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Bridging climate science, citizens, and policy

Three Factors Contributed To Natural Global Warming 14,500 Years Ago

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A paper in the July 17th issue of Science presents results identifying three factors that contributed to the last major period of natural global warming:

  • an increase of about 40 parts per million in atmospheric carbon dioxide
  • a strengthening of the Atlantic Ocean’s conveyor belt circulation
  • the release of heat stored in the ocean over thousands of years

Identified as the Bølling-Allerød period, about 14,500 years ago, it was a period of time when the climate system warmed suddenly (in climatological terms) and strongly.  Critical steps along the way began with glacial melt.  Once that stopped, the enormous subsurface heat that had accumulated for 3,000 years erupted like a volcano and popped out over decades.  This huge heat flux melted the sea ice in the Arctic and warmed up Greenland.  In terms that most of us can understand, global sea level rose by 16 feet and temperatures in Greenland soared by up to 27 degrees Fahrenheit over several hundred years.  This points out that global warming events can occur quite rapidly and have devastating effects on the entire globe.

The findings were identified using simulations, which were conducted on the Community Climate System Model (CCSM), which is a collaborative effort based at NCAR.

What’s similar in today’s world?  Well, the CO2 increase for starters.  We’re increasing the CO2 concentrations in the atmosphere by 40 parts per million every 20 years – for the past 120 years.  Today’s concentration is ~385ppm, whereas the average in the past 1000 years has been ~280ppm.  The IPCC considered cases where CO2 concentrations by 2100 would range from 500ppm to 1000ppm.  Even with aggressive action to reduce CO2 emissions, concentrations will rise for the remainder of this century.  What will that do?  How is that condition related to the other two factors that contributed to the last period of major global warming?

The oceans are undergoing expansion due to the addition of thermal energy.  How long will the oceans be able to take up excess heat before re-releasing it into the atmosphere?  That an important question that nobody has an answer to today.

Will the Atlantic Ocean’s conveyor belt circulation strengthen?  Or will we only face 2 out of 3 of the factors?  These are all important questions that we shouldn’t be toying with in order to protect immoral corporate profits.  I am not overstating the state of things when I say the fate of today’s societies and ecosystems hang in the balance.

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