Dan Kulpinski

NASA scientist James Hansen issued an urgent warning in his speech at the National Press Club in Washington, D.C., June 23.

The occasion was the 20th anniversary of his landmark 1988 testimony before a Senate panel, in which he warned that global warming was here and we were causing most of it.

Now he’s being just as forceful, but the outlook is worse. “We really are in a planetary emergency,” Hansen said. Greenhouse gas emissions (mostly carbon dioxide) have continued basically unabated since 1988, he noted, and atmospheric levels are now at 385 ppm (parts per million) — and we’re adding 2 ppm per year. At 450 ppm there would be no ice left on the planet, which would mean major changes in climate and sea level. At the world’s current rate of emissions, we could hit that point 33 years from now.

Hansen, who is the director of NASA’s Goddard Institute for Space Studies in New York City, said with greater than 99.9 percent confidence that the dangerous level is 350 ppm, so we have to cut our carbon emissions very soon. “We can overshoot a bit, but not on a timescale more than decades,” he said.

One issue with various international discussions and agreements on global warming, he said, is that nobody has defined what “dangerous” is. Hansen defines as “dangerous” consequences that are irreversible — the possible extinction of plant and animal species, the ice sheets on Greenland and Antarctica melting (and the subsequent sea level rise). These are not reversible on any timescale relevant to humans, he said, pointing out that yes, species have gone extinct before and new species appeared — but it takes hundreds of thousands of years for those new species to come on the scene.

One “tipping level” that we’ve already passed is the existence of Arctic sea ice. “Over the next five to ten years we are certainly going to lose it all,” he said. But this, he says, is reversible.

He noted that ice mass on Greenland is happening more and more rapidly (which we measure with the Gravity satellite), and that West Antarctica is also losing ice at an increasing rate.

Then he recited a list of familiar global-warming impacts: The subtropics have expanded toward the poles, making the southern U.S. more dry; glaciers are receding worldwide; warmer ocean temperatures and acidified waters are stressing coral reefs.

“The only way we can prevent going to an extremely different planet,” he said, is to stop burning coal in power plants that don’t capture the carbon emissions. He wants such uncaptured coal phased out by 2030 and also promotes a carbon tax, to put a price on emissions.

“Eventually we have to go to carbon-free energy,” he said.

One way he proposed to get there is to build a low-loss electric grid. He said we have the technology to build a high-energy, direct current grid and we could put it underground. We could have the trunk lines in within one decade, he feels. (U.S. electricity transmission and distribution losses were 7.5 percent in 1995, according to Wikipedia.)

During the question session afterward, he pointed out that the 2 ppm we add per year is 10,000 times what nature contributes each year in the carbon cycle. “We’re clearly in the driver’s seat.”

(You can find a PDF or Powerpoint of Hansen’s presentation here.)
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Later in the day, Hansen testified on Capitol Hill before a House committee. Check out the Associated Press coverage here.