Sunday, May 3, 2009

Total emisions approach - accurate but not novel and a flawed basis for policy

As this report on the new studies published in Nature indicates, the global warming problem is and always has been understood to be a matter of the total loadings of GHG emissions in the atmosphere, not a matter of timing.  The timing of the GHG emissions only matters over the course of centuries because eventually greenhouse gases emitted into the atmosphere decompose.  I don't think that anyone familiar with climate policy has ever believed otherwise.  So, on that score the new studies are not new, but they may alter how the problem is conceptualized for policy purposes.

Policy cannot simply divide the total allowable emissions among nations and be done with it.  First, absent intermediate goals tied to deadlines, countries cannot monitor each others compliance with reduction targets.  Second, it creates a tendency for nations to believe that they can just wait until 2050 or whatever when technology will save them and voila they will become carbon neutral.  Our experience in the Clean Air Act attainment with NAAQS was that, faced with a deadline and no requirement for annual progress, states just planned to do something at the last moment and when their plans didn't work, they threw up their hands and said, "OH well." 

We cannot afford to use that model of regulation with respect to climate.  Instead, we need to use technology-forcing technology based standards (e.g. no new coal plants without CSS; CSS retrofit for existing fossil-fuel plants by 2020) along with streamlining the ability of renewables to come online and planning ala the 1990 Clean Air Act amendments with annual progress requirements and contingency measures built into the plan.  Those approaches would be far more successful than the "consume up to the last moment" strategy that may be encouraged by the total emissions approach.

Lawyers have to leave science to the scientists and use extreme care when they are working on a cross-disciplinary basis.  But scientists need to be just as wary of providing policy concepts unencumbered by an understanding of past performance of various regulatory approaches.


From: Naomi Antony, Science and Development Network

Published April 30, 2009 10:40 AM
Scientists put carbon ceiling at a trillion tonnes

Scientists hope a new approach to assessing carbon build-up in the atmosphere will simplify issues
for policymakers and economists. Two papers published in Nature today (29 April) show that the
timings of carbon emissions are not relevant to the debate — it is the total amount of carbon dioxide
emitted over hundreds of years that is the key issue.

Rather than basing negotiations on short-term goals such as emission rates by a given year,
the researchers say the atmosphere can be regarded as a tank of finite size which we must not
overfill if we want to avoid a dangerous temperature rise.

Climate policy has traditionally concentrated on cutting emission rates by a given year, such as
2020 or 2050, without placing these goals within the overall context of needing to limit cumulative
emissions.

Both papers analyse how the world can keep the rise in average surface temperatures
down to no more than two degrees Celsius above pre-industrial levels. This figure is
widely regarded as the threshold beyond which the risk of dangerous climate change
rapidly increases. Policymakers around the world have adopted this limit as a goal.

The first study, led by Myles Allen from the University of Oxford, UK, found that
releasing a total of one trillion tonnes of carbon dioxide into the atmosphere
between 1750 and 2500 would cause a "most likely" peak warming of two degrees
Celsius. Emissions to 2008 have already released half of this. Allen said in a
press briefing this week (27 April): "It took 250 years to burn the
first half trillion tonnes and, on current predictions, we'll burn the next half
trillion in less than 40 years."

The second study, led by Malte Meinshausen at the Potsdam Institute for Climate
Impacts Research, Germany, used a computer model to demonstrate that to avