Climatology: Threatened loss of the Greenland ice-sheet

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The Greenland ice-sheet would melt faster in a warmer climate and is likely to be eliminated – except for residual glaciers in the mountains – if the annual average temperature in Greenland increases by more than about 3 °C. This could raise the global average sea-level by 7 metres over a period of
1,000 years or more. We show here that concentrations of greenhouse gases will probably have reached levels before the year 2100 that are sufficient to raise the temperature past this warming threshold.

At present, about half of the snow falling on Greenland melts and runs off as water, and the remainder is discharged in the form of icebergs. Climate change caused by higher greenhouse-gas concentrations is expected to produce both higher temperatures and greater precipitation, but most studies conclude that the increase in melting will outweigh the increase in snowfall1. For an annual average warming of more than 2.7 °C, the melting exceeds the snowfall – a situation in which the ice-sheet must contract, even if iceberg production is reduced to zero as it retreats from the coast.

For a warming of 3 °C, the ice-sheet loses mass slowly and over millennia might approach a steady state in a smaller inland form. For greater warming, mass is lost faster and the ice-sheet is likely to melt away. The most extreme scenario considered in the third assessment report of the Intergovernmental Panel on Climate Change (IPCC) involves a warming of 8 °C; in this case, most of the ice-sheet disappears over the next 1,000 years.

The magnitude of predicted global warming depends on the concentration of greenhouse gases and the climate response to these. We have calculated the development of Greenland’s temperature using IPCC scenarios in which atmospheric carbon dioxide concentration stabilizes at different levels over the next few centuries.

The lowest carbon dioxide concentration considered was 450 p.p.m. Given that this level is exceeded before 2050 in all of the IPCC report’s emission scenarios, and that carbon dioxide is not the only greenhouse gas, we conclude that the Greenland ice-sheet is likely to be eliminated by anthropogenic climate change unless much more substantial emission reductions are made than those envisaged by the IPCC. This would mean a global average sea-level rise of 7 metres during the next 1,000 years or more.

Without the ice-sheet, the climate of Greenland would be much warmer because the land surface would be at a lower altitude and reflect less sunlight. This conclusion can be drawn without detailed modelling. Even if atmospheric composition and the global climate were to return to pre-industrial conditions, the ice-sheet might not be regenerated, which implies that the sea-level rise could be irreversible.