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Good, bad, indifferent GW impacts … when did they begin?

December 18th, 2008 · No Comments

Anyone who suggests that Global Warming is a straightforward issue is either selling you a bill a goods or doesn’t know what they’re talking about. (They don’t know what they don’t know.) While, it is clear that current, rapid shifts to the atmosphere are drving change that, writ large, will be catastrophic without major shifts in our polluting and land-management patterns, one of the complexities is the dating of significant human impact on the climate and what the implications of that impact might represent.

The other day, several University of Wisonsin scientists (climatologist Stephen Vavrus, John Kutzbach, Gwenaëlle Philippon) presented a paper at the American Geophysical Union that “provided detailed evidence in support of a controversial idea” that human impacts began, in a globally noticeably way, millenia ago and might, in fact, have “prevent[ed] the world from entering into a new glacial age”.

A couple quick notes before exploring this further. (1) This is not an arena of expertise and I’ve not had a chance to read this material in detail. (2) To place a footnote of items into perspective, a point to highlight: amid the complexity, while perhaps a ‘little’ warming (or avoided cooling) accumulating over 1000s of years might represent a good thing, far more extensive warming occuring over decades (or even years) is a far riskier (and disastrous) path to follow.

And, to be absolutely clear, Vavrus is not a climate denier / skeptic:

“My views are very similar to those expressed by IPCC,” said Steve Vavrus, an associate scientist at the UW-Madison Center for Climatic Research.

This study looks at humanity’s agricultural impacts, based through ice core examination, and supports the hypothesis (”the radical idea”)

that human-induced climate change began not 200 years ago, but thousands of years ago with the onset of large-scale agriculture in Asia and extensive deforestation in Europe.

The study (the “computer simulations”) argues that

the cumulative effect of thousands of years of human influence on climate is preventing the world from entering a new glacial age, altering a clockwork rhythm of periodic cooling of the planet that extends back more than a million years.

Now, of course, before the “skeptic” community jumps on this as “proof” that Global Warming is an unadulterated good, putting aside the difference of a minor impact over thousands of years as opposed to major impact in tens, let’s hope that they spend time calling the modeling and simulation wrong so as to be consistent. Yeah, right …

This work seems to support the hypothesis

that the introduction of large-scale rice agriculture in Asia, coupled with extensive deforestation in Europe began to alter world climate by pumping significant amounts of greenhouse gases — methane from terraced rice paddies and carbon dioxide from burning forests — into the atmosphere. In turn, a warmer atmosphere heated the oceans making them much less efficient storehouses of carbon dioxide and reinforcing global warming.

On its face, it seems reasonable that human activity could have had planetary, and not just local, impact millenia ago. These researchers have used ice core measurements and state that they show an up-tick in both methane and carbon-dioxide beginning “between 5000 and 8000 years ago” that is “unlike during previous interglacial periods” when those greenhouse gases trended downward, not upward.

But, to reinforce, again, there is the differentiation between long-term, gradual, relatively low impact (enabling evolution and, perhaps, impeding radical change (ice age)) and fast / major impact through mass burning of fossil fuels.

“No one disputes the large rate of increase in greenhouse gases with the Industrial Revolution,” Kutzbach notes. “The large-scale burning of coal for industry has swamped everything else” in the record.

Tags: Energy · Global Warming · climate change · environmental