Worst case scenarios of sea level rise, and why scientists and policymakers consider them

Robert McSweeney in the Carbon Brief: Sea levels could rise by a maximum of 190 centimetres by the end of the century, according to a new study, which examines a worst case scenario for sea level rise. In reality, the amount of sea level rise we get is likely to be less than that. But scientists and policymakers examine such 'worst case' scenarios to safeguard against climate risks.

With 10 per cent of the world's population living less than 10 metres above sea level, the threat of  coastal flooding is significant. The Intergovernmental Panel on Climate Change (IPCC) expects sea level rise to cause a ' significant increase' in sea levels extremes and the risk of coastal flooding.

The new study, published in  Environmental Research Letters, considers the assessment of 13 ice sheet experts. They conclude that the contribution from ice sheets is likely to be greater than projected by the IPCC. The paper suggests that sea levels could rise by as much as 190 cm this century.

Projections of sea level rise are typically constructed by working out the contribution to sea level rise from different  factors. The biggest contribution is from water expanding as it warms, followed by melting glaciers, then melting ice sheets on Greenland and Antarctica.

The crucial question for sea level rise this century is how much ice will be lost from the ice sheets, the authors argue. But it remains one of the largest uncertainties. In its Fifth Assessment Report (AR5), the IPCC  says there isn't sufficient evidence for them to give probabilities of large-scale losses of ice sheets.

The new study uses expert judgement to consider areas of ice sheet loss that are often not included in the sea level  models that the IPCC bases its assessment on. They then combine these judgements with the methods used in AR5 to produce their upper-limit figure of 190 cm....

A 2008 FEMA photo by Patsy Lynch of Hurricane Ike debris in Port Arthur, Texas