Tuesday, July 15, 2008

More Snowball Earth

In case you didn't notice (most people didn't), last Friday the U.S. EPA came out with their Advance Notice of Proposed Rulemaking concerning the regulation of greenhouse gases to combat global warming. Not that the Bush Administration was anxious to roll this out, but their hand was forced by the recent Supreme Court ruling in Massachusetts v. EPA.

In April 2007, the Supreme Court concluded that greenhouse gases meet the definition of an "air pollutant" found in the Clean Air Act. Therefore, they ruled, EPA has the authority under the Act to regulate greenhouse gases, subject to a determination that the emissions from new motor vehicles cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare. A decision to regulate emissions for motor vehicles will also help determine whether other sources of greenhouse gas emissions need to be regulated as well, including stationary sources of air pollutants (e.g., power plants).

This is a complex issue. The science of climate change is complex. The reason that I posted about the Snowball Earth theory last week was that, somewhat counter-intuitively, it was Snowball Earth theory that led me to an understanding, if partial, of the complexities of greenhouse global warming.

Looking back over geologic time, it is apparent that the Earth has gone through several climate extremes, from pole-to-pole glaciation with the entire planet covered by ice (Snowball Earth) to extreme greenhouse conditions with no arctic ice at all and sea levels thousands of feet higher than present (Greenhouse Earth). The reason for these dramatically different conditions has lessons for us concerning the current climate change crisis.

Snowball Earth conditions begin when small, naturally occurring variations in the Earth's orbit create a few successive years of abnormally cold winter. More ice develops at the poles and more snow remains on the mountains. The reflectivity (albedo) of all this ice and snow bounces more of the thermal energy from the sun back into space, rather than using the energy to heat the Earth. As a result, conditions get colder still, which generates more ice and snow, which reflects still more thermal energy away. This feedback effect creates a colder and colder climate, until continental glaciers take over the land mass, the oceans freeze and the entire globe is encased in ice. This apparently happened about 635 million to 700 million years ago during the Late Precambrian, and maybe other times as well.

But once Snowball Earth conditions begin, how do they end? Why aren't we in a permanent Snowball condition, continually reflecting the sun's warmth away? Geologists speculate that eventually, a volcano breaks through the glacial ice somewhere on the planet and starts spewing carbon dioxide and methane into the atmosphere. This will cause local warming conditions, which melts some of the ice away and allows the Earth to receive the thermal energy from the sun. This warm spot, in turn, starts to melt away more of the ice, uncovering more and more darker ground to receive solar warmth. During the warming period, other factors also contribute to the rise in carbon dioxide and other greenhouse gases, including weathering of rock following deglaciation and algal blooms in the ocean. Soon, as more and more of the Earth is "defrosted," a reverse feedback begins, and the whole planet warms up and sheds its icepack.

The kicker is this - if one volcano emitting CO2 and methane can trigger a complex mechanism that eventually melts an entire ice-coated planet, what mechanisms are we triggering now with our global man-made releases of CO2? Once the equilibrium of the atmospheric chemistry is altered, it's not just the warming effect of the greenhouse gases themselves that will be our undoing, but the associated disruptions of oceanic currents, loss of the current arctic and alpine albedo, and so on.

Ever the optimist, I am still hopeful that we can find the political will to start directly addressing this issue, to regulate and control our emissions. It is, I'm afraid, too late to prevent the warming feedback mechanisms from starting and we will experience (are experiencing) some level of climate change, but it may not be too late to prevent triggering a full-blown Greenhouse Earth episode.

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