Vayu: Climate change can make cyclones more destructive

Bengaluru Jun 12: Cyclone Vayu will strike coastal areas of Gujarat in next 48 hours. This could be one of the strongest cyclone to slam northwestern India in last many decades. This could be destructive too. Do you know what makes cyclones more destructive? Answer is Climate Change. There is increasing scientific evidence of the link between climate change and cyclones, including evidence on changes to cyclones in the Arabian Sea.

Climate change can make cyclones more destructive in several ways. According to the scientists warmer atmosphere can hold more moisture means huge amount of water get stored in clouds drives extreme rainfall during cyclones, increasing the threat of flooding. Not only this, the sea-level rise increases storm-surge damage and flooding for coastal communities. Higher ocean temperatures can make cyclones more powerful. There is some evidence that cyclones, including the most powerful storms, are becoming more common in the Arabian Sea.

Air pollution, caused by human activities, may also be strengthening cyclones in the Arabian Sea. This is because air pollution weakens the forces that can otherwise prevent cyclones from forming.

Dr James Kossin, Atmospheric Research Scientist, National Oceanic and Atmospheric Administration said, "There is evidence that air pollution over the Arabian Sea has caused a reduction of the wind shear that serves to weaken cyclones during the pre-monsoon months. When this is combined with warming oceans, which helps cyclones become stronger, there are two potential human-caused factors that are allowing Arabian Sea cyclones to get stronger than they would have been."

Scientists predict that rainfall from cyclones will increase with continued climate change. Means in future we could see more destructive cyclones.

Global sea levels have already increased about 19cm as a result of climate change. The rate of sea-level rise varies around the world and the North Indian Ocean has risen more quickly than other places in recent years. Sea-level rise increases the height of waves and storm surge, relative to the land. A small vertical increase in sea level can lead to a very large increase in the distance inland that storm surges can reach. Higher ocean temperatures can make cyclones more powerful , by increasing the potential energy available to them.

Arabian Sea gets warmer

This may be a factor in Cyclone Vayu, which has passed through waters in the Arabian Sea where the sea-surface temperature was more than 1°C warmer than the historical average (see image below). Globally, ocean temperatures have increased dramatically as a result of climate change. Global warming heats both the sea surface and the deep water, creating ideal conditions for a cyclone to become more powerful.

Higher sea-surface temperatures mean that cyclone wind speeds can increase . The strongest cyclones have become more common across the world, including in the North Indian Ocean, and scientists project that climate change will continue to make the strongest cyclones more powerful. Sea surface temperatures in the Arabian Sea during the formation of Cyclone Vayu was recorded higher that the previous.

Greenhouse gas emissions continue

There is some evidence that cyclones, including the most powerful storms, are becoming more common in the Arabian Sea. The number of days in which there was a cyclone in the basin was nearly three times higher from 1992-2008 compared with 1979-91, according to a 2011 study . This is because more storms started, rather than because storms lasted longer. A 2017 study found that human-caused global warming has made extremely severe late-season cyclones more common in the Arabian Sea. Globally there is no clear evidence that cyclones are becoming more common.

According to a study done in 2012, the tropical cyclones in the Arabian Sea will become 46% more frequent this century if greenhouse gas emissions continue to rise, particularly during peak-monsoon season.