Reposted from NYTimes:
http://www.nytimes.com/2007/04/05/science/earth/05climate.html?ref=science

The latest United Nations assessment of the role of humans in global warming has found with "high confidence" that greenhouse gas emissions are at least partly responsible for a host of changes already under way, including longer growing seasons and shrinking glaciers.

A summary of the working draft of the report, to be released Friday in Brussels, was provided to The New York Times yesterday by several people involved in reviewing it. It is a detailed follow-up to a February report by the United Nations group, the Intergovernmental Panel on Climate Change, which was the fourth assessment since 1990 of the basic science that points to a human hand on the planet's thermostat.

That report said there was at least a 90 percent chance that most warming since 1950 had resulted from a continuing buildup of heat-trapping emissions in the atmosphere. The new report describes the specific effects of climate changes on people and ecology; identifies those species and regions at greatest risk; and describes options for limiting risks.

Some of the changes could be beneficial, but most will prove harmful in the long run, the report says.

It finds that global warming caused by humans has almost certainly contributed to recent shifts in ecosystems, weather patterns, oceans and icy regions, and that it will have large and lasting effects on human affairs and on the planet's web of life in this century.

The draft report predicts a variety of health effects as well, with "increased deaths, disease and injury due to heat waves, floods, storms, fires and droughts," but also "some benefits to health such as fewer deaths from cold."

Also in the plus column, higher concentrations of carbon dioxide, the main heat-trapping gas, are contributing to a greener world, according to the draft.

"Based on satellite observations since the early 1980s, there is 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," it said.

But warming in cool regions can bring mixed results, the draft says. For example, while temperate and higher latitudes could be friendlier to farming, they are also proving friendlier to weeds, as well as insect pests and wildfires that are likely to imperil forests.

Final details of the summary are being discussed by hundreds of authors and government representatives from more than 100 countries meeting this week in Brussels and conferring by e-mail.

Scientists and government officials sparred over the wording of the draft on Wednesday, according to some people involved, with disagreements on the level of certainty in projections of health and ecological consequences of warming.

But over all, the report is expected to provide significant new detail on a world increasingly influenced by human actions, most notably the buildup of carbon dioxide and other greenhouse gases emitted mainly by burning fossil fuels and forests.

In the long run, most regions are likely to be more harmed than helped by the changes, the draft says. For example, projections for coming decades foresee intensifying drought and downpours, as well as a relentless intrusion of rising seas — at an uncertain rate — along crowded coasts and around low-lying islands.

Water supplies fed by alpine snows or ice sheets are already experiencing changes and could be greatly disrupted, it said.

Among other findings, the draft says:

¶"Coasts are very likely to be exposed to increasing risks due to climate change and sea-level rise, and the effect will be exacerbated by increasing human-induced pressures on coastal areas."

¶"It is likely that corals will experience a major decline due to increased bleaching and mortality due to rising seawater temperatures."

¶Many of the world's regions that are already vulnerable to climate and coastal hazards are likely to see the biggest effects from additional changes driven by the buildup of greenhouse gases. "Poor communities can be especially vulnerable," it says, "because they tend to be concentrated in relatively high-risk areas, have more limited coping capacities, and can be more dependent on climate-sensitive resources such as local water and food supplies."

The existing and projected threats to these regions are justification for a greatly intensified effort by development groups, wealthy countries, and governments in poor countries to increase resilience in regions most at risk, officials said.

Achim Steiner, a United Nations under secretary general who is executive director of the United Nations Environment Program, would not comment directly on the climate panel's draft findings. But he said in an e-mail exchange that development projects in the world's struggling countries would need to take climate hazards into account.

"Trillions of dollars will be invested in infrastructure in developing countries alone over the coming years," he said. "The challenge is to ensure that climate change impacts are factored into investment decisions at the outset so that, say a road, railway or power plant, is planned with climate change in mind."