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Climate Change, Irreversibility, and Urgency

Posted on 26 August 2012 by dana1981

This is a re-post from Bulletin of the Atomic Scientists of an article published by Richard C.J. Somerville, Distinguished Professor Emeritus and Research Professor at the Scripps Institution of Oceanography

Article Highlights

  • Two decades after the Earth Summit in Rio de Janeiro, most governments have agreed that limiting the increase in the average surface temperature of the Earth to 2 degrees Celsius above pre-industrial levels would represent a tolerable amount of global warming.
  • But the annual amount of human-caused global emissions of carbon dioxide, the main greenhouse gas driving climate change, is now about 50 percent larger than in 1992.
  • A failure to reduce carbon dioxide emissions significantly within the next decade will have large adverse effects on the climate that will be essentially irreversible on human timescales.

Climate scientists like to think of themselves as wise planetary physicians, explaining to the world what they have learned about climate and advising humanity on how to cope with the challenge of climate change. This metaphor can also appear attractive to policymakers and the public. Consider the appealing similarities between deciding what you should do about your weight and what the world should do about global warming. You can ask your doctor's opinion, but it is you who will determine your target weight. You can also ask your physician to recommend actions to reach that target. You can then experiment with diet and exercise, evaluate the results, and make changes. Throughout the process, you are in charge, and the physician's role is simply to advise.

There are obvious parallels with the climate change issue. Instead of body weight, the global average temperature at the surface of the Earth is the main metric. In place of your physician, the world has the combined expertise of the global community of climate scientists, as assessed by national academies of science and the Intergovernmental Panel on Climate Change. Deciding what climate change policies to adopt is up to the governments of all nations. Their first task is to decide how much global warming they regard as tolerable. Governments have scientific input, but they will also take into account risk tolerance, national priorities, economic impacts, and political considerations.

Suppose the world's governments could eventually manage to agree on a specific aspirational goal, such as limiting global warming to 2 degrees Celsius (3.6 degrees Fahrenheit) above the average temperature of the mid-1800s, a time before human activities had begun to affect the global climate significantly. Governments could next ask climate scientists what reductions in the emission rates of carbon dioxide and other heat-trapping gases would be needed to meet the 2 degree Celsius target. Then governments could negotiate with one another, aiming for a binding international agreement, with specific and enforceable emission-reduction levels and timetables for all countries. Science will thus have informed this process, but governments will have made all the policy decisions.

Can this approach succeed? Some environmental challenges have followed this script faithfully. One example is the apparently successful attempt to limit stratospheric ozone loss caused by manmade chemicals such as chlorofluorocarbons. Scientific research established the cause of the ozone loss. Then the political process -- with substantial scientific input -- quickly led to the Montreal Protocol and subsequent international agreements to halt the manufacture of ozone-depleting chemicals. This paradigm is often cited as a role model for limiting climate change to moderate levels.

The stratospheric ozone story unfolded quickly. The key scientific paper predicting ozone loss due to chlorofluorocarbons appeared in 1974, the discovery of severe Antarctic ozone depletion was published in 1985, and the Montreal Protocol entered into force in 1989. The international community, however, has already taken much longer, both scientifically and politically, to come to grips with the climate change issue, and the doctor's advice for dealing with the malady cannot be ignored much longer. A failure to reduce carbon dioxide emissions significantly and soon -- soon being within a decade or so -- will have large adverse effects that are, because of the physics and biogeochemistry of the climate system, essentially irreversible on human time scales. This is not an ideological or political assertion but an unavoidable consequence of a simple reality: Once excess carbon dioxide is added to the Earth's atmosphere, much of it will remain there for centuries or longer before natural processes remove it.

A century and a half of greenhouse gas research

Careful laboratory experiments by the Irish physicist John Tyndall, published in 1861, showed that water vapor, carbon dioxide, and certain other gases strongly absorb infrared radiation. Tyndall was the first to put the greenhouse effect on a firm empirical foundation, and he immediately recognized the potential implications for climate change.

In 1896, the Swedish chemist Svante Arrhenius calculated the sensitivity of climate to atmospheric carbon dioxide, asking how much global mean temperature would change if atmospheric amounts were doubled or halved. Through deep physical insight plus some good luck, Arrhenius obtained a result that is within about a factor of two of modern estimates.

