Sea level rise: the worst-case climate change scenario

Amidst global warming, heat is the leading cause of sea water’s thermal expansion, which causes its volume to expand as it gets warmer. Warming also accelerates the surface melting of ice sheets and glaciers, which contributes 25% to the sea level rise. But in the last five years, ice melt from the ice sheets and mountain glaciers has overtaken global warming as the root cause of rising sea levels. The ice sheets in Greenland and Antarctica, whose melting rates are rapidly increasing, have raised the global sea level by 1.8 cm since the 90s and match the Intergovernmental Panel on Climate Change’s (IPCC) worst-case climate warming scenario.

According to a new study from the University of Leeds and the Danish Meteorological Institute, by the end of the century, the ice sheets are predicted to have raised sea levels by an additional 17 cm, exposing another 16 million people to yearly coastal flooding. Since the 90s, satellite observations over the ice sheets have shown that Antarctica’s ice-sheet melting has raised sea levels by 7.2 millimetres, while Greenland has added 10.6 millimetres. Since 1992, Greenland has lost 3.8 trillion tonnes of ice, which has caused the global sea level to rise by 10.6 millimetres. In the past ten years, ice loss has increased seven times, from 33 billion tonnes year in the 1990s to 254 billion tonnes annually.

The most recent data also reveals that the world’s oceans are rising by 4 millimetres annually. Although the scientists anticipated the ice sheets would lose increasing amounts of ice in response to the warming of the oceans and atmosphere, the rate at which they are melting has accelerated faster than they could have imagined.

The results are published in the journal Nature Climate Change. It contrasts calculations from climate models with the most recent findings from satellite surveys from the Ice Sheet Mass Balance Inter-comparison Exercise. The scientists warned that the ice loss rate on the ice sheets matches that predicted by the worst-case scenarios for global warming in the fifth assessment report by the IPCC. The melting is overtaking the estimates from the climate models, and the coastal population is in danger of being unprepared for the risks posed by sea level rise.

Sea level rise from the ice sheets alone should increase by an additional 17 cm if ice sheet losses following our worst-case climate change projections. The frequencies of storm-surge flooding in many of the biggest coastal cities globally will more than quadruple. The sea is rising for reasons other than just Antarctica and Greenland. Many glaciers have started to melt or vanish entirely in recent years. This indicates that the primary cause of sea level rise is now, melting ice. On current trends, Greenland ice melting will cause 100 million people to face floods each year by the end of the century, so 400 million in total due to rising sea levels. Several Asian megacities may face significant risks by 2100. Apart from Chennai and Kolkata, other Asian cities such as Yangon, Bangkok, Ho Chi Minh City, and Manila are also at risk.