Climate change: a failure to forecast
Gwynne Dyer says a few nasty surprises may be in store as we deal with the 'unknown unknowns' of melting sea ice and climate change
It's no surprise we will have a record minimum of ice cover in the Arctic Ocean at the end of this summer melt season. It's already down to around 4million square kilometres, with a least another week of melting to go, but this is what you might call a "known unknown". Scientists knew we were losing the ice cover fast; they just didn't know how fast.
I'm no fan of Donald Rumsfeld, the former US defence secretary, but I never had a problem with the distinction he made between "known unknowns" and "unknown unknowns" when discussing intelligence data. He was mocked in the media for using such jargon, but there really is a difference.
A "known unknown", in the case of the Arctic Ocean, is how long it will be before the entire sea is ice-free at the end of each summer. The 2007 report of the Intergovernmental Panel on Climate Change talked about that happening some time in the second half of this century, but it couldn't be more specific. A "known unknown", in other words.
As for the impact that an ice-free Arctic Ocean might have on climates elsewhere, it would obviously accelerate the global warming trend, but beyond that there wasn't much to go on. This was the territory of the "unknown unknowns": big things might happen to the complex atmospheric system of the planet, but nobody knew what.
Now we begin to see the consequences. The polar jet stream, an air current that circles the globe in the higher northern latitudes and separates cold, wet weather to the north from warmer, drier weather to the south, is changing its behaviour.
In a paper in the journal Jennifer Francis of Rutgers University and Stephen Vavrus of the University of Wisconsin-Madison offered a hypothesis that may explain why world grain prices are rising fast.