In hindsight, it is easy to see that mankind had clear early warning about the need to rapidly reduce emissions of heat-trapping gases in order to avoid climate disruption. In the 1970s, two Swiss scientists carried out research that anticipated the challenge now confronting policymakers. Hans Oeschger and his doctoral student, Ulrich Siegenthaler, were pioneers in the development of Earth system models. Their 1978 paper in Science, based on simple models and limited data, concluded that, "For a prescribed maximum increase of 50 percent above the pre-industrial carbon dioxide level, the production [of carbon dioxide emissions] could grow by about 50 percent until the beginning of the next century, but should then decrease rapidly." They were right. The most recent research, with vastly better data and models incorporating a far more complete understanding of the climate system, has refined the quantitative conclusions and confirmed that essential result.

The political process, by contrast, has been extremely slow. The Earth Summit held in Rio de Janeiro in June 1992 was attended by more than 100 heads of nations and was widely praised as a landmark in environmental statesmanship. This conference produced the United Nations Framework Convention on Climate Change, a treaty signed by nearly every country on Earth. The objective of the treaty is to stabilize the amount of greenhouse gases in the atmosphere "at a level that would prevent dangerous anthropogenic interference with the climate system." Deciding what that "dangerous" level should be, however, is a task that the Rio negotiators left for the future.

Some 20 years later, most governments have now converged on a working definition of "dangerous." These governments have agreed that limiting the increase in the average surface temperature of the Earth to 2 degrees Celsius above pre-industrial levels would be a tolerable amount of global warming. Of course, this is a subjective decision, and some governments have argued for a lower and safer amount of warming. Officially, the European Union has accepted the 2 degree Celsius target as a concrete policy objective. Less formally, the Copenhagen Accord, endorsing the 2 degree goal, has been agreed to by some 141 countries, which together account for the great majority of the world's emissions of heat-trapping gases. This agreement, reached at December 2009 negotiations in Copenhagen, is not legally binding, however, and sets no concrete targets for emissions reductions.

And it must be said that very little significant progress has occurred toward actually making the large cuts in global emissions of heat-trapping gases that would be needed to meet the 2 degree goal. In fact, the annual amount of global carbon dioxide emissions from human activities is now about 50 percent larger than in 1992. These emissions increased the amount, or concentration, of carbon dioxide in the atmosphere by 10 percent during this 20-year period. This amount is now about 40 percent higher than it was in the mid-1800s. It is also an observed fact that the world has already warmed by about 0.8 degrees Celsius relative to the mid-1800s. That is nearly half the magnitude of warming judged to be tolerable by the Copenhagen Accord. Meanwhile, research and recent observations of the changing climate have shown that the effects of a 2 degrees Celsius warming may be far more disruptive than had earlier been thought. For example, in the range of 1 to 2 degrees Celsius warming, the area burned by wildfire in parts of western North America is expected to increase by a factor of two to four for each degree of warming. Other climate consequences in this range of seemingly moderate warming include large changes in precipitation, increases in extreme weather events, losses in food production, rises in sea level, reductions in stream flow in many river basins, and losses of Arctic sea ice.

A sobering outlook

Recent research indicates that the climate in coming decades and centuries will be largely determined by human activities. The natural factors that have led to large climate changes in the distant past, such as changes in solar luminosity and in the Earth's orbit, obviously still exist. These natural factors are simply too weak and too slow, however, to be significant over time scales of decades to centuries. On these time scales, human activities will dominate over natural factors. In particular, carbon dioxide is by far the most important heat-trapping gas produced by human activities, and the connection between atmospheric carbon dioxide amount and climate, while extremely complex in its details, can be summarized as follows: Substantial fractions of the carbon dioxide emitted into the atmosphere by human activities will remain in the atmosphere for centuries or longer. During that time, the carbon dioxide will become well-mixed by the winds, so that for climate purposes, the carbon dioxide concentration has effectively the same value everywhere on Earth. Even in the inconceivable event that emissions were to suddenly stop completely, the climate changes caused by carbon dioxide would persist for very long periods of time. The cumulative amount PDF of carbon dioxide emitted by human activities since the industrial revolution of the 1800s will largely determine the magnitude of the resulting climate change. For any specific target limit to global warming, such as 2 degrees Celsius, there is thus an allowed total amount of cumulative carbon dioxide emissions that must not be exceeded.

