Climate Change: Even Worse Than You Think

| Fri Sep. 25, 2009 12:11 AM EDT

Juliet Eilperin reports in the Washington Post:

Climate researchers now predict the planet will warm by 6.3 degrees Fahrenheit by the end of the century even if the world's leaders fulfill their most ambitious climate pledges, a much faster and broader scale of climate change than forecast just two years ago, according to a report released Thursday by the United Nations Environment Program.

That's odd.  This is 3.5 degrees Celsius.  A couple of hours ago that same story said 7.2 degrees Fahrenheit, or 4 degrees Celsius.  But if you click on the link and read the UN report, neither of those numbers appears.  At least, not that I can find.  What's going on?

Robert Corell, who chairs the Climate Action Initiative....collaborated with climate researchers at the Vermont-based Sustainability Institute, Massachusetts-based Ventana Systems and the Massachusetts Institute of Technology to do the analysis. The team has revised its estimates since the U.N. report went to press and has posted the most recent figures at ClimateInteractive.org.

The group took the upper-range targets of nearly 200 nations' climate policies — including U.S. cuts that would reduce domestic emissions 73 percent from 2005 levels by 2050, along with the European Union's pledge to reduce its emissions 80 percent from 1990 levels by 2050 — and found that even under that optimistic scenario, the average global temperature is likely to warm by 6.3 degrees.

Ah.  The number comes not from the UN report, but from Robert Corell.  And it's been updated, which presumably accounts for the Post story being updated.

Except that if you go to ClimateInteractive.org, their graph still says 4 degrees Celsius.  And it seems to be based on a model called C-ROADS, not the UN report.

So color me confused.  Except for one thing: both the UN report and Corell's analysis agree that climate change is much worse than we thought even a few years ago.  Virtually every measure of warming is increasing faster than our models predicted — something that regular readers of this blog already know.  From the first chapter of the UN study:

The climate forcing arriving sooner-than-expected includes faster sea-level rise, ocean acidification, melting of Arctic sea-ice cover, warming of polar land masses, freshening in ocean currents, and shifts in circulation patterns in the atmosphere and the oceans.

....In early 2008, a team of scientists published the first detailed investigation of vulnerable Earth System components that could contain tipping points. The team introduced the term ‘tipping element’ for these vulnerable systems and accepted a definition for tipping point as “...a critical threshold at which a tiny perturbation can qualitatively alter the state or development of a system...”

The nine tipping points are below.  Three of them could happen within ten years, and two more are possible within 50.  Time to quit mucking around, folks.

UPDATE: The ClimateInteractive folks now seem to have updated their graphs to show warming of 6.3°F/3.5°C.  Graphs are here.

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