Study suggests Chennai, Kolkata particularly vulnerable to sea level rise

A new study suggests that the rise in sea level this century may have a disproportionate impact on certain Asian megacities, as well as western tropical Pacific islands and the western Indian Ocean.

The research team identified several Asian megacities that could face significant risks by 2100 if greenhouse gas emissions continue at high levels: Chennai, Kolkata, Yangon, Bangkok, Ho Chi Minh City, and Manila.

The study, published in the journal Nature Climate Change, examined the effects of natural sea-level fluctuations on the projected sea-level rise due to climate change by mapping sea-level hotspots globally.

Scientists have long known that sea levels will rise with increasing ocean temperatures because of water expansion and melting ice sheets. However, this study differs by incorporating naturally occurring sea level fluctuations caused by El Nino or changes in the water cycle, known as internal climate variability.

By using a computer model of global climate and a specialised statistical model, the scientists determined how these natural fluctuations can amplify or reduce the impact of climate change on sea level rise along certain coastlines.

The study showed that internal climate variability could increase sea level rise in some locations by 20-30 per cent more than what would result from climate change alone, exponentially increasing extreme flooding events.

For instance, in Manila, coastal flooding events are predicted to occur 18 times more often by 2100 than in 2006, based solely on climate change.

However, in a worst-case scenario, they could occur 96 times more often based on a combination of climate change and internal climate variability.

The study also found that internal climate variability will also increase sea level rise along the west coasts of the US and Australia.

The research utilised simulations performed with the Community Earth System Model, which is based on the National Centre for Atmospheric Research (NCAR). The simulations presume that society will continue to emit greenhouse gases at a high rate throughout this century.

The paper notes that the estimates of sea level rise come with considerable uncertainties due to the complex and unpredictable interactions in Earth’s climate system.

Nonetheless, the authors emphasise the need for society to be aware of the potential of extreme sea level rise to develop effective adaptation strategies.

NCAR scientist Aixue Hu, who co-authored the paper, said, “The internal climate variability can greatly reinforce or suppress the sea level rise caused by climate change.”

Hu added, “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 per cent of what is due to climate change alone, thus posing significant risks of more severe flooding to coastal megacities and threatening millions of people.”

With inputs from PTI