James E. Hansen, the climate scientist who issued the clearest warning of the 20th century about the dangers of global warming, will retire from NASA this week, giving himself more freedom to pursue political and legal efforts to limit greenhouse gases
His departure, after a 46-year career at the space agency’s Goddard Institute for Space Studies in Manhattan, will deprive federally sponsored climate research of its best-known public figure.
At the same time, retirement will allow Dr. Hansen to press his cause in court. He plans to take a more active role in lawsuits challenging the federal and state governments over their failure to limit emissions, for instance, as well as in fighting the development in Canada of a particularly dirty form of oil extracted from tar sands.
“As a government employee, you can’t testify against the government,” he said in an interview.
Dr. Hansen had already become an activist in recent years, taking vacation time from NASA to appear at climate protests and allowing himself to be arrested or cited a half-dozen times.
But those activities, going well beyond the usual role of government scientists, had raised eyebrows at NASA headquarters in Washington. “It was becoming clear that there were people in NASA who would be much happier if the ‘sideshow’ would exit,” Dr. Hansen said in an e-mail.
At 72, he said, he feels a moral obligation to step up his activism in his remaining years.
Anyone who doubts the reality of global climate change on earth is a total buffoon.
Just because Earth was warmer and life survived, does not mean that global warmiing is fine and dandy. No, the seas won't boil, but rising sea levels will flood hundreds of millions of peoples' homes. Would you like to go through the plague? Life survived it.
Jim Hansen lost his mind years ago . There is no fixed limit . In a billion years the Oceans will evaporate because the Sun is turning a Red Giant .
National Geographic Reports
Respected as Hansen is, the argument hasn't convinced climate scientists who specialize in the evolution of planetary atmospheres. During the Paleocene-Eocene Thermal Maximum (PETM), 56 million years ago, a huge natural spike in CO2 sent temperatures on Earth soaring―but life went on and the ocean remained intact.
"I think you can say we're still safe against the Venus syndrome," says Raymond Pierrehumbert of the University of Chicago. "If we were going to run away, we'd probably have done it during the PETM."
In his book Storms of my Grandchildren, noted climate scientist James Hansen issued the following warning: "[I]f we burn all reserves of oil, gas, and coal, there is a substantial chance we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty."
Venus has a thick atmosphere that is 96.5 percent carbon dioxide, which keeps its surface at nearly 900°F (482°C). The planet's water boiled off to space long ago. Could that really happen on Earth, which is farther from the sun, and where the CO2 level is just now rising past 400 parts per million?
The key to the argument is a well-documented positive feedback loop. As carbon dioxide warms the planet through the greenhouse effect, more water evaporates from the ocean―which amplifies the warming, because water vapor is a greenhouse gas too. That positive feedback is happening now. Hansen argues that fossil-fuel burning could cause the process to run out of control, vaporizing the entire ocean and sterilizing the planet.
Respected as Hansen is, the argument hasn't convinced climate scientists who specialize in the evolution of planetary atmospheres. During the Paleocene-Eocene Thermal Maximum (PETM), 56 million years ago, a huge natural spike in CO2 sent temperatures on Earth soaring―but life went on and the ocean remained intact.
"I think you can say we're still safe against the Venus syndrome," says Raymond Pierrehumbert of the University of Chicago. "If we were going to run away, we'd probably have done it during the PETM."
In the past few years, however, physicists have been training supercomputers on the lowly water molecule, calculating its properties from first principles―and finding that it absorbs more radiation at more wavelengths than they'd realized before. In a paper published this week in Nature Geosciences, those calculations have rippled into a simple climate model. The paper's conclusion contains this slightly unsettling sentence: "The runaway greenhouse may be much easier to initiate than previously thought."
National Geographic asked the lead author, Colin Goldblatt of the University of Victoria in British Columbia, to explain.
In an earlier paper, published just last year, you wrote that "it is unlikely to be possible, even in principle, to trigger a runaway greenhouse."
Yeah―and I was wrong! I was plain wrong then.
What do you say now?
It used to be thought that a runaway greenhouse was not theoretically possible for Earth with its present amount of sunlight. We've shown that, to the contrary, it is theoretically possible. That doesn't mean it's going to happen―but it's theoretically possible.
What changed?
The models we had were underestimating the amount of radiation that would be absorbed in a water-vapor-rich atmosphere.
How does that connect to the runaway greenhouse?
Going back to absolute basics―the surface of the Earth emits radiation, and some of that radiation gets absorbed in the atmosphere by gases like CO2 and water vapor. This means less radiation can get out to space than if there were no greenhouse atmosphere. Or conversely, to get the same amount of radiation out to space to balance the energy you're getting from the sun, the surface needs to be hotter. That's what's happening now: Because we're making the greenhouse effect stronger, the Earth is heating up so it will come back into balance.
Now, if you put enough water vapor in the atmosphere, any radiation from the surface will get absorbed before it gets out to space―all of it, everything. Only the upper part of the atmosphere can emit radiation to space. So it turns out there's a fixed amount of radiation you can emit to space once you have enough water vapor.
It's like if you take a layer of tinted glass―one layer, you'll be able to see through. But if you stack up 10, 20, or 100 layers, you can't see through it.
So the runaway greenhouse effect happens when the amount of incoming solar radiation exceeds this fixed limit?
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