It’s Crunch Time

Updated: See additional related story links at the end of this post.

It seems we now have a new way of measuring the urgency of the climate chaos situation.

Green Car Congress: Study Concludes That to Limit Global Warming to 2 °C, Less Than 25% of Proven Fossil Fuel Reserves Can be Burnt Between Now and 2050 (emphasis added):

Less than a quarter of the proven fossil fuel reserves can be burnt and emitted between now and 2050, if global warming is to be limited to two degrees Celsius (2 °C), according to a new study published in the journal Nature today. This issue of Nature—themed “The Climate Crunch”—features a number of related papers and commentary on greenhouse gas emissions and the difficulty of cutting back, as well as an editorial calling on commitment from “the highest levels” to make the needed changes.

The study, led by Malte Meinshausen at the Potsdam Institute for Climate Impact Research (PIK), calculated how much greenhouse gas emissions can be pumped into the atmosphere between now and 2050 to have a reasonable chance of keeping warming lower than 2 °C (above pre-industrial levels)—a goal supported by more than 100 countries to prevent dangerous climate change.

The researchers, involving scientists from Germany, the United Kingdom and Switzerland, concluded that the limit is 1,000 billion tonnes of carbon dioxide between the years 2000 and 2050. The world has already emitted one third of that in just nine years.

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The study used a single, efficient computer model which incorporated the effects of all greenhouse gases, aerosols and air pollutants, and the range of possible responses of the carbon cycle and earth’s climate system. This was combined with about a thousand emission pathways.

The study explicitly takes into account the uncertainties related to modeling climate change. Throughout the study, probability statements were used to summarize the current level of knowledge based on observational data. It also used a huge number of different simulation results from the latest assessment report of the Intergovernmental Panel on Climate Change. In taking this comprehensive approach the researchers went a step further than previous work.

Unfortunately, I can’t access the series of articles without paying $32 for each one (and I honestly can’t afford to buy access to even a small portion of the paid-access articles that come across my screen), so I can’t read them or give you a link. (See the end of the GCC article above for DOI links to the articles’ abstracts.)

You can, however, read an editorial from that issue, Time to act:

It is not too late yet — but we may be very close. The 500 billion tonnes of carbon that humans have added to the atmosphere lie heavily on the world, and the burden swells by at least 9 billion tonnes a year (see page 1117). If present trends continue, humankind will have emitted a trillion tonnes of carbon into the atmosphere well before 2050, and that could be enough to push the planet into the danger zone. And there is no reason to think that the pressure will stop then. The coal seams and tar sands of the world hold enough carbon for humankind to emit another trillion tonnes — and the apocalyptic scenarios extend from there (see page 1104).

Nations urgently need to cut their output of carbon dioxide. The difficulty of that task is manifest: emissions have continued to rise despite almost two decades of rhetoric, diplomacy and action on the matter. But that unhappy fact should not be taken as a licence for fatalism. Governments have a wide range of pollution-cutting tools at their command, most notably tradable permit regimes, taxes on fuels, regulations on power generation and energy efficiency, and subsidies for renewable energy and improved technologies. These tools can work if applied seriously — so citizens around the world must demand that seriousness from their leaders, both within their individual nations and in the international framework that will be discussed at the United Nations Climate Change Conference in Copenhagen this December.

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The latest scientific research suggests that even a complete halt to carbon pollution would not bring the world’s temperatures down substantially for several centuries. If further research reveals that a prolonged period of elevated temperatures would endanger the polar ice sheets, or otherwise destabilize the Earth system, nations may have to contemplate actively removing CO2 from the atmosphere. Indeed, the United Nations Intergovernmental Panel on Climate Change is already developing scenarios for the idea that long-term safety may require sucking up carbon, and various innovators and entrepreneurs are developing technologies that might be able to accomplish that feat (see page 1094). At the moment, those technologies seem ruinously expensive and technically difficult. But if the very steep learning curve can be climbed, then the benefits will be great.

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More radical still is the possibility of cooling the planet through some kind of ‘geoengineering’ that would dim the incoming sunlight (see page 1097). The effects of such approaches are much more worrying than those of capturing carbon from the air, however. The cooling from geoengineering would not exactly balance the warming from greenhouse gases, which would cause complications even if the technology itself was feasible — something for which the evidence has been circumstantial, at best.

But discussions about the possibilities offered by geoengineering could also lull the world’s leaders into complacency — if they lead them to believe that the technology will provide an escape hatch if the climate ever does reach a tipping point. This does not mean that the discussions should be avoided, but rather that the speculations need to be backed up with a solid body of research. Moreover, geoengineering research should be framed not as a hope for deus ex machina fixes to sudden global deterioration, but as a palliative cushion for the worst excesses of the peak years that are inevitable even after emissions start to be cut. A world slightly shaded from the Sun while its carbon levels are brought down by means of active capture would be a strangely unnatural place — but not necessarily a bad one, compared with the alternatives.

A few thoughts here:

• We need more than a 50% reduction from 1990 levels by 2050? The number I’ve heard repeated (and repeated myself) endlessly is that we need 80% by 2050, so this conclusion is not a raising of the bar.
• Casting the situation as a limit on how much of the remaining fossil fuels we can burn in a given time window strikes me as extremely useful. I don’t mean to suggest that legislators and deniers around the world will suddenly slap themselves in the forehead and exclaim, “Oh! Now I get it! Let’s get to work!” But it does seem like a much more approachable way to frame the limits to our behavior than is talking about parts per million of CO2 in the atmosphere. (I’m assuming that the math all works out, and that the authors used reasonable, mainstream estimates for the recoverable reserves of fossil fuels.)
• I’m glad to see the notable hesitance over geo-engineering, as expressed in the editorial quoted above. On a related note, see Alex Steffen’s post on ClimateProgress about geo-engineering.
• Also worth a read is RealClimate: Hit the Brakes Hard; a couple of the authors appearing that issue of Nature are RealClimate authors.
• I would love to know more detail about how the climate model handled positive feedbacks. As I’ve pointed out countless times here in recent months, we keep finding new ones or making unpleasant discoveries about the ones we already knew about. I think there’s a better than 50/50 chance that in just a couple of years we’ll have accumulated enough new examples of of these nasty surprises to conclude that these studies were too optimistic.
• As I’ve said before, I have very little confidence that we both have and will wisely use the time before we’re at the point of a runaway climate change. In other words, I think the most likely scenario is that we’ll have no choice but to resort to one or more geo-engineering options in addition to very aggressive cuts in carbon emissions.

See also:

• Climate Progress: Must have PPT in disappointing issue of Nature devoted to “The Coming Climate Crunch”
• BBC: ‘Safe’ climate means ‘no to coal’
• New Scientist: Humanity’s carbon budget set at one trillion tonnes
• AP: To keep warming low, deeper pollution cuts needed
• Reuters: World can burn 25 percent of oil, coal safely: study
• AFP: To meet climate goal, cut fossil fuels use: study
• Scientific American: How Much Is Too Much?: Estimating Greenhouse Gas Emissions