Greenhouse gases already take toll, panel says

WASHINGTON – The newest international assessment of the consequences of Earth’s warming climate has concluded with “high confidence” that human-generated greenhouse gases are already triggering changes in ecosystems on land and sea across the globe.

The second working group of the Intergovernmental Panel on Climate Change, which was charged with tracking the impact of global warming on specific regions and species, plans to release its final report in Brussels, Belgium. The Washington Post obtained a near-final draft of the report Wednesday.

That document – which follows on the heels of an earlier IPCC study in February that concluded with at least 90 percent certainty that humans are responsible for Earth’s recent warming – provides a more detailed look at how emissions from automobiles, industry and other sources are affecting life around the world.

The draft says “much more evidence has accumulated over the past five years” to indicate that changes such as longer growing seasons and earlier leaf-unfolding and earlier egg-laying by birds are traceable to human activities.

Thomas Lovejoy, an environmentalist who is president of the H. Heinz III Center for Science, Economics and the Environment in Washington, said the report amounts to “a sad confirmation of what I have been following for 20 years, namely that nature is very sensitive to climate change, more so than anything else, and that we are seeing responses – including threshold changes in ecosystems – in the living world all over the globe.”

The draft report makes distinctions between changes it considered significant with “high confidence” – at least 80 percent certainty – and those to which it assigned “very high confidence,” which means 90 percent certainty. While it says with “very high confidence” that earlier bird migrations and a shift of species toward the poles are results of warmer temperatures, for example, it said satellite data gave it only “high confidence” that “there has been a trend in many regions towards earlier greening of vegetation in the spring and increased net primary production linked to longer growing seasons and increasing atmospheric CO2 concentrations.”

Scientists from around the world contributed to the report, whose details were being finalized in Brussels this week. The authors relied on peer-reviewed scientific reports to make their findings, and the report was subjected to rounds of outside review.

In some cases the authors compared real-life observations with computer models of a warming world and found that they matched well, leading them to find “with high confidence” that the human-caused “component of warming over the last three decades has had a discernible influence on many physical and biological systems.”

The report also seeks to predict how warming could affect particular regions in the future, suggesting that drought-prone areas are likely to become drier and “extreme precipitation events, which are likely to increase in frequency and intensity, will augment flood risk.”

At the same time, the authors write, “water volumes stored in glaciers and snow cover are very likely to decline,” which will cut water supplies in parts of the globe “where more than one-sixth of the population currently live.”

Several scientists interviewed Wednesday said they had already begun to detect specific ways that climate change is altering ecosystems in the United States and abroad.

Camille Parmesan, a professor of integrative biology at the University of Texas at Austin, said several bird species, such as the Rufus hummingbird, have started residing year-round in Gulf Coast states rather than just migrating there part of the year from Mexico.

The new report estimates between 20 and 30 of the world’s species “are likely to be at high risk of irreversible extinction if global average temperature” rises between 2.4 and 4.5 degrees Fahrenheit.