In response to the Edge.org 2009 annual question, which this year was – What game-changing scientific ideas and developments do you expect to live to see? Laurence Smith, Professor of Geography and Earth & Space Sciences at UCLA, writes about abrupt climate change in West Antarctica and seven other sleeping giants:
We used to think climate worked like a dial – slow to heat up and slow to cool down – but we’ve since learned it can also act like a switch. Twenty years ago anyone who hypothesized an abrupt, show-stopping event – a centuries-long plunge in air temperature, say, or the sudden die-off of forests -would have been laughed off. But today, an immense body of empirical and theoretical research tells us that sudden awakenings are dismayingly common in climate behavior. …
The mechanisms behind such lurches are complex but decipherable. Many are related to shifting ocean currents that slosh around pools of warm or cool seawater in quasi-predictable ways. The El Niño/La Niña phenomenon, which redirects rainfall patterns around the globe, is one well-known example. Another major player is the Atlantic thermohaline circulation (THC), a massive density-driven “heat conveyor belt” that carries tropical warmth northwards via the Gulf Stream. … a THC shutdown nonetheless remains an unlikely but plausible threat. It is the original sleeping giant of my field.
Unfortunately, we are discovering more giants that are probably lighter sleepers than the THC. Seven others – all of them potential game-changers – are now under scrutiny: (1) the disappearance of summer sea-ice over the Arctic Ocean, (2) increased melting and glacier flow of the Greenland ice sheet, (3) “unsticking” of the frozen West Antarctic Ice Sheet from its bed, (4) rapid die-back of Amazon forests, (5) disruption of the Indian Monsoon, (6) release of methane, an even more potent greenhouse gas than carbon dioxide, from thawing frozen soils, and (7) a shift to a permanent El Niño-like state. Like the THC, should any of these occur there would be profound ramifications – like our food production, the extinction and expansion of species, and the inundation of coastal cities.
…the presence of sleeping giants makes the steady, predictable growth of anthropogenic greenhouse warming more dangerous, not less. Alarm clocks may be set to go off, but we don’t what their temperature settings are. The science is too new, and besides we’ll never know for sure until it happens. While some economists predicted that rising credit-default swaps and other highly leveraged financial products might eventually bring about an economic collapse, who could have foreseen the exact timing and magnitude of late 2008? Like most threshold phenomena it is extremely difficult to know just how much poking is needed to disturb sleeping giants.