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Download issue (1.37MB PDF) Cover Page Executive Summary 1.Climate Change: a primer 2.What is dangerous climate change? 3.1.Causes of sea-level rise 3.2.Rates of sea-level rise in history 3.3.Ice sheet melting and catastrophic sea-level rise 3.3a.The Greenland Ice Sheet 3.3b.The West Antarctic Ice Sheet 3.3c.Future prospects for coastal environments 4.Gulf Stream shutdown 5.Conclusions 6.Sources and Further Reading

Issues in Risk Science Dangerous Climate Change: rising sea-levels and ocean circulation changes - Professor Bill McGuire Executive Summary Dangerous climate change is a legal term introduced by the UN in its 1992 Framework Convention on Climate Change (UNFCCC), which calls for the stabilisation of greenhouse gases so as to ‘prevent dangerous anthropogenic interference with the climate system’. In 2004, the European Climate Forum highlighted more specific indicators of dangerous climate change, including circumstances that could lead to global and unprecedented consequences, extinction of iconic species (e.g. the Polar Bear), loss of entire ecosystems or human cultures, a threat to water resources, and a significant rise in mortality rates. Dangerous climate change is likely to happen suddenly in response to the crossing of specific thresholds or achievement of so-called tipping points. Two major resulting threats relate to rapidly rising sea-levels and the shutting down of the Atlantic Thermohaline Circulation (ATHC) – the Gulf Stream and associated currents. Concerns about catastrophically rising sea-levels have increased in the light of recent observations of accelerated ice loss at the poles. The rate of melting of the Greenland Ice Sheet has doubled in the last 10 years, from 96 km3 in 1996 to 220 km3 in 2005, with three of the biggest glaciers draining the ice sheet doubling their rates of sliding seawards in the last 7 years. A local temperature rise of just 2.7° C (corresponding to a global rise of less than 2° C) is predicted to result in irreversible melting of the Greenland Ice Sheet and an eventual ~ 7 m sea-level rise. This threshold could be reached as early as 2050. Increased ice loss is also occurring in Antarctica, where the West Antarctic Ice Sheet is now losing about 150 km3 a year. Over the last 50 years, an area of ice shelves the size of Jamaica have broken up and melted, while on the Antarctic Peninsula, the Pine Island and Thwaites glaciers are now moving three times faster than 10 years ago. Melting of these glaciers alone would raise sea-levels by more than a metre, with complete melting of the West Antarctic Ice Sheet raising global sea-levels by ~ 5 m. Sea-levels are currently rising at ~ 3 mm a year, but if catastrophic melting of the Greenland and/or West Antarctic ice sheets occurs, some climate scientists now forecast a rise as high as 1-2 m this century and several metres by 2200. Another aspect of dangerous climate change involves the shutdown of the Gulf Stream and associated currents (making up the Atlantic Thermohaline Circulation or ATHC), which keep the UK and Europe up to 8 degrees warmer than comparable latitudes such as northern Canada and eastern Siberia. Climate models predict that if nothing is done to mitigate greenhouse gas emissions, one recent study estimated that the probability of ATHC shutdown this century could be higher than 50 percent. Recent measurements suggest, however, that the ATHC may have slowed by 30 percent since 1992. This could result in a 1° C fall in UK and European temperatures within 10 years, bringing a return to Little Ice Age conditions, while complete shutdown of the ATHC could result in a 4° C fall, with winter temperatures frequently far lower than minus 10° C within 5-6 years of shutdown.