ONE TOWN SQUARE: at the intersection of peak oil, climate change, and land use

Bill McKibben in an article in The Washington Post says that perhaps the most crucial development in the two decade fight against global happened at the American Geophysical Union conference in San Francisco, and went largely unnoticed. NASA scientist James Hansen offered a simple, straightforward and mind-blowing bottom line for the planet: 350, as in parts per million carbon dioxide in the atmosphere.

“It’s a number that may make what happened in Washington and Bali seem quaint and nearly irrelevant.“

Twenty years ago, Hansen kicked off the climate change issue by testifying before Congress that the planet was warming and that people were the cause. Not really knowing what level of atmospheric CO2 might be dangerous, scientists speculated on what would happen if the pre-industrial 275 ppm doubled. 550 was a crude and mythical red line. As our knowledge increased, scientists became convinced that 450 parts per million was a more prudent target.

But the data just keeps getting worse. The news this fall that Arctic sea ice was melting at an off-the-charts pace and data from Greenland suggesting that its giant ice sheet was starting to slide into the ocean make even 450 look too high. We’re already at 383 parts per million, and it’s knocking the planet off kilter in substantial ways.

Hansen says it means we’ve already gone too far:

“The evidence indicates we’ve aimed too high – that the safe upper limit for atmospheric CO2 is no more than 350 ppm.”

The last time the Earth warmed two or three degrees Celsius – which is what 450 parts per million implies – sea levels rose by tens of meters, something that would shake the foundations of the human enterprise should it happen again. And we’re already way past 350, and climbing inexorably.

Does that mean we’re doomed? Hansen thinks not necessarily. The Earth naturally gets rid of some of its CO2 each year. We just need to stop putting more in and, over time, the number will fall, perhaps fast enough to avert the worst damage.

The difference between 550 and 350 means that we have before us the biggest political and economic task we’ve ever faced: weaning ourselves from coal, gas and oil, now and everywhere. The gentle measures bandied about at Bali, themselves way too much for the Bush administration, don’t come close.

Hansen called for an immediate ban on new coal-fired power plants that don’t capture carbon, the phaseout of old coal-fired generators, and a tax on carbon high enough to make sure that we leave tar sands and oil shale in the ground.

Joseph Romm takes issue with Hansen and McKibben – not because he thinks they’re wrong:

“Exactly when those feedbacks seriously kick in is the rub. No one knows for sure, but based on my review of the literature and interviews of leading climate scientists, somewhere between 400 and 500 ppm seems most likely. It could be lower, but it probably couldn’t be much higher.”

but because he thinks the consequences of their being right are unacceptable:

“If 350 ppm is needed (and I’m not at all sure it is) then the deniers and delayers have won, since such a target is hopeless.”

Romm argues that we simply cannot cut carbon emissions deeply enough or quickly enough to hit a 350 ppm target:

“Humanity cannot, however, cut its hydrocarbon diet 80% tomorrow or even, realistically, in 10 years. That would require replacing the world’s entire energy infrastructure — power plants, cars, planes, factories, fueling infrastructure, large parts of homes and commercial buildings — while simultaneously deploying a hydrocarbon-free energy system in the rapidly-growing developing world. cut its hydrocarbon diet 80% tomorrow or even, realistically, in 10 years. That would require replacing the world’s entire energy infrastructure – power plants, cars, planes, factories, fueling infrastructure, large parts of homes and commercial buildings – while simultaneously deploying a hydrocarbon-free energy system in the rapidly-growing developing world.”

Romm may be pointing out what truly is an inconvenient truth. But it’s not relevant to the science of whether 320, 350, or 450 ppm will lead to catastrophic climate consequences.