The quantitative implications of this scientific understanding are sobering. They confirm the 1978 insights of Siegenthaler and Oeschger. If global emissions of heat-trapping gases were to continue at current rates for the next 20 years, and then immediately cease entirely, the cumulative emissions will have exceeded the best estimate of the allowed amount, so the likelihood of meeting the 2 degree Celsius target would be low. Instead, in order to limit warming to 2 degrees Celsius, global emissions need to peak very soon, between now and about 2020, and then must decline rapidly. To stabilize climate, an almost completely decarbonized global world -- with near-zero emissions of carbon dioxide and other long-lived greenhouse gases -- needs to be achieved well within this century. More specifically, the average annual per-capita emissions will have to shrink to well below one metric ton of carbon dioxide by 2050. This is about 80 to 95 percent below the per-capita emissions in developed nations in 2000.

The climate system dictates a timescale for action

Decisions made by governments early in this century will have long-term consequences for the climate. Failure to take meaningful actions to reduce global emissions is a particularly serious decision. By continuing on its current path of increasing global carbon dioxide emissions, humanity is committing future generations to a strongly altered climate. Even beyond the current century, there are major implications for longer-term climate change. Higher temperatures and accompanying changes in climate caused by carbon dioxide emissions from human activity will be largely irreversible on human time scales. The effects are long-lasting. Atmospheric temperatures are not expected to begin to decrease substantially for many centuries to millennia, even after human-induced greenhouse gas emissions stop completely.

To meet the 2 degree Celsius target, the climate system itself thus imposes a timescale on when emissions need to peak and then begin to decline rapidly. Scientific understanding of this timescale shows that mitigation of climate change is urgent and cannot wait. A window of opportunity to decrease emissions has been open for several decades but will soon close and will remain closed. This urgency is thus not ideological or political, but rather is due to the long residence time of atmospheric carbon dioxide and the resulting near-irreversibility of climate change for centuries or longer. This is a critical shortcoming of the medical metaphor that likens the climate change problem to the task of an individual trying to reach a target body weight. If your current weight is higher than your target, medical science can advise you on how to lose weight. If the amount of carbon dioxide in the atmosphere becomes higher than the amount compatible with the desired limit on global warming, however, the warming will exceed the target. There is no proven technology for removing large amounts of carbon dioxide from the atmosphere economically.

In short, the urgency of acting to mitigate climate change is directly linked to the physics and biogeochemistry of the climate system. An enduring failure to achieve meaningful science-based international agreements to rapidly reduce emissions of heat-trapping gases will inevitably have serious consequences for the degree of climate change that the Earth will undergo. If the world as a whole continues to procrastinate throughout the current decade, allowing emissions to continue to increase year after year, then it will almost certainly have lost the opportunity to limit warming to 2 degrees Celsius. Instead, our children and their descendants, and ultimately all living things, will be faced with the consequences of more severe climate disruption.

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Comments 1 to 11:

  1. Just a brief, entirely off-topic, heads up... The Guardian's thread on sea ice appears to have been entirely highjacked, see pages 14-16 of comments, by a learned theological discussion of the state of John Cook's soul. I thought perhaps Mr Cook might like to be aware of this, and might even like to comment. I need hardly say that this is extremely sticky ground, and the potential for causing offence probably limitless, but... Please do feel free to remove this comment from this thread.
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  2. idunno: ...a learned theological discussion of the state of John Cook's soul. Guaranteeing thereby that somebody is entertaining a desperate wish to avoid the actual topic of the Guardian article. Sadly pathetic. Meanwhile, back more or less on topic: Science adviser warns climate target 'out the window' Lack of phase coherence here. From the blog post above: "A failure to reduce carbon dioxide emissions significantly within the next decade will have large adverse effects on the climate that will be essentially irreversible on human timescales." I'd say that the situation in the Arctic is a "large adverse effect" and that it's "essentially irreversible on human timescales," or at least the timescale available to those of us reading this. What's our urgent action item in the Arctic? Engaging in a mad rush to extract for combustion the hydrocarbons newly available thanks to vanishing ice. Can anybody see a reason for optimism? I can't.
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  3. Idunno. Thanks for the heads up. We had already noticed that thread going a bit feral. Sometimes not a good idea to get into some fights. Doug. No not much cause for optimism no. But a glimmer. A few things. The cost of solar PV cells is plummeting due to mass production in China. Here in Australia people are putting solar panels on new houses based on cost alone. The savings in energy demand mean we have managed to avoid needing to build a new FF power station. The huge decline in sea ice in the Arctic this year has been spectacular to watch and it ain't over yet. All the trend lines are still plummeting. Whats good about that? The silver lining is that if we are going to get far greater action then the mass population has to get behind the need for it. Paul Gilding in his book The Great Disruption had one chapter labelled "When the dam of Denial Breaks". And thats what we need. Dramatic events that will shake the world up and wake it up. The Arctic going ice free a few years earlier than was expected does't matter as much in terms of what the long term consequences of global warming will end up being. Just one brick in the wall falling into place a little earlier than though. But if that gets action happening faster it might be worth the price.
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  4. The rapidity of Arctic sea ice loss and the awakening of a the methane "time bomb" across the once frozen regions of the NH is something the 2007 IPCC report didn't take into account at all. Limiting increase in global temps to 2C is out the window and 3C may be impossible to avoid now as well. Those fools who think that a melting Arctic is a great opportunity to plan for further fossil fuel extrapolation fail to understand the various stresses this will placec on a civilization needing to feed 7+ Billion humans.
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  5. I just commented on the latest Arctic sea ice thread about the urgency of humanity's response (or lack thereof) to climate change. To hark to that other great denial of science we're basically at the point where the patient is coughing up blood, and his doctor is telling him that he should have already given up smoking if he doesn't want to die of lung cancer. And the patient continues to smoke, because he doesn't (want to) believe his doctor when said physician tells him that the patient's addiction has already killed him. I'm also reminded of one of the few episodes of The Mentalist to which I (ironically) exposed myself...
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  6. It is time to recall the terrific rant by Michael Tobis at A half dozen paragraphs down. A year an a half ago. It still holds up well.
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  7. The article compares the Ozone hole issue with climate change and the common effort of mankind to reduce the ozone hole ... I had some time ago the same idea ... however: Ozone hole issue had an alternative: other material instead of the Ozone killer stuff to put into the "icebox" ... whereas Climate Change: I do not know an alternative for energy production at the Terawatt dimension ... We are working on alternative energy production - compared to the terawatt-issue still small ... and therefore it needs TIME ... Also: One thing on the long run to do (possibly): eliminate CO2 from flue gases of the big coal power plants by filtering. Now the only way to do that is by multistage filtering... (it would be nice to do that [the filtering] with normal air - but that is ineffective - at present) Then: what to do with the CO2? Sequestration is one possibility - we had this here at SKS. Another would be: algae growth in the neighbourhood of the power plant which however makes necessary areas about 34 km-squared for algae plants - who has that area except the U.S.? Another would be: the Sabatier Process making CH4 or Methanol (CH3OH) from CO2 with H2 from alternative energy sources ... But that is all far from reality at least compared to the Terawatt issue ... perhaps realized in 10 or 20 years ... However: we have to start ... Let us begin ...
