Back in 2008, I wrote about whether ‘runaway’ climate change might be possible on Earth. At one point, Venus had liquid water on its surface. Then, the sun grew brighter and Venus warmed. Its oceans evaporated and huge amounts of carbon dioxide (CO2) got baked out of the crust. The heat made the water break up into hydrogen and oxygen: the oxygen bonded with carbon to make more CO2, and much of the hydrogen escaped into space. Venus became permanently hostile to life, with surface temperatures of 450°C.
Could burning all of Earth’s fossil fuels produce the same outcome?
Some people take comfort from the fact that there have been times in the history of the planet when greenhouse gas concentrations were much higher than now. The world was very different, but there was no runaway greenhouse and life endured. James Hansen devotes the entire tenth chapter of Storms of My Grandchildren to considering whether this assessment is valid. Three things give him pause:
- The sun is brighter now than it was during past periods with very high greenhouse gas concentrations. The 2% additional brightness corresponds to a forcing of about 4 watts per square metre and is akin to a doubling of CO2 concentrations.
- For various reasons, the greenhouse gas concentrations in past hot periods may not have been as high as we thought.
- We are introducing greenhouse gases into the atmosphere far more quickly than natural processes ever did. This might cause fast (positive) feedback effects to manifest themselves forcefully, before slower (negative) feedback effects can get going.
He also explains that the sharp warming that took place during the Paleocene–Eocene Thermal Maximum (PETM) were not caused by fossil fuels (which remained underground), but rather by the release of methane from permafrost and clathrates. If human emissions warm the planet enough to release that methane again, it could add a PETM-level warming on top of the warming caused by human beings.
Hansen’s conclusions are, frankly, terrifying:
The paleoclimate record does not provide a case with a climate forcing of the magnitude and speed that will occur if fossil fuels are all burned. Models are nowhere near the stage at which they can predict reliably when major ice sheet disintegration will begin. Nor can we say how close we are to methane hydrate instability. But these are questions of when, not if. If we burn all the fossil fuels, the ice sheets almost surely will melt entirely, with the final sea level rise about 75 meters (250 feet), with most of that possibly occurring within a time scale of centuries. Methane hydrates are likely to be more extensive and vulnerable now than they were in the early Cenozoic. It is difficult to imagine how the methane clathrates could survive, once the ocean has had time to warm. In that event a PETM-like warming could be added on top of the fossil fuel warming.
After the ice is gone, would Earth proceed to the Venus syndrome, a runaway greenhouse effect that would destroy all life on the planet, perhaps permanently? While that is difficult to say based on present information, I’ve come to conclude that if 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.
To re-emphasize the point, averting catastrophic or runaway climate change is the most important ethical and political task for those alive now, even if most politicians don’t yet realize it or don’t yet understand what that involves.
That last line also offers something to throw back, next time someone says the billions of dollars of revenue from exploiting the oil sands are simply to valuable to not collect.
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All this makes me feel a new clarity about where we should be concentrating our efforts.
They key battlegrounds are coal burning and unconventional oil and gas. If we can keep enough of that stuff in the ground, we can prevent catastrophic climate change. If we burn it all, disaster is all-but-inevitable.
Milan, your blog is the most spot on target.
The science exploration should be completely aimed toward determining how bad the situation is. You come close to describing it http://www.sindark.com/2008/02/27/ethics-among-the-doom ed/
We need to know whether we should go for adaptation, mitigation or endgame preparation. Big decisions ahead. Burning any carbon is foolish.
If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty.
One partial consolation is that tar shale requires more energy to extract than it contains. As long as that remains true, the chances of burning a lot of it are pretty low.
Of course, if we start approving nuclear reactors to steam the stuff out and upgrade it…
To me, it seems notable that the only three times ‘runaway climate change’ has been mentioned on the website of The Economist are times when it has been brought up by me.
They really aren’t anywhere close to appreciating what climate change could do to their entire worldview.
Study Says Undersea Release of Methane Is Under Way
By CORNELIA DEAN
Published: March 4, 2010
Climate scientists have long warned that global warming could unlock vast stores of the greenhouse gas methane that are frozen into the Arctic permafrost, setting off potentially significant increases in global warming.
Now researchers at the University of Alaska, Fairbanks, and elsewhere say this change is under way in a little-studied area under the sea, the East Siberian Arctic Shelf, east of the Bering Strait.
Natalia Shakhova, a scientist at the university and a leader of the study, said it was too soon to say whether the findings suggest that a dangerous release of methane looms. In a telephone news conference, she said researchers were only beginning to track the movement of this methane into the atmosphere as the undersea permafrost that traps it degrades.
But climate experts familiar with the new research, reported in Friday’s issue of the journal Science, said that even though it does not suggest imminent climate catastrophe, it is important because of methane’s role as a greenhouse gas. Although carbon dioxide is a far more abundant and persistent in the atmosphere, ton for ton atmospheric methane traps at least 25 times as much heat.
Until recently, undersea permafrost has been little studied, but work so far shows it is already sending surprising amounts of methane into the atmosphere, Dr. Shakhova and other researchers are finding.
