How much atmospheric CO2 can we live with?

That’s the question James Hansen, director of the NASA-Goddard Institute for Space Studies, addressed on October 7 at the Joint Annual Meeting of the Geological Society of America, in Houston, Texas.

His short answer is less than 350 parts per million—the level Hansen believes will preserve Earth’s ice sheets, mountain glaciers, and head off a devastating sea-level rise.

The fact that we have now surged past 387 parts per million of CO2, with no effective control in sight, is alarming. 

A state of emergency

“I believe we’ve reached a state of emergency,” Hansen said, “although it’s not easy to see. But if you look at the science, it becomes clearer and clearer.”

It’s enough of an emergency to force him to rethink nuclear power, an issue on which he’s previously been “an agnostic.” Renewable energy alone in sufficient quantities, he said, would be too costly.

 

Hansen walked the audience through the science—ice cores that reveal CO2 levels over the past 800,000 years, microscopic shells from under the sea floor that track ocean bottom temperature and salinity for the past 35,000,000 years, reconstructions of past glaciations and sea levels, the current rates at which the Earth is warming and its ice sheets disintegrating, and computer models of the climate system.

The bottom line is that the amount of CO2 in the atmosphere drives Earth’s climate, and that we are driving CO2 off the charts.

“All we have to do is graph the greenhouse gas forcing over the past several hundred thousand years,” says Hansen. “When we choose the right scale, it’s a hand and glove fit. Humans are now completely in charge of the composition of the atmosphere. CO2 and methane are far outside the range they’ve been in for millions of years.”

We’re in charge but out of control

Did you catch that—“Humans are now completely in charge of the composition of the atmosphere.” In charge, but out of control, like airplane without a pilot.

We’re not even close to heading in the right direction. Even countries that signed on to the Kyoto Accord have increased their carbon emissions. There’s more CO2 in the atmosphere than at any time in the last 650,000 years, and the rate at which it’s increasing is itself increasing.

“The actual actions of countries worldwide are inconsistent with stopping the CO2 rise,” Hansen said. “Energy departments around the world are assuming we can burn all the remaining fossil fuel. That will double or triple atmospheric CO2.”

What that means, he said, is that unless global carbon emissions are cut drastically, and soon, we’re headed for “. . . a completely different planet than the one that’s existed in the past. Obviously, it would be an ice-free planet, warmer than it’s been in any of the recent interglacials.” 

Among other impacts Hansen foresees is the disappearance of glaciers in the Himalayas, Rockies, and Andes within the next few decades, threatening the water and food supplies of hundreds of millions of people. 

Hmm. Where would they go, and what kinds of upheavals would that kind of mass migration cause?

Irreversible tipping points

Hansen also warned about climatic and environmental tipping points, “where the dynamics of the system take over and you don’t need any more forcing and there’s the potential to lose control.”

One example is the disintegration of the ice sheets. “It takes thousands of years to build up an ice sheet from snowfall,” he said. “If we cause the West Antarctic ice sheet to disintegrate, that’s essentially irreversible.”

“I think that the metric for what is dangerous should be headed by these irreversible effects, such as the extermination of species,” he said. “We know that when there have been warmings of several degrees in the past, more than half of the species on Earth at that time went extinct.”

Remarkably, Hansen remains optimistic about our ability to push CO2 levels back below 350 parts per million and turn this looming catastrophe around. The keys are technology and public policy.

One necessary ingredient, he says, is to cut back immediately on the burning of coal as well as other fossil fuels. “We could say that we’ll only use coal at power plants where we will capture and sequester it,” he said.

Hansen also wants to see carbon emissions taxed. “The public has to understand that we have to put a price, a tax, on carbon emissions,” he said. “That has to be given back, so the person who reduces his carbon emissions more than average will make money.”

Hansen is now re-examining nuclear power. In principle, he says, fourth generation reactors can burn nuclear fuel far more efficiently than in the past, while generating much less--and less dangerous--waste.

“I think we should be doing the research on nuclear power and having a trial of fourth generation technology, because that may very well be necessary,” he said.

Crimes against humanity and nature

From Hansen’s point of view, business-as-usual versus re-stabilizing the climate is an intergenerational conflict with enormous moral and legal implications.

“It’s an inequity and an injustice for the young and the unborn,” he said. I think it raises ethical and legal questions about liability. There has been intentional misinformation of the public, which makes the companies that engage in that and fund the contrarians to misinform the public ethically and I think legally liable for what I call crimes against humanity and nature.”

Hansen does not believe that the free market alone can or will solve this problem. “The profit motive seems to be so strong that I don’t think we can rely on their conscience to change things,” he said. “We have to rely on public policy.”

Hansen has consistently and courageously advocated on behalf of a stable climate and a viable future for our children. We need to make sure our leaders know he's not alone, and that this may be our last chance to act.