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SOURCE: Science News

DATE: August 15, 2018

SNIP: Even if humankind manages to limit the release of carbon dioxide enough to keep global warming to an average 2 degrees Celsius above preindustrial levels — which is highly unlikely — seas will still rise by a global average of about 20 centimeters by 2050, if not more. That’s enough to more than double the frequency of flooding in the tropics, where Mumbai is located, according to a 2017 paper in Scientific Reports.

Global losses from coastal flooding may surpass $1 trillion annually by 2050 unless coastal cities prepare, Hallegatte’s team says. That projection is actually conservative, because it doesn’t include damage from other climate-related flood risks such as heavier rains and stronger storms.

“For an individual, it doesn’t matter if the water is coming from sea rise or a storm surge or the clouds, a flood is a flood,” Hallegatte says. “Cities should be looking … at one-meter sea level rise, at least. Because the cost of failure is so big, you need to have a plan for the worst-case scenario.”

“This is a battle that we are currently losing,” says Princeton University climatologist Michael Oppenheimer, a coordinating lead author of the Intergovernmental Panel on Climate Change’s special report on oceans, cryosphere and climate change, due out in September 2019. “Sea level rise and the flood heights are only going to increase …for the foreseeable future.”

The annual monsoon, the seasonal shift in winds that brings flooding rains to Mumbai, adds an extra layer of uncertainty to projecting how much flooding will accompany sea rise, he says. The future of this South Asian weather system has been difficult to predict, thanks in part to the mysterious influence of the Indo-Pacific Warm Pool. It’s Earth’s largest region of warm surface seawaters spanning the midocean region between the western Pacific and the eastern Indian oceans. That warmth partly fuels monsoon storm clouds.

Still, most studies suggest that the monsoon rains will increase. “Uncertainty is not an excuse [for inaction] at this point,” Oppenheimer says. “People need to get moving.