In a telephone news conference on Wednesday, Dr. Shakhova said that permafrost in the East Siberian Arctic Shelf, peatland that flooded as sea levels rose after the last ice age, is degrading in part because runoff from rivers that feed the Arctic Ocean is warmer than it has been in the past.
She estimated that annual methane emissions from the East Siberian Arctic Shelf now total about 7 teragrams. (A teragram is 1.1 billion tons.) By some estimates, global methane emissions total about 500 teragrams per year.
Dr. Shakhova, who is also affiliated with the Russian Academy of Sciences, said that undersea methane ordinarily undergoes oxidation as it rises to the surface, where it is released as carbon dioxide. But because water over the shelf at most about 50 meters deep, she said, the gas bubbles to the surface there as methane.
As a result, she said, atmospheric levels of methane over the Arctic are 1.85 parts per million, almost three times as high as the global average of 0.6 or 0.7 parts per million. Concentrations over the shelf are 2 parts per million or higher.
But, “I am not the person to judge” whether the Arctic findings suggest that estimates of climate change in coming decades should be rewritten, she added.
“I would not go so far as to suggest any implications,” she said. “We are at the very beginning of research.”
Clarke’s First Law may also apply to the above: “When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.”
Hansen is 68, and was elected to the National Academy of Sciences in 1996. He has many other honours and awards.
That certainly doesn’t prove that runaway climate change is possible, but perhaps it provides a smattering of extra reason to take his opinion on the matter seriously.
Arctic Methane on the Move?
— david @ 6 March 2010
Methane is like the radical wing of the carbon cycle, in today’s atmosphere a stronger greenhouse gas per molecule than CO2, and an atmospheric concentration that can change more quickly than CO2 can. There has been a lot of press coverage of a new paper in Science this week called “Extensive methane venting to the atmosphere from sediments of the East Siberian Arctic Shelf”, which comes on the heels of a handful of interrelated methane papers in the last year or so. Is now the time to get frightened?
No. CO2 is plenty to be frightened of, while methane is frosting on the cake. Imagine you are in a Toyota on the highway at 60 miles per hour approaching stopped traffic, and you find that the brake pedal is broken. This is CO2. Then you figure out that the accelerator has also jammed, so that by the time you hit the truck in front of you, you will be going 90 miles per hour instead of 60. This is methane. Is now the time to get worried? No, you should already have been worried by the broken brake pedal. Methane sells newspapers, but it’s not the big story, nor does it look to be a game changer to the big story, which is CO2.
For some background on methane hydrates we can refer you here. This weeks’ Science paper is by Shakhova et al, a follow on to a 2005 GRL paper. The observation in 2005 was elevated concentrations of methane in ocean waters on the Siberian shelf, presumably driven by outgassing from the sediments and driving excess methane to the atmosphere. The new paper adds observations of methane spikes in the air over the water, confirming the methane’s escape from the water column, instead of it being oxidized to CO2 in the water, for example. The new data enable the methane flux from this region to the atmosphere to be quantified, and they find that this region rivals the methane flux from the whole rest of the ocean.
“In the geologic past through the glacial cycles the climate feedback from methane has been smaller than that from CO2. However, as you note we’re pushing CO2 beyond the limits of what it has been for millions of years. The methane hydrates in the ocean take millions of years to grow. So we may be pushing the hydrates to melt down in the future. We did calculations that if the feedback were too strong you’d see the hydrates melting down spontaneous throughout Earth history. You don’t really see that, so the upper limit we predicted was that the hydrates could ultimately release as much carbon as we burn in fossil fuels. But the time scale for that is thousands of years, so the impact on climate over the next few hundred years would be small compared to that from fossil fuel CO2.“
Methane May Be Building Under Antarctic Ice
* By Alexandra Witze, Science News Email Author
* March 16, 2010
* 3:39 pm
* Categories: Earth Science
BALTIMORE — Microbes living under ice sheets in Antarctica and Greenland could be churning out large quantities of the greenhouse gas methane, a new study suggests.
In recent years scientists have learned that liquid water lurks under much of Antarctica’s massive ice sheet, and so, they say, the potential microbial habitat in this watery world is huge. If the methane produced by the bacteria gets trapped beneath the ice and builds up over long periods of time — a possibility that is far from certain — it could mean that as ice sheets melt under warmer temperatures, they would release large amounts of heat-trapping methane gas.
Jemma Wadham, a geochemist at the University of Bristol in England, described the little-known role of methane-making microbes, called methanogens, below ice sheets on March 15 at an American Geophysical Union conference on Antarctic lakes.
Her team took samples from one site in Antarctica, the Lower Wright glacier, and one in Greenland, the Russell glacier. Trapped within the ice were high concentrations of methane, Wadham said, as well as methanogens themselves — up to 10 million cells per gram in the Antarctic sample and 100,000 cells per gram in Greenland. That’s comparable to the concentration of methanogens found in deep-ocean sediments, she said. The species of microbes were also similar to those found in other polar environments, such as Arctic peat or tundra.