Sunday, July 09, 2006

Global Warming

1. A recommendation to see the movie about Al Gore's slide show on global warming, An Inconvenient Truth.
How can a movie which is little more than a computer slideshow lecture be so engaging? It doesn't drag and the viewer is bound to be thinking about it days later. I think the answer is that the evidence he presents is truly compelling.
The photographic evidence of glaciers retreating in North America, South America, Europe, Asia, and Africa is only one of a litany of types of evidence that the climate is changing, that the change is at least in part due to human activities, and that the rate of change is accelerating.

Critics can only attack one of these conclusions: that the change is due to human activities. For the practical among us, it's academic to debate the exact degree of blame and where it falls when the bottom line is that coastlines will be changing and that people dependent on glacial melt for drinking water are getting thirsty. IF human actions can reverse or stabilize the trend, regardless of its cause, what are the reasons for not signing on?

One of the movie's points which is worth repeating is that there is a gap between everyday human-scale experience and the effects of global warming. Although there can never be evidence that a particular hurricane would not have occurred if car emission standards were stricter, it takes experiences that are personal to motivate belief and then action. Gore argues that the scale of the danger presented by global warming is outside the range of other catastrophic experiences that are tangible within a human lifetime. It is also out of scale (both geographically and temporally) with other natural/social problems which policies have been able to solve (e.g., the eradication of smallpox). This quality lends the problem unique urgency while also threatening to paralyze movement toward solutions.

This movie is headed for heavy classroom rotation, I predict. We can hope that it will also provide a model for how to give a good slide-based lecture: use slides for visual evidence, not as a substitute for lecturing skill and careful preparation.

2. A report in this week's Science about the association between wildfires in the western US and climate change:
Westerling, A.L. et al. Warming and earlier spring increases western U.S. forest wildfire activity. (8 July 2006).

The study has two parts: First, it documents an increase in wildfire activity in the western U.S. for the period 1987-2003 as compared with the period 1970-1986. 'Increase in activity' means a nearly fourfold increase in the frequency of large wildfires (fires > 400 ha) and greater than a sixfold increase in area of forest burned. The greatest increase was in the Northern Rockies at mid-elevations. The Southwest showed a similar trend on a relative size basis but the study region was smaller. Second, the authors examined the relationship between the increase in fire activity and regional changes in climate and hydrology. They found that the increase was associated with longer fire seasons, warmer spring temperatures, earlier spring snowmelt, and increased summer drought. These climate and hydrology factors were most pronounced in the Northern Rockies, precisely the area which has seen the most increased wildfire activity in the past two decades.

The study strongly suggests that climate changes which are of a piece with other effects of global warming are a significant cause of our largest and most severe wildfires. The mid-elevation Rocky Mountain areas most affected by an earlier and quicker spring snowmelt are also those areas which are typically covered by lodgepole pine and spruce-fir forests--forest types that are conducive to dramatic, explosive crown fires.

The burning issue here is that forests are carbon sinks and a significant hedge against further increases in the atmospheric carbon levels that are linked to climate change. In Alaska and northern Canada, warmer temperatures have been conducive to the spread of pests that attack and thin the boreal forests, reducing their ability to store carbon. This new study indicates that more temperate forests are likewise at risk of feeding an acceleration of global warming rather than shielding against it.

No comments: