Coastal flooding could hit 20% of world GDP by 2100 - study

Failure to rein in climate change and bolster sea defences could jeopardize up to a fifth of the world's economic output by the end of the century, as flooding threatens coastal countries worldwide, according to a study released on Thursday.

From Bangladesh and India to Australia and even Britain, rising sea levels already are leading to more frequent and extreme flood events. With climate change causing polar ice to melt and ocean waters to expand, economists have sought for years to put a figure on the future potential damage.

The latest effort, published Thursday in the journal Scientific Reports, paints one of the grimmest scenarios yet in estimating the economic fallout from sea rise if the world continues emitting greenhouse gases at the current rate.

Flood events that have typically occurred once in 100 years "could occur as frequently as once in 10 years" for much of the world, said the authors of the report, including researchers at the universities of Amsterdam, Melbourne and the Global Climate Forum.

This worst-case scenario would cost the world up to 20% of its annual gross domestic product, given the impact on buildings and other infrastructure, they said. Their estimates were based on factors including the populations and assets at risk, and models of tides, surges and sea levels around the world's coasts.

Based on estimated 2019 GDP, that currently comes to around $17.6 trillion.

However, the study's focus on the worst-case scenario - with high emissions and no flood preparations - may be unrealistic, said climate economist Thomas Schinko, deputy director of the Risk and Resilience research programme at the International Institute for Applied Systems Analysis in Vienna.

Already, "societies are reacting to changing coastal flooding risks all over the world," said Schinko, who was not involved in the new research. Though, "not all countries are equally well equipped to adapt."

The study used computer simulations that accounted for global tides, storm surges and wave data in gauging flood risks.

The bulk of the damage - 68% - would be caused by tide and storm events, rather than sea level rise itself. 

Areas that are now home to some 171 million would be affected, with extensive flooding expected in northwest Europe, including the UK and northern France, as well as in southeastern China, Australia's Northern Territories, Bangladesh and the US states of North Carolina and Virginia.

Schinko said the work should be seen as "a strong signal to the international policy scene to urgently strengthen the ambitions for climate change mitigation".