A new study published in the journal Nature Climate Change has found that, by the end of this century, sea level rise may disproportionately affect several Asian megacities – such as Chennai, Kolkata, Yangon, Bangkok, Ho Chi Minh City, and Manila – as well as western tropical Pacific islands and the western Indian Ocean.
Scientists have long known that increases in ocean temperatures will lead to sea level rise, since water expands when it warms and melting ice sheets release more water into the ocean. However, studies have also indicated that such rises in sea levels will vary regionally because changes in ocean currents will direct more water to certain coastlines (including northeastern U.S.).
A notable aspect of this study is that it incorporates naturally occurring sea level fluctuations caused by El Niño or changes in the water cycle (a process called “internal climate variability”). By combining computer models estimating how the global climate may change in a high-emissions scenario with a specialized statistical model, the experts examined the extent to which these natural fluctuations might amplify – or, in some cases, reduce – the impact of climate change on sea level rise along certain coastlines.
The analysis revealed that, in some regions, internal climate variability could increase sea level rise by 20 to 30 percent more than climate change alone, thus leading to an exponential spike in extreme flooding events. In Manila, for instance, while coastal flooding events are predicted to occur 18 times more often by 2100 due to climate change alone, they could occur 96 times more often from a combination of both climate change and internal climate variability.
According to the researchers, although the complex and unpredictable interactions in our planet’s climate system create significant difficulties in reliably estimating sea level rise, it is critical for society to be aware of the potential of extreme sea level rise in order to develop effective adaptation strategies.
“The internal climate variability can greatly reinforce or suppress the sea level rise caused by climate change. In a worst-case scenario, the combined effect of climate change and internal climate variability could result in local sea levels rising by more than 50 percent of what is due to climate change alone, thus posing significant risks of more severe flooding to coastal megacities and threatening millions of people,” concluded study senior author Aixue Hu, a meteorologist and oceanographer at the National Center for Atmospheric Research (NCAR).
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