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A Climate Fix? Not Too Cold, Not Too Hot, Just Right


by Bill Chameides | February 17th, 2009
posted by Erica Rowell (Editor)

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While some people have a hard time accepting the fact that humans are disrupting the climate, others conclude that not only are we changing the climate today, but have been for millennia. Now comes a bold (perhaps brash) proposal to use fossil fuels to tune the climate for the next 500,000 years.

More than likely, global climate disruption is not unique to industrialization, but actually began long ago when humans invented agriculture. There can be little doubt that the cutting down of forests for cropland changed the reflective properties of the Earth’s surface and thus somehow affected climate. For example, in a recent paper in Geophysical Research Letters Julia Pongratz of the Max Planck Institute of Meteorology in Hamburg, Germany and colleagues reported model simulations that showed significant regional warming from land-use changes as early as 800 A.D.

Even more intriguing is the so-called “Ruddiman Hypothesis” named for William Ruddiman, recently retired from the University of Virginia. I first came across Ruddiman’s ideas in his 2005 Scientific American article “Did Humans Stop an Ice Age,” but I gather a more comprehensive discussion can be found in his 2006 book entitled Plows, Plagues, and Petroleum: How Humans Took Control of Climate. (Full disclosure: I have not read the book.)

Ruddiman’s Hypothesis: Early Farming Practices Began Changing the Climate

Ruddiman’s hypothesis is that people began tinkering with the climate as much as 8,000 years ago. By chopping trees and irrigating fields, humans sent more carbon dioxide (CO2) and methane (CH4) up into the atmosphere than the amounts that natural cycles would have emitted. These extra greenhouse gas emissions, Ruddiman argues, were just just enough to stave off another ice age that by his reckoning should have occurred some 5,000 years ago. Of course even more warming occurred in the 20th century as human activities spurred by the industrial revolution caused even larger increases in CO2 and CH4 concentrations.

Things get even more interesting when Ruddiman looks to the future. In his vision, humans rapidly use up all fossil fuel reserves causing CO2 and global temperatures to rapidly spike, well above their present-day levels. Then CO2 slowly begins to decline, on time scales that we now understand to be of the order of a thousand years (see Susan Solomon’s recent paper), and global temperatures return to their “natural level.”

What happens next in Ruddiman’s hypothesis is uncertain. He concludes his Scientific American article like so: “Whether global climate will cool enough to produce the long-overdue glaciations or remain warm enough to avoid that fate is impossible to predict.”

Shaffer: Fossil Fuel Use Could Be Key to Tweaking the Climate

To this line of fascinating scientific speculation comes Gary Shaffer of the Niels Bohr Institute, University of Copenhagen. In a paper published last week in Geophysical Research Letters, Shaffer points out that our fossil fuel reserves are not just sources of energy. They represent a valuable potential resource for engineering – or tuning – the climate if we use them wisely. The first step in using them wisely in Shaffer’s scenario is to not use them up. Clearly if we follow the scenario envisioned by Ruddiman, all of the reserves are used up in short order, leaving none to help tune the climate.

By contrast, Shaffer posits a scenario in which society slows emissions rapidly – 20 percent reduction by 2020, 60 percent by 2050, and an exponential decrease to zero emissions thereafter. This scenario has two important results:

  1. Global temperatures peak at about 2 degrees Celsius above preindustrial times (instead of almost 5 degrees if fossil fuels are rapidly depleted); and
  2. Some 4,000 tons of the original 5,000-ton reserves of carbon in fossil fuels remain untapped.

Shaffer proposes that we can then use these untapped reserves to stave off ice ages. His calculations based on the Earth’s orbit around the sun suggest that without human intervention, the next ice age would befall us in some 50,000 to 170,000 years. Shaffer points out that if we use our remaining 4,000-ton reserve to spike CO2 concentrations at strategic times, we can delay the ice age’s arrival another 500,000 years.

These are interesting ideas. The notion that a global society of humans could come together and agree to use fossil fuels to regulate climate over the next hundreds of thousands of years seems a little utopian to me given the current state of the world.

In any event, the first step in Shaffer’s scenario is the same step we must take to avert dangerous climate change: namely, rein in global greenhouse gas emissions with an international agreement that helps convert the world’s economy to one characterized by low-carbon technologies. Is that too idealistic a notion? Hopefully not.

filed under: agriculture, carbon dioxide emissions, climate change, faculty, fossil fuels, global warming, methane
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