Economic costs of rising seas will be steeper than we thought, unless we prepare

Rising seas that swamp cities and coastal infrastructure could cost the world more than 4 percent of the global economy each year by 2100 — far more than previously estimated — unless urgent action is taken both to reduce greenhouse gas emissions and to prepare for such impacts from climate change, a new study finds. 

That worst-case scenario, which assumes that large amounts of polar ice will melt, could come to trillions of dollars. That’s “not peanuts,” says Thomas Schinko, a climate economist and deputy director of the Risk and Resilience program at the International Institute for Applied Systems Analysis in Vienna. “This would lead to a completely different world.” 

Given the risks, it’s hard to imagine that people won’t make any effort to adapt to a world with more flooding and coastal erosion, Schinko says. So that worst-case scenario is “not a very realistic scenario.” But regardless if the 4 percent global loss actually materializes, he says, the shocking number should show policy makers what could happen if they don’t act soon.

If countries lower greenhouse gas emissions enough to prevent the global temperature from rising more than 2 degrees Celsius above preindustrial levels, but do nothing else to prepare for rising seas, costs are projected to be more than 3 percent of global gross domestic product each year by 2100, the report says. But if countries lower emissions and prepare for sea level rise, costs can be limited to about 0.4 percent of global GDP or less, Schinko and his colleagues found. 

The study, published January 14 in Environmental Research Communications, goes beyond previous studies that estimated about 1.3 percent of global GDP in losses from seas rising on average by up to a meter (SN: 8/15/18). But where previous studies relied on one type of economic model, the new study uses three different types of macroeconomic models to test how different energy policies and emissions scenarios might play out on the global economy — as well as in specific countries — over the next eight decades. 

The researchers also considered how those economic impacts might change if coastal communities prepare for the increased risk of inundation, for example, by building dikes or sea walls (SN: 8/6/19). Previous studies had not taken all of these factors into account simultaneously. The team’s computer simulations adjusted as time went on, including local sea level rise changes and impacts from earlier years in estimating costs for later years. And the team looked at the economic effects of direct losses such as destroyed infrastructure, as well as indirect costs that can ripple through the economy, such as job losses and disrupted supply chains that can result from damage to businesses. 

Those models show that, regardless of the emissions scenario, global GDP losses will probably be relatively low overall through 2050, amounting to less than 0.4 percent annually, on average. But then, costs start to escalate — more or less depending on how much the world does to rein in climate-warming emissions and prepare for rising seas. 

The bottom line is, Schinko says, is that if we don’t do anything now, the costs and the effects of rising seas will skyrocket over the latter half of this century. “If we embark on the wrong trajectory, the impacts will be substantial.”

What’s more, “in this study, we’re only talking about the economic impacts of coastal flooding due to sea level rise, not droughts or wildfires … not salinity intrusion or loss of land” or other hazards like severe storms, Schinko says. Damages from climate change overall could be significantly worse. 

Losses from sea level rise would be spread unevenly across the world. China, for example, could lose up to 12 percent of its GDP each year by 2100; for China’s 2019 GDP, that amounts to $1.7 trillion. Losses in Japan could hit 8 percent annually; Europe, up to 6 percent annually, according to the report. 

The researchers note that their study still falls short of estimating the true cost of rising seas. For example, flooding from hurricanes and typhoons isn’t well represented, says study coauthor Daniel Lincke, a computer scientist and researcher at the Global Climate Forum in Berlin. 

Also not well-represented yet are compound floods — flooding made worse by additional high tides or heavy rainfall — which are probably the biggest problem arising from sea level rise, says coastal engineer Robert Nicholls, director of the Tyndall Centre for Climate Change Research at the University of East Anglia in Norwich, England. 

And of course, sea level rise projections themselves are a moving target. Projections based on ice melt, depending on how much greenhouse gases the world emits, vary from 25 centimeters to close to a meter by 2100. But that could change, as climate change simulations become increasingly sophisticated in incorporating more expected impacts from warmer atmospheric temperatures (SN: 1/7/20). 

Data that go into all of these models are getting better all the time, Lincke says. In just the last few months, researchers have tripled the number of people now living in areas likely to be inundated by floods over the next century, based on better elevation data (SN: 10/29/19). Studies have also revised value estimates for infrastructure and assets in floodplains around the world, revised population maps and examined changes in ocean circulation patterns that could make a big difference in sea level projections. 

The economic models used in the newest study took these revisions into account, as well as data about what’s actually happening now in coastal communities, Lincke says. Some coastal communities are doing nothing, while others are taking action to deal with climate-related flooding, for example, by building sea walls or moving expensive infrastructure (SN: 8/6/19). 

This preparation is key, researchers say. The world already is “beginning to see impacts — things like nuisance flooding along the East Coast of the U.S.,” Nicholls says. Even if countries manage to drastically curb their carbon emissions at this point, “seas will continue to rise. You can’t just turn off the tap. We have to prepare.”