The world needs to completely phase out coal emissions over the next 20 years to avoid climate disaster, James Hansen, the head of NASA’s Goddard Institute of Space Studies (GISS) told a room packed with several hundred people at the AGU conference in San Francisco on Wednesday.

An immediate moratorium on new coal use that does not capture CO2 and phasing out of all other coal emissions by 2030 is the path to reach a target for CO2 emissions of 350 parts per million (ppm) identified in a new study led by Hansen. Previously, Hansen has said that the dangerous level for CO2 was likely to be 450 ppm or higher, but in light of new observations and analysis of ‘slow’ feedback processes like ice melt and greenhouse gas release from the ocean and soil, the study team revised that projection.

Unfortunately for the world, current atmospheric CO2 levels are already at 385 ppm.

(Hansen, a well-known climatologist, received a lot of publicity in 2005 and 2006 over his assertions that NASA administrators tried to censor his public statements about the causes of climate change.)

“We’ve got to get politicians to understand that it is more serious, and we’re at a more critical stage, than they seem to understand,” said the scientist. “No one is doing anything even close to what’s needed, even those countries who appear to be the most serious.”

Hansen’s colleague Pushker Kharecha acknowledged in an earlier lecture that phasing out coal over the next 20 years would be a “Herculean” task, but that it is possible, and necessary. Even if the world comes together to meet this goal, atmospheric CO2 would peak at 400-425ppm before gradually declining with the help of reforestation and other efforts.

Hansen warned that because of certain feedback loops, there will be no escape from “The Venus Syndrome” – runaway global warming – once the climate reaches certain tipping points. We may have already reached the tipping point with the Arctic sea ice which has decreased dramatically, he said. Other indicators he cited are a quadrupling of wildfires in American West over the last 30 years and the rapid retreat of glaciers, which he predicted will have disappeared within 50 years under a “business as usual” scenario.

All of this led one member of the audience to ask the question in everyone’s mind:

“Is the planet just doomed?”

To that Hansen replied that some human causes actually have slowed, such as CFCs and methane, and that there are technologies worth exploring like burning nuclear waste. Then he added, “I think we’ll solve the problem, but we need to tell the truth that it does require a carbon price. Politicians are not willing to do this.”

I can’t say I found his answer especially reassuring.