Pasadena (CA) - NASA reported on Tuesday that after years of research, a team of scientists have assembled data showing that normal, decade-long changes in Arctic Ocean currents are largely responsible for the major Arctic climate shifts observed over the past several years. These periodic reversals in the ocean currents move warmer and cooler water around to new places, greatly affecting the climate. While they are not ruling out the possibility of a continual warming trend, the rate at which the Earth is warming seems to be far more stable than the Arctic would indicate.
Coordinating out of the University of Washington and their Polar Science Center Applied Physics Laboratory in Seattle, director James Morison's team used a series of satellites to collect data over a period of time between 2002 and 2006. They also used deep-sea pressure gauges which monitor ocean circulation, salinity, pressure and temperature from the surface to the bottom of the ocean. The team measured the samples as representative columns, each of a cross-section or vertical tube in the ocean. They fed the data into a computer and observed the trends indicated over time. The graph on the left visualizes various increases and decreases in ocean data, specifically changes in bottom pressure indicating water weight.
The results have demonstrated that a known process called Arctic Oscillation, whereby ocean currents reverse their previous decade-long migration patterns from time to time, have been moving warmer and more saline water to places it had not previously gone. This natural cycle in oceanic currents has caused the significant changes in Arctic climate observed from the late 1970s through the 1990s. This pattern has allowed us to observe a greatly amplified effect over any natural warming trend which may be occurring (there is still no solid consensus on that issue).
The research team also discovered that the ocean currents have recently switched back to the route they took in the previous decades, prior to the significant warming seen throughout the 1990s. These new changes will likely put the Arctic regions back into a cooling cycle again, although it will likely take several years to be observed as changes on these immense scales, millions of cubic miles of water, take time.
Decade long cycles
The Arctic Oscillation effect was predicted by computer models early on. It's been observed now with hard data for decades. It is nothing short of a major atmospheric circulation pattern in the northern hemisphere. Changes in salinity and temperature alter the various chemistry of the ocean, resulting in changes in water weight as the saltier and cooler water is heavier. When huge volumes of water change their weight even slightly, enormous new patterns in ocean currents are the result. The team seems to have enough data over decades to demonstrate that everything we're seeing is the result of natural cycles.
According to the news release, the Arctic Oscillation was fairly stable until around 1970. At that point it began shifting in decade-long timescales. It eventually resulted in a type of counter-clockwise swirling pattern which significantly altered the Arctic climate in the 1990s. However, in the late 1990s it began stabilizing again and as of the 2006 data, appears to be stable today. The team believes that the counter-clockwise swirling will come back again at some point. Several computer models show it coming back with a much more profound impact on climate than was seen previously.
The team is continuing to gather and analyze sample data. While the trend they're seeing now is a restoration to previous bottom level pressures, salinity and temperatures, the Arctic Oscillation cycle will continue. Scientists will be observing these trends with new tools, satellites, and with greater computer processing potential as faster and faster machines come out to more accurately simulate something as large as the ocean.