March 24, 2015
Editor’s Note: Climate Central is an independent organization of leading scientists and journalists researching and reporting the facts about our changing climate and its impact on the American public. Its scientists publish and journalists report on climate science, energy, sea level rise, wildfires, drought, and related topics. This post appeared on Climate Central, March 23, 2015. More on John Upton at the conclusion.
A sweeping ocean conveyor system that ushers warm tropical waters into the North Atlantic appears to have partly recovered from a near-collapse around the time that the Beatles were breaking up, but the system remains weaker than it had been since before humans figured out how to write modern music on a page.
Powerful Atlantic Ocean currents fuel Gulf streams, affect sea levels, warm cities in continental Europe and North America, and bring nutrients up from ocean depths that help sustain marine ecosystems and fisheries.
But an avalanche of cold water from the melting Greenland ice sheet appears to be slowing the ocean circulation to levels not experienced in more than 1,000 years.
That’s the conclusion of a bold new attempt to combine temperature measurements and climate-related data scrounged from coral samples, ice cores and tree rings to track the worrying decline of the critical Atlantic Ocean phenomenon. The new research, published Monday in Nature Climate Change, used observations and studies of sea-surface temperatures to produce a new index — one that charts the waning force of the Atlantic meridional overturning circulation (AMOC), one of the planet’s most important circulation systems.
The index reveals a modern powering down of the AMOC, including a sharp slowdown between 1970 and 1990, which had already been widely detected, followed by a partial recovery that nonetheless failed to boost the system back to its vigorous pre-Industrial Revolution state.
If the climate relationships identified by the researchers, led by the Potsdam Institute for Climate Impact Research in Germany, hold true, growing melt rates in Greenland “might lead to further weakening of the AMOC within a decade or two, and possibly even more permanent shutdown” of key components of it, the scientists warn in their paper.