Major Tipping Points in the Earth’s Climate System and Consequences for the Insurance Sector
Arctic region received an increase in solar heat input at the surface, and there is up to a +5% per year trend in 3 some regions (10) . In the Beaufort Sea, North of Alaska, the annual solar heat input has increased by 3– 4 times, and warming ocean water intruding under the remaining ice pack is now contributing substantially to summer melt. In 2007 and 2008 there was three times greater melt from the bottom of the ice than in earlier years (11). Increased input of warmer ocean water from the Pacific (through the Bering Straits) is part of the problem (12, 13). The patterns of atmospheric (14, 15) and ocean (16) circulation have also contributed to record ice loss by flushing thick, ‘multi-year’ ice out of the basin, reducing the heat capacity of the remaining ice pack and making it more vulnerable to melting. Also, reductions in summertime cloud cover are causing more sunlight to fall on the ice (17). The observed changes in sea ice cover are more rapid than in all IPCC AR4 model projections (despite the observations having been in the mid-range of the models in the 1970s). In half of the models, the summer sea-ice cover disappears during this century (at a polar temperature of around 9 °C above 1980–1999). However, given the observations and further committed warming already ‘in the pipeline’, the Arctic could already be committed to becoming largely ice-free each summer, within the next few decades. Such a transition should be reversible in principle (18), although it would still be difficult to reverse in practice (because anthropogenic forcing would have to be reduced in the region). Recent work has shown that black carbon (soot) from fossil fuel and biomass burning (much of it from South East Asia) has been a major contributor to Arctic regional warming. It is deposited on the sea-ice, darkening it and accelerating melt. A decline in reflective sulphate aerosols in the atmosphere has also contributed significantly to warming, as have the relatively short-lived greenhouse gases ozone and methane. This offers some hope that mitigation of non-CO2 pollutants could help preserve the sea-ice.
2.2.3 Sea Level Rise from melting ice sheets and ice caps The main impact associated with melting of the Greenland Ice Sheet (GIS), West Antarctic Ice Sheets (WAIS) and small continental ice caps, is sea level rise. Hence we begin with a summary of expected combined sea level rise from these sources with further information on the individual components provided below that. Quick facts: Combined Sea Level Rise (SLR) from Greenland and West Antarctic Ice Sheets and continental ice caps Aggregate sea level rise IPCC (2007) chose not to include the uncertain contribution of changing mass of polar ice sheets in their projections of future sea level rise. As such, a ‘No Tipping’ scenario for global SLR from IPCC gives global SLR at around 0.15 m by 2050. There is a convergence on minimum global sea level change being of the order of 75 cm in 2100 and absolute maximum being of the order 2 m. On the basis of this, a ‘Tipping’ Scenario of around 0.5 m of global sea level rise by 2050 is a reasonable starting assumption. Technical details: Potential sea level rise from melting ice Combining Antarctica, Greenland and small ice caps, the maximum total contribution to sea level rise from melting ice is estimated at ~2 m this century (19). Yet paleo-data from the Eemian interglacial (up to ~2 °C globally warmer than present) indicate that it had peaks of sea level up to 9 m higher than present, and approached them with rates of sea level rise of up to 2.5 m per century (20). Thus, current upper limit estimates of sea level rise of ~2 m this century cannot be ruled out, as they have occurred in a world with temperatures and total ice similar to the present one.
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Also Donald K. Perovitch, personal communication regarding latest data.
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