The last several months have been a microcosm of why climate change is the public policy problem from hell. Several scientific developments have come to light, any of which on their own should have inspired massive action around the globe. But because the projected effects are so complicated and far in the future, the political impact has been nil.
The latest study comes from Stefan Rahmsdorf and colleagues in the journal Nature Climate Change. They've done a study on the Atlantic meridional overturning circulation, the system of currents of which the Gulf Stream is an important part. This system appears to be weakening rapidly, which may explain the shocking cold measured in the ocean south of Greenland — perhaps the only part of the entire world that experienced record cold last winter.
There is not very good or extensive data on Atlantic circulation, but Rahmsdorf and his team constructed a proxy data reconstruction going back to 900 AD. His conclusion:
This shows that despite the substantial uncertainties in the proxy reconstruction, the weakness of the flow after 1975 is unique in more than a 1,000 years, with at least 99 percent probability. This strongly suggests that the weak overturning is not due to natural variability but rather a result of global warming. [RealClimate]
These Atlantic currents are part of a global system of ocean circulation, driven by wind, temperature, and changes in salinity. As the Gulf Stream flows north, for instance, it cools through evaporation, which makes it relatively more salty. A decrease in temperature and an increase in salinity make water more dense, which causes it to sink towards the ocean floor, pushing along slower currents on the ocean floor that eventually reach the surface again. Such currents keep places like Britain and Norway warmer, while seeding tropical waters with critical nutrients.
The massive melting happening on Greenland is a likely explanation for this weakening trend. Land glaciers are made of fresh water, so when they melt, they dilute the salinity of the surrounding ocean — thus throwing a wrench straight into the circulatory mechanism.
Many write-ups of this research used the action-shlock film The Day After Tomorrow as a hook, but a better popular reference is Kim Stanley Robinson's Science in the Capital series. Robinson always does meticulous research, and the second book has a solid version of what might happen if the Gulf Stream were to collapse suddenly. Without it, there is a recurrence of the Younger Dryas, with most of Europe and the Eastern Seaboard experiencing an extremely cold winter, while the rest of the earth continues to warm.
Meanwhile, California is experiencing the opposite problem: extreme heat and drought. Its water storage is system is down to perhaps three years' supply if the drought doesn't break. Whether this particular drought can be tied to climate change with total certainty is disputed, though largely beside the point — as David Roberts points out, the thing to remember is that more warming means more droughts generally.
All this comes on the heels of two studies just in the last couple months projecting massively accelerated melting of Antarctica over the coming decades. All told, something like 20 feet of sea level rise due to Antarctic melting is now likely locked in. It may take centuries to fully shake out, but given the amount of capital invested in, say, New York City, one would imagine this would be grounds for swift action.
But these studies have had precisely zero impact on the political discourse. Instead, climate denier Ted Cruz has announced he is running for president, while Florida Gov. Rick Scott has banned use of the phrase "climate change" among state employees.
The only people actually doing anything constructive are the water managers in California, who have been forced into desperate action. But nobody is changing public policy to attack the root cause of all this — carbon dioxide emissions. It ought to be a reminder that even if the world doesn't collapse overnight like in The Day After Tomorrow, the long-term negative effects can still pile up at alarming rates.