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A new U.N.-backed report by over 600 scientists from 40 countries says there now is at least 90% certainty that human activity is contributing to climate change.

In its Feb. 2 scientific assessment, its fourth, the Intergovernmental Panel on Climate Change forecasts continuing global warming, sea-level rises, erratic weather and widespread melting of ice and snow. IPCC was formed in 1989 by the World Meteorological Organization and the U.N. Development Programme. The panel has not previously asserted the human contribution to climate change with such a high degree of certainty.

The report “should compel all of us world leaders, businesses and individuals towards action,” says Martin Rees, president of the Royal Society, the U.K.’s national science academy. He had no part in the assessment.

IPCC says global temperatures could increase 6.4°C at worst or up to 4°C at best estimate, and sea levels could rise up to 59 centimeters. Regardless of any emissions reductions that are achieved in the future, “anthropogenic warming and sea-level rise would continue for centuries,” adds the report.

Concentrations of atmospheric carbon dioxide, “the most important anthropogenic greenhouse gas,” exceed “by far” the natural range over the last 650,000 years, says the report. Carbon dioxide levels rose from about 280 parts per million in the pre-industrial period to 379 ppm in 2005, says IPCC. Average growth in the last decade was 36% faster than over the previous 35 years. To stabilize atmospheric CO2 at 450 ppm, emissions would have to be cut by 27%, on average, over the century, says IPCC.

The report was published in summary following its review by about 620 experts and over 100 officials from governments at a Paris conference that began in March 2006. The full report is due out later this year.

special theme issue:
  1. Dire Global Warnings Inspire Promising Antidotes to 'Civilization'

  2. View a Time Line of Environmental Twists and Turns, from 1938 to 2007 (1.7MB)

  3. Report Lights Fires Globally on Need To Slow Climate Change

  4. Politicians, Builder Groups Jump on the Green-Building Bandwagon

  5. Climate Shifts Have Engineers Rethinking Baseline of Planning

  6. Designers Look To Nature To Render Buildings in Harmony with Earth

  7. Companies Often Go Green To Reap Financial Rewards

  8. Officials Begin To Ask Just How Green a Highway Can Be

  9. Educators Issue Call for Green Programs That Cross Disciplines

  10. Coming Carbon Constraints Spur Powerplant-Emission Cleanups

  11. Eco-Friendly Engine Pioneers Search for Sources of Clean Power

  12. Big Zero-Carbon Project Planned in U.K.

  13. Template for Green Cities Nears in Asia

  14. An Agitated Port Official Pushes for Collaboration

  15. Human Role in Climate Change Is 90% Certain

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  18. Barometer of Change at NOAA
  19. In Search of the Zero-Energy Holy Grail
  20. Green Building Council Hones Rating System