In 2006, the great climate scientist James Hansen famously said
I think we have a very brief window of opportunity to deal with climate change ... no longer than a decade, at the most.
Since then, things have gotten much, much worse. The Arctic ice is melting faster than expected. CO2 emissions are accelerating. Global warming is accelerating.
Hansen no longer stands by his estimate that we have one decade to turn things around. He now thinks that was too optimistic.
Today, James Hansen told congress that we have one year.
The transcript of Hansen's testimony can be found here (pdf). (Update: His slides can be found here (ppt) h/t A Siegel. Highly recommended.. these answer many of the excellent scientific questions in the comments better than I could.)
His thesis, basically, is that a stable climate requires atmospheric concentration of CO2 no more than 350 ppm. Unfortunately, its now around 385 ppm, and rising at 2 ppm/year. Currently, our policies-- written by the fossil fuel industry-- will likely keep CO2 rising for the forseeable future,leading to mass extinctions, as well as mega-droughts affecting hundreds of millions, and an impovershment of humanity. We still have time-- just barely to avoid most of this-- but we will need radical, transformative change in the next American administration.
(And lest anyone think that Hansen is just saying this to get a Democrat elected, don't forget that Hansen has clashed with Al Gore in the past.)
But enough of my summary. Go read the transcript of his testimony. Alternatively, because congressional testimony is part of the public record, I'm going to quote from it quite extensively (the emphasis is all mine.)
Again a wide gap has developed between what is understood about global warming by the relevant scientific community and what is known by policymakers and the public. Now, as then, frank assessment of scientific data yields conclusions that are shocking to the body politic. Now, as then, I can assert that these conclusions have a certainty exceeding 99 percent. The difference is that now we have used up all slack in the schedule for actions needed to defuse the global warming time bomb...
Otherwise it will become impractical to constrain atmospheric carbon dioxide, the greenhouse gas produced in burning fossil fuels, to a level that prevents the climate system from passing tipping points that lead to disastrous climate changes that spiral dynamically out of humanity's control...
I argue that a path yielding energy independence and a healthier environment is, barely, still possible. It requires a transformative change of direction in Washington in the next year...
Climate is nearing dangerous tipping points. Elements of a "perfect storm", a global cataclysm, are assembled... ominous tipping points loom. West Antarctic and Greenland ice sheets are vulnerable to even small additional warming. These two-mile-thick behemoths respond slowly at first, but if disintegration gets well underway it will become unstoppable. Debate among scientists is only about how much sea level would rise by a given date. In my opinion, if emissions follow a business-as-usual scenario, sea level rise of at least two meters is likely this century. Hundreds of millions of people would become refugees. No stable shoreline would be reestablished in any time frame that humanity can conceive...Other species attempt to migrate, but as some are extinguished their interdependencies can cause ecosystem collapse. Mass extinctions, of more than half the species on the planet, have occurred several times when the Earth warmed as much as expected if greenhouse gases continue to increase. Biodiversity recovered, but it required hundreds of thousands of years.
Arid subtropical climate zones are expanding poleward. Already an average expansion of about 250 miles has occurred, affecting the southern United States, the Mediterranean region, Australia and southern Africa. Forest fires and drying-up of lakes will increase further unless carbon dioxide growth is halted and reversed. Mountain glaciers are the source of fresh water for hundreds of millions of people. These glaciers are receding world-wide, in the Himalayas, Andes and Rocky Mountains. They will disappear, leaving their rivers as trickles in late summer and fall, unless the growth of carbon dioxide is reversed.
Coral reefs, the rainforest of the ocean, are home for one-third of the species in the sea. Coral reefs are under stress for several reasons, including warming of the ocean, but especially because of ocean acidification, a direct effect of added carbon dioxide. Ocean life dependent on carbonate shells and skeletons is threatened by dissolution as the ocean becomes more acid. Such phenomena, including the instability of Arctic sea ice and the great ice sheets at today's carbon dioxide amount, show that we have already gone too far. We must draw down atmospheric carbon dioxide to preserve the planet we know. A level of no more than 350 ppm is still feasible, with the help of reforestation and improved agricultural practices, but just barely– time is running out...
The public must send a message to Washington. Preserve our planet, creation, for our children and grandchildren.
Scientists are trained not to use language like this. They almost never do.
Unless they really mean it.
We have one year. One election.
And simply winning is not enough.. we will need radical changes in policy.
And if we lose...
Update: I want to respond to two points made in the comments.
- Some have said that prosecuting CEOs should be a key point, to dramatize the urgency of the situation. I respect this POV, but disagree. When you see a building burning in the middle of the night, the first thing you do is alert its occupants and the fire department. Prosecuting the arsonists can come later. Right now, IMO, the urgency of this emergency trumps all else.
- Some have speculated that we have already passed tipping points, and there is nothing we can do. The first may be right (probably is, unfortunately), but I strongly disagree with the second. a) Keep in mind there are widely varying degrees of badness: 1 million people dying is very different from ten million dying, which is very different from a billion dying, which is very different from 5 billion dying, which is very different from 6 billion dying. I don't know where on this scale we fall, but I think we still very much do have the ability to keep it close to the start. So b) all these windows are closing fast. That's why Hansen-- and so many of us here on dKos-- feel such a strong sense of urgency.