke of the Max Planck Institute for Meteorology in Hamburg said: 'It is important not to over-interpret a single decade, given what we know, and don't know, about natural climate variability. Over the past decade, the world as a whole has continued to warm, but the warming is mostly in the subsurface oceans rather than at the surface.'

Professor Piers Forster of the University of Leeds said: 'We know much more than we did only a few years ago how different factors, like global aerosol emissions, affect the global energy budget, and this new study draws out the implications.'