Global Warming: Could Things Get Better Before They Get Worse?
April 13, 2012

Global Warming: Could Things Get Better Before They Get Worse?

Global warming could make things a little greener and a little rosier, according to new research. But these conditions may not last very long.

These new findings have been published in the journal Nature Climate Change this week. Within, evidence is shown that plants may experience a period of great growth and may initially thrive during global warming. Once this growth is over, however, plant life will begin to deteriorate quickly.

“We were really surprised by the pattern, where the initial boost in growth just went away,” said scientist Zhuoting Wu of Northern Arizona University (NAU), a lead author of the study.

“As ecosystems adjusted, the responses changed.”

To conduct this study, ecologists put four grassland ecosystems through simulated climate change for ten years. The ecologists noticed the plants began to grow quickly within the first year of simulated global warming. After this first year, however, plant growth progressively diminished, before disappearing in the ninth year,

In addition to showing decreased plant growth over a long span of time during global warming, the study also shows the effects of global warming on plant communities and how these plants manage their essential resources, such as nitrogen.

Saran Twombly, program director in the National Science Foundation (NSF)´s Division of Environmental Biology said in a recent press release: “The plants and animals around us repeatedly serve up surprises.”

“These results show that we miss these surprises because we don´t study natural communities over the right time scales. For plant communities in Arizona, it took researchers 10 years to find that responses of native plant communities to warmer temperatures were the opposite of those predicted.”

To simulate the effects of global warming, the team of ecologists transplanted their four ecosystems from higher to lower elevations. The change in the temperature also brought about a change in rainfall, subjecting the subject ecosystems to periods of greater or lesser precipitation.

The ecologists studied grasslands typically found in Northern Arizona that can stretch from the San Francisco Peaks to the Great Basin Desert.

According to their results, periods of long-term warming resulted in a loss of native species as well as an increase of species usually found in warmer climates, pushing the native species out.

As these grasslands warmed, they cycled through their nitrogen more quickly. Going into the study, the ecologists believed this kind of action would take place and leave more nitrogen available for the rest of the community. What they didn´t expect, however, was how much nitrogen would be lost. As the nitrogen was cycled through, it quickly converted to nitrogen gas in the atmosphere or was washed out by rainfall.

Senior author of the paper and lead ecologist at NAU Bruce Hungate said this loss of nitrogen is an important issue to note, as most researchers expect the increase of available nitrogen to sustain plant productivity.

“Faster nitrogen turnover stimulated nitrogen losses, likely reducing the effect of warming on plant growth,” Hungate said. “More generally, changes in species, changes in element cycles–these really make a difference. It´s classic systems ecology: the initial responses elicit knock-on effects, which here came back to bite the plants.”

“The long-term perspective is key,” said Hungate. “We were surprised, and I´m guessing there are more such surprises in store.”


Image Caption: Composite of the ecosystems studied, arranged left to right in order of increasing elevation. Credit: Paul Dijkstra and Michael Allwright