Certain Asian megacities and tropical Pacific islands may be disproportionately impacted by climate-induced sea level rise because of natural sea level fluctuations caused by events such as El Niño.
Led by the French National Centre for Scientific Research (CNRS) and University of La Rochelle and co-authored by the US National Center for Atmospheric Research (NCAR), the study mapped sea level hot spots around the globe and identified several Asian megacities that may face significant risks by 2100 if society emits high levels of greenhouse gases. This includes Chennai and Kolkata, India; Yangon, Myanmar; Bangkok, Thailand; Ho Chi Minh City, Vietnam; and Manila, Philippines.
Alongside the sea level rise from melting ice sheets, studies have indicated that sea level rise will vary regionally because shifts in ocean currents will likely direct more water to certain coastlines, including that of the Northeastern US. However, the new study incorporates naturally occurring sea level fluctuations caused by such events as El Niño and changes in the water cycle (internal climate variability). By using both a computer model of global climate and a specialized statistical model, the scientists could determine the extent to which 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% more than what would result from climate change alone, exponentially increasing extreme flooding events. In Manila, for example, coastal flooding events are predicted to occur 18 times more often by 2100 than in 2006, based solely on climate change. But, in a worst-case scenario, they could occur 96 times more often based on a combination of climate change and internal climate variability.
Internal climate variability will also increase sea level rise along the west coasts of the US and Australia. The study drew on a set of simulations conducted with the NCAR-based Community Earth System Model that assume society this century emits greenhouse gases at a high rate. The simulations were run at the NCAR-Wyoming Supercomputing Center.
The paper stressed that the estimates of sea level rise come with considerable uncertainties because of the complex and unpredictable interactions in Earth’s climate system. But the authors insist that it is critical for society to be aware of the potential of extreme sea level rise to develop effective adaptation strategies.
Aixue Hu, project scientist at NCAR and study co-author, said, “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% of what is due to climate change alone, thus posing significant risks of more severe flooding to coastal megacities and threatening millions of people.”
To view the complete study published in the journal Nature Climate Change, click here.
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