Monday, November 13, 2006

Double whammy: acceleration and feedback

The global warming naysayers always accuse the scientific community of exaggerating the dangers posed by global warming. In fact, the opposite is true. What the naysayers don’t get is that the scientific projections are, by their nature, almost always conservative. Why? Because they tend to extrapolate past history linearly into the future. What’s wrong with that? Two things: acceleration and feedback.

Acceleration: The problem with extrapolating past CO2 emissions trends into the future is that the increases aren’t linear – they’re accelerating. New data presented by the Global Carbon Project (a consortium of 200 scientists worldwide) at an Earth science conference in Beijing earlier this month shows that global carbon emissions are now growing at a 3.2% per year clip. The average rate of growth as recently as the 1990s was 0.8%. That means that our CO2 production rate has quadrupled from one decade to the next – and we’re only halfway through this one. That also means that we’re already way beyond the IPCC projections that the naysayers were throwing so much heat at in 2001.

It’s not just the carbon, either. Sea-level is now rising at a rate that’s at the upper end of the IPCC projections of just five years ago, and that rate is also accelerating.

In an earlier post (September 12th) I described a plan put forth by two scientists for solving the carbon problem using existing technologies. They based their plan on the fact that we were pumping 7 billons tons of carbon into the atmosphere a year. Now we’re pumping 9 billion tons a year into the atmosphere. That’s almost a 30% increase in just a few years.

Feedback: One feedback loop that has gotten a fair amount of press before occurs in the polar regions: as more ice melts, less sunlight is reflected back into space and therefore more is absorbed into the ocean, heating it up, which melts even more ice, which means more sunlight is absorbed into the ocean, and so on and so on. Because of this feedback loop, many scientists believe we may have already passed the point of no return on Arctic sea ice – and when it’s gone, we don’t know if it will ever come back.

A second worrisome feedback loop has come to light more recently: as the permafrost in the northern tundra melts, less sunlight is reflected back from these regions as well, meaning the ground absorbs more sunlight, heating it up, causing more permafrost to melt, and the spiral continues. The big problem here is that there is a HUGE amount of methane trapped under the permafrost, and as the permafrost melts that methane escapes into the atmosphere. Recent measurements in Russia indicate that the rate of methane emission is accelerating as well. Add to this the fact that methane is 20 times more potent that CO2 as a greenhouse gas, so releasing more methane heats up the atmosphere even faster, which means ice and permafrost will melt even faster, releasing methane at an accelerating rate… get the idea.

We’re just starting to get a handle on the nature and size of these feedback mechanisms – which means they aren’t represented in the climate models yet. Which means that the climate models, if anything, are underestimating the severity, and urgency, of the global warming problem.