Nature Climate Change | Climate Feedback

4 Degrees and Beyond: To flee the sea, or not to flee?

Immersing yourself in the impacts of extreme climate change can give rise to a certain amount of gallows humor. Conversation among my dinner companions last night turned to whether this week’s 4 Degrees and Beyond conference or March’s Copenhagen Climate Congress provided “more apocalypse for your conference fee”. The far more serious question, of course, is how much upheaval and human suffering would come with the substantial warming that delegates here are contemplating. Some interesting talks today looked at the facets of sea level rise and population displacement.

Stephan Rahmstorf of the Potsdam Institute for Climate Impacts Research had an intriguing update on a 2007 Science paper in which he’d come up with a new method for projecting sea level rise. Rahmstorf throws out any attempt to use complex climate models on this controversial problem and instead starts from scratch, with observed relationships between temperature rises and sea level rises. Now, working with Martin Vermeer of the University of Technology in Helsinki, he’s upgraded the extremely simple equation he used in 2007 to an only slightly less simple equation – one that takes account of the rate of warming and the amount of water that humans sequester in reservoirs. They use this to reconstruct a remarkably faithful record the last millennium’s sea levels.

Turning it to IPCC temperature projections, the team finds that sea level rise by 2100 could range, depending on the emissions scenario, from 0.75 to 1.9 metres, and a 4-degree world would likely see 0.98 to 1.3 metres of rise this century. A caveat: the recent sea-rise data that inspired and calibrated this equation and the past data that it explains don’t include the full effects of melting ice sheets that could lie ahead. That means 0.75 to 1.9 metres may be a conservative estimate.

But if we’re concerned with how creeping seas affect coastal populations, the amount of rise is not the only matter to settle. This was a key argument made by Francois Gemennes of the Institute for Sustainable Development and International Relations in Paris. Gemennes’ talk was based on a study of environmentally induced migration that I covered earlier this year. When it comes to climate refugees, he says, the numbers that are often tossed around – such as 200 million new migrants by 2050 – are based on the assumption that greater climate impacts will push more people around. What they aren’t based on is empirical data about how populations respond to environmental change. But according to the recent EACH-FOR project – the first global-scale survey of environmental migrants – the size of impacts isn’t the crucial variable at all: migration largely depends on policies making it possible for people to react to impacts by migrating. In particular, Gemennes argues, the poorest and most vulnerable will not be able to migrate unless they are given resources and exit routes – if we don’t encourage migration as an adaptation strategy, they’ll be trapped in the frying pan (or flooding delta).

The next event of the conference is a panel discussion on “4 degrees of climate change: alarmist or realist?”, which I’ll be tracking over on Twitter. Follow @annabarnett.

Anna Barnett

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