A new report from the United Nation's panel of climate scientists offers little in the way of surprises: Climate change, it says, is almost entirely man-made; it will be irreversible if nothing is done soon; and reducing greenhouse gases to zero this century may be necessary to reverse its effects. This isn't surprising. The Intergovernmental Panel on Climate Change's final volume, dubbed the "Synthesis Report," echoes the previous three reports that relied on the findings of more than 800 scientists released over the previous 13 months.
"Science has spoken," U.N. Secretary-General Ban Ki-moon declared at the launch of the report in Copenhagen. "There is no ambiguity in their message. Leaders must act. Time is not on our side."
The report makes it clear that scientists are more certain than ever before that human activity is responsible for climate change. "Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history," the report says. To keep the the global temperature rise from reaching what the panel views as a dangerous level, emissions from fossil fuels may need to drop to zero by the end of the century. The report cites increasingly frequent and severe heat waves, melting glaciers, and dramatically changing sea levels as indicators of the accelerating rate of climate change.