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  8. The thing about ozone was the main use of the offending chemicals was as a refrigerant. There was $1 worth of CFC in a refrigerator. Compare to the place fossil fuels have in the overall scheme of things. The other thing was the way scientific understanding evolved after the issue had been successfully relegated to a back burner by industry lobbying efforts. After an initial culture shock when Rowland discovered what was possible in 1973 and consumers turned away from spray bomb cans powered by substances that could destroy Earth's radiation shield, industry got things quieted down enough so that the fastest expanding use of CFCs in the 1980s was for use in foam hamburger containers. The general scientific understanding (with notable exceptions, i.e. Rowland, etc.) of the scientific community studying ozone depetion around 1986 was that the models were showing that it shouldn't be possible, yet, to observe that ozone had depleted anywhere, and, most thought, you couldn't observe that ozone had depleted anywhere. (Rowland kept wandering around shouting what about this, what about that). There was a general agreement that just doing nothing and allowing production of CFCs and the other chemicals to expand without limit would at some point pose a very serious problem. The debate drifted off.... Rowland kept saying there's a problem now. Hansen seems to have the role Rowland played in the ozone debate, in the climate debate now. You could be as depressed about the prospects for civilization over ozone depletion and why nothing was being done then as people who've read too many climate science papers are now. Then Farman published his observations of the Antarctic ozone hole. So suddenly, the general understanding went from nothing observable was happening yet to there's this hole in the ozone you could see from Mars. Everyone coalesced around the view that this is the sh*t and it is hitting the fan NOW. At some levels in the stratosphere all the ozone was gone. A reaction was suddenly triggered, it seemed, and poof. Everyone realized no one had a clue about the chemistry that was causing this. The word "hysteria" was applied to the scientific community by observers. Civilization received a shock. For a brief while. The combination, that the problem was basically trivial to solve, and this sudden shock rippling out from the scientists, got a political response that may yet prove inadequate, that nevertheless many point to as a precedent of success. (See Anderson's recent discovery that climate change may have changed the behaviour of thunderstorms causing them to inject water deeper into the stratosphere than it has been during the time civilization has been around, where it is liable to trigger exactly what has been going on over Antarctica all these years... Harvard Magazine article here) By trivial I mean it didn't amount to a hill of beans whether you kept on using $1 worth of chemicals in each refrigerator or you retooled to produce and use $4 per refrigerator or something like that. The US Senate passed a resolution 80 - 2 calling on Reagan to act. Reagan personally overruled the remaining Neanderthals in his Administration who were still arguing that nothing should be done, and the US backed beefing up the Montreal Protocol. Compare to the climate problem: replacing 80% or more of the energy source to civilization is a bit more daunting than paying $3 more for a fridge. And that doesn't address the GHGs coming from land use, food production, et. cetera. And we've become like drug addicts who need a bigger dose for less effect: the surprise that the great ice sheets are waking up, or the massive loss of summer sea ice in the Arctic, didn't cause enough political action to see in the rising CO2 chart. You can still make an argument we don't have the equivalent of the ozone hole just yet. We need something like the US Southwest actually turns into a duplicate of the Sahara, or a Category 6 250 mph hurricane levels the Florida peninsula. If political action doesn't come after that.... These warnings that this or that is going to happen UNLESS just aren't the equivalent. And this is a real problem how far the disrespect for science now extends. You had real difficulty showing your face at the highest levels of civilization if your line was the scientists are all just making this up, back then.
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  9. I am more pessimistic than ever that events, science, or argument will convince people to change. I think the best we can do is point out to The Patient, that they are Overweight, that they need to cut out the cigarette smoking and whiskey drinking, and they need more exercise. If they choose not to do so, it is Their Choice. The Hard Part is that Our Own Kids will suffer the consequences, too. I have no realistic answers. All human systems have limitations. The United States Constitution is ingenious, but why should we expect it itself hasn't limits? Maybe global challenges like climate change are just too tough for it to successfully solve. I am less concerned about predictions like extreme storms and droughts than I am about the nonlinear bifurcations in the climate system which may be possible, because we are operating in paleo-historically unprecedented parts of the state space. Basis? See
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  10. Like other people on this thread I'm becoming increasingly worried. What makes it more difficult is that as I carry on my day to day living I have nobody to talk to who really gets the urgency. The general attitude of those who at least accept the science seems to be, oh they'll do something about it, they won't let the worst happen. But it's clear to me that they will -- humans don't react until their backs are unequivocally against the wall. I mean; even the rapid Arctic ice loss seems to be being cast as an opportunity. They see the silver lining, not the black cloud. It seems clear to me that, in the natural world, change tends not to happen in a smooth progression; it happens in fits and starts as various tipping points, large and small, occur. It's like a dam slowly filling to the point it gives way, or a river overflowing and breaking its banks, or the tension building up in tectonic plates until an earthquake occurs. Anyone who expects climate change to occur in a steady and manageable progression, giving time to adapt, is deluded and, frankly, dangerous. Frighteningly, it seems that everyone with money and power is in that category. It's psychiatry we need, even more than climate science.
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  11. "It seems clear to me that, in the natural world, change tends not to happen in a smooth progression; it happens in fits and starts as various tipping points, large and small, occur." John, in case you're not aware of it, here's a link that robustly supports your supposition. Punctuated equilibria As a geologist, one of the most stark examples of this is the Burgess Shale, in Canada. I am *very*, very worried we're at, if not past, an imprtant tipping point in our 'open, uncontrolled' experiment with the world's biosphere. My experiences at Biosphere II, and knowing its intimate history, also have led me to the same point as your last statement. "It's psychiatry we need, even more than climate science."
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