A new study from the National Oceanic and Atmospheric Administration has some startling news: some of the effects of global warming are irreversible. Even if we suddenly stopped all CO2 emissions today certain effects that we are already feeling will still be with our descendants a thousand years from now. If we continue to increase our emissions of CO2 the number of irreversible effects will be that much greater.
It is often assumed that if we halt CO2 emissions within the next few years that the world will return to it’s pre-Climaticide state within a century or two. That is not the case according to a report to be published this week [as of 4pm PST the paper does not show up on the PNAS web site] in the Proceedings of the National Academy of Sciences by Susan Solomon of the Earth System Research Laboratory in Boulder, Colorado.
Examples of global warming effects that will still be felt a 1000 years after CO2 emissions are stopped, include changes in surface temperature, rainfall, and sea level.
The study examines the consequences of allowing CO2 to build up to several different peak levels beyond present-day concentrations of 385 parts per million and then completely halting the emissions after the peak. The authors found that the scientific evidence is strong enough to quantify some irreversible climate impacts, including rainfall changes in certain key regions, and global sea level rise.
The scientists emphasize that increases in CO2 that occur in this century “lock in” sea level rise that would slowly follow in the next 1,000 years. Considering just the expansion of warming ocean waters—without melting glaciers and polar ice sheets—the authors find that the irreversible global average sea level rise by the year 3000 would be at least 1.3–3.2 feet (0.4–1.0 meter) if CO2 peaks at 600 parts per million, and double that amount if CO2 peaks at 1,000 parts per million.
“Additional contributions to sea level rise from the melting of glaciers and polar ice sheets are too uncertain to quantify in the same way,” said Solomon. “They could be even larger but we just don’t have the same level of knowledge about those terms. We presented the minimum sea level rise that we can expect from well-understood physics, and we were surprised that it was so large.”
I cannot emphasize too much that Solomon is describing a minimum, conservative, non-real world, best-case scenario. For example, the sea level rise that Solomon and her colleagues describe is only the result of thermal expansion. It does not include sea-level rise from the melting of the Greenland and Antarctic ice sheets or Alpine glaciers, which, should they occur, will, because of various feedbacks (reduced albedo, increased and methane release from permafrost melting, as well as other related marine issues not directly related to sea level rise such as ocean acidification) take place much more rapidly and raise the sea level much more dramatically, potentially over decades and by 100’s of feet not the the 3 feet that Solomon is talking about.
What Solomon is saying is that even if we stabilize atmospheric CO2 at 600 ppm by the year 3000, the oceans will have risen 3 feet. If we stabilize at 1000 ppm they will have risen by 6 feet.
One might be inclined to respond to this by saying, “So, what? A six foot sea-level rise over a thousand years. Surely, humanity can adapt to that. And surely it could.
Far more worrisome is what Solomon writes about drought:
If CO2 is allowed to peak at 450-600 parts per million, the results would include persistent decreases in dry-season rainfall that are comparable to the 1930s North American Dust Bowl in zones including southern Europe, northern Africa, southwestern North America, southern Africa and western Australia.
The study notes that decreases in rainfall that last not just for a few decades but over centuries are expected to have a range of impacts that differ by region. Such regional impacts include decreasing human water supplies, increased fire frequency, ecosystem change and expanded deserts. Dry-season wheat and maize agriculture in regions of rain-fed farming, such as Africa, would also be affected.
In other words, if CO2 is allowed to peak at the 450-600 ppm, instead of the 350 ppm that James Hansen (PDF) and Al Gore are insisting upon, (but which many climate scientists don’t believe is possible to achieve–see Joe Romm’s series on this question) we will have inevitably, irreversibly locked ourselves into a 1000-year long 1930’s style dustbowl over a very large part of the earth’s surface. And, remember, that that is the most optimistic scenario. That’s right the most optimistic scenario is one in which large parts of the earth’s surface are a desert completely unsuited to agriculture or human occupation for at least a millennium.
You can watch Solomon comment on her work in the video below:
Kevin Trenberth, a climatologist at the National Center for Atmospheric Research, said [of Solomon's study that] it’s an important message for the wider public to grasp. “This aspect is one that is poorly appreciated by policymakers and the general public: Many aspects of the changes that are slowly coming are not really or practically reversible,” he said.
It’s not hard to imagine how the denialists/delayers will respond to this research. They will focus on the long time period that Solomon and her colleagues consider and will conclude that nothing needs to be done currently, despite the fact that Solomon herself is calling for urgent action.
As an example here is the reaction of Roger Pielke Jr. one of the most prominent delayers.
Roger Pielke Jr., a climate policy specialist at the University of Colorado, said the study would not likely “change the nature of the debate” about cutting emissions, at least in the short term.
“Decisions are going to be made about mitigation based on short-term costs and benefits of those actions,” he said. “In the very long term, if things turn out to be as bad as projected … then we’ll have technologies to do that.”
The same old denialist/delayer arguments: “It’s too expensive to do anything now, but later we will have miraculous technology that will make all this go away and save us. So, no need to worry.”
Kevin Trenberth, a climatologist at the National Center for Atmospheric Research responded to Pielke Jr. in the following terms:
“The policy relevance is clear: We need to act sooner, even if there is some doubt about exactly what will happen,” he said. “By the time the public and policymakers really realize the changes are here, it is far too late to do anything about it. In fact, as the authors point out, it is already too late for some effects.”
A. Siegel had an interesting post on the NOAA report over at Daily Kos entitled A few decades of prevention vs 1000 years of Hell … I usually agree with Adam on global warming issues, but I have some doubts about his position on this one because I don’t see how we can pull off the prevention part. I am myself a supporter of the 350 ppm target but I have yet to see anyone provide a convincing description of how such a goal can be achieved taking into account both the technical and political (domestic and international) issues. I think that we will be lucky to stabilize CO2 emissions at 450 parts per million, which means, if Solomon and her team are correct, we are doomed to an inevitable worldwide dustbowl, as our best long-range outcome. Far more likely is that things will be much worse because as I pointed out above, Solomon’s forecast is a best-case one, in which most of the terrible things that can happen (and some of which, I believe, are likely to happen) are left out. What we are more likely to get, in my opinion is, if I may tinker with Adam’s title a bit, “A few decades of prevention AND 1000 years of hell…”
By all means, let us do all that we can, because however bad things turn out to be, they will inevitably be worse if we fail to do everything within our power to contain this monster we have unleashed. But we all need to be realistic enough to know that he battle is no longer between the world that we knew and the one that we have created. Rather, it is between the one we have created and a far worse one that we will create if we do not give our all and as urgently as possible.