Is Global Warming Really Global Cooling?
In a November special issue of the journal Ecology, a group of scientists report that if current patterns of change in the Arctic and North Atlantic Oceans continue, alterations of ocean circulation could occur on a global scale, with potentially dramatic implications for the world’s climate and biosphere.
Charles Greene of Cornell University and colleagues reconstructed the patterns of climate change in the Arctic from the Paleocene epoch to the present. Over these 65 million years, the Earth has undergone several major warming and cooling episodes, which were largely mitigated by the expansion and contraction of sea ice in the Arctic.
When the Arctic cools and ice expands, the increase ice cover increases albedo. The resulting increased reflection of the sun leads to global cooling. Likewise, when ice sheets and sea ice contract and expose the darker-colored land or ocean underneath, heat is absorbed, accelerating climate warming. Currently, the Earth is in the midst of an interglacial period, characterized by retracted ice sheets and warmer temperatures.
As large portions of the polar ice cap break off and fall into the Arctic Ocean, large quantities of fresh water abruptly reduces the salinity. Continued exposure to such freshwater forcing, however, could disrupt global ocean circulation during the next century and lead to very abrupt changes in climate, similar to those that occurred at the onset of the last ice age.
“If the Earth’s deep ocean circulation were to be shut down, many of the atmospheric, glacial and oceanic processes that have been stable in recent times would change, and the change would likely be abrupt,” says Greene.
“While the ecosystem consequences of gradual changes in the ocean are somewhat predictable, all bets are off after such abrupt changes occur.”
These abrupt disruptions on a large scale could halt the Earth’s ocean currents and lead us into the next Ice Age.
