A 60-Year Glimpse At Local Climate Change Effects

Three things you need to know:

—Plants and animals around the world are changing their behavior and their distributions in response to global warming.

—Multiple factors affect local climate, including elevation, how land is used and the distance to a major source of water.

—Current global climate models do not simulate climate changes at local scales well, so other methods are needed to help make such projections more accurate.

Mt. Ashland Ski Area in the Siskiyou Mountians, photo by Michael McCullough/Flickr

The debrief:

Beginning in 1949, an ecologist named Robert Whittaker travelled the Siskiyou Mountains in southwestern Oregon for two years and collected a record of the different herb species throughout the area. His intention was to see how position on a mountain slope affected which plants grew. Now, 60 years later, Whittaker’s detailed data is helping scientists understand how plants are responding to climate changes at very fine scales. 

During the summers of 2007 and 2008, a group of researchers retraced Whittaker’s steps through the Siskiyou Mountains as they studied the populations of herbs. In the past 60 years, the entire area has experienced an average temperature rise of almost 5°F. But it turns out that plants in some areas have responded to this differently than plants in other areas, even within this small forest area of only a few thousand square miles.

For example, at low elevations, the researchers say, the plant communities have adapted to drier conditions compared to what Whittaker observed. Yet higher up the mountain slopes, and sometimes just a few miles away, the same response wasn't observed; in some cases, there was more leafy coverage in the forests than was recorded by Whittaker. The implication of this is that within a very short distance, very different responses to a warming climate were observed. In some areas, the plants growing there had ultimately changed or evolved. But just a short distance away, a similar plant population may have flourished.  

“One conclusion you could draw is that making climate change predictions at this scale is hard and chaotic,” says study co-author Ellen Damschen, from the University of Wisconsin, “but I think it shows [the changes] can actually be predictable.”

According to Damschen, the changes they observed make sense when you step back and think about what rising air temperatures can do; if an area of ground is already quite dry, warmer air can dry it out further. In areas higher up the mountain, hotter temperatures lead to earlier snowmelt and an overall longer growing season. 

These new findings are available online from the Proceedings of the National Academies of Science.

Why this science matters:

Scientists use computer models to predict climate changes on the global scale, which provide a broad outlook of how climate is changing. However, many of these models have difficulty providing reliable information at the local level, and the question of how ecosystems will respond to climate change is another uncertainty to grapple with. In order to glean information from a climate model about a smaller geographical region, scientists need to take their typical models a few steps further by incorporating additional information about air circulation and land use change at the regional and local levels. With this more detailed picture in hand, scientists can make a reasonable prediction of how climate change will affect specific places.

Still, the best way to detect what is going on at the hyper-local level is to go out and measure it, just like Harrison and her coworkers did in Oregon. In this recent example, the authors have learned, for example, exactly how the number and types of plants have changed in a specific area over the past 60 years. And they’ve observed differences between these changes when they compare land that is either higher up or lower down on the same mountain. It’s the kind of information that may soon be incorporated into a climate model that can more accurately predict changes at local scales.