The upshot? Earth is already seeing some abrupt changes, like the fast retreat of summer Arctic sea ice. There’s also a real risk that other rapid and drastic shifts could follow in the coming decades if the Earth keeps warming — including widespread plant and animal extinctions and the creation of large “dead zones” in the ocean.
On the flip side, other drastic changes “are now considered unlikely to occur this century.” That includes shifts in Atlantic ocean circulation patterns that could radically alter Europe’s climate, as hyped in the disaster flick “The Day After Tomorrow.” Also unlikely this century: Collapsing ice sheets in West Antarctica that would push sea levels up very quickly, as well as sudden methane eruptions from the Arctic that could heat the planet drastically. Those doomsday scenarios are left to future generations.
The authors do emphasize, however, that scientists still don’t fully understand all the different ways the Earth’s climate can change in short order. There are lots of unknowns here. “Some surprises in the climate system may be inevitable,” they conclude, “but with improved scientific monitoring and a better understanding of the climate system it could be possible to anticipate abrupt change before it occurs and reduce the potential consequences.”
Here’s a longer rundown of some of the abrupt changes the new National Research Council report explores, as well as how probable they are to occur this century (I’ve ordered them from most likely to least likely):
— Sharp increases in extinction rates. A recent study in Science found that the world is on track to warm much faster than it has in the past 65 million years. That could require some species to shift habitats at an unprecedented rate.
(Source: Diffenbaugh and Field 2013)
This concept is known as the “velocity of climate change,” and the map on the right shows two different estimates of how quickly species would have to shift in order to maintain the climates of their current habitats (assuming they needed to).
Schematic of the major warm (red to yellow) and cold (blue to purple) water pathways in the North Atlantic subpolar gyre. (Woods Hole Oceanographic Institute)
Global Climate Change http://courses.dce.harvard.edu/~envre130
Environmental Justice http://courses.dce.harvard.edu/~envre145
Environment Ethics http://courses.dce.harvard.edu/~envre120