January 05, 2008

Feedback Effects

A couple of recent stories show how the changing climate is producing more change more rapidly and, indeed, the feedback from these changes drives even more change.

In December, NPR's Climate Connections had a story about the melting glaciers high in the Himalayan mountains. One glacier currently feeding four major rivers in China is melting much faster than anyone ever predicted.

"When we first started observing this glacier, it was retreating at about 80 feet per year, and now it looks like it's doubled," he says.

To explain the change, he cites an increase in temperatures.

"We've seen just in this area about a 2.2 degree increase in temperature just in the last 20 years. And it's interesting because it seems like, from the climate data that we've been studying, that this region is warming faster than some of the other parts of China. In fact, from the data that we have, this particular region is warming almost twice as fast as China," he says.

And why is this high mountain experiencing more warming than the rest of China? Because the mountain glaciers had once reflected the heat back to the sky and now enough snow has melted that they are soaking in the heat. It's the albedo effect.

The other story comes from this week's Living on Earth where Steve Curran interviews Jeremy Fisher who has been studying the carbon footprint of the decaying forests on the Gulf Coast hit by Hurricane Katrina. The amount of carbon dioxide released by the decaying trees is approximately 50-140% of the carbon dioxide the US forests are capable of consuming annually.

FISHER: In 320 million trees there's about 400 million tons of carbon. By our estimation, that's about the same amount that the entire U.S. is able to draw down in photosynthesis every year.

...CURWOOD: Now, we know that forests help make weather. I mean, aside from sequestering carbon in their leaves and such, they are part of the whole water cycle. So, how might the weather have changed in this area where all these trees were lost from Katrina? And how might that then affect the ability of the forests to regenerate itself?

FISHER: There are some studies which have indicated that when forests are lost in general it changes the microclimate of a region such that it starts to experience droughts. I would expect that this area has been hit often enough by hurricanes that at least the natural ecosystems are able to bounce back on a fairly regular basis and that should not be as much of a problem, except for the invasive species that we were referring to earlier.

In general, this whole cycle of hurricane hitting forests and flattening trees, which release carbon, sets up a potential positive feedback cycle, in which carbon dioxide is released from those trees, goes into the atmosphere, will make global warming just a little bit worse, which we anticipate will increase the number of hurricanes, which then flatten more trees, releasing more carbon, and that causes a positive feedback cycle.

CURWOOD: To what extent do you think we're in that cycle?

FISHER: It's hard to know. We're certainly heading towards that direction with the state of emissions where they are right now. The current climate models do anticipate that we are going to increase the number of hurricanes.

These are just two of the feedback cycles that come from our warming earth and yet we humans have more than tripled our contribution to this cycle since 2000.

Posted by Mary at January 5, 2008 02:43 PM | Environment | Technorati links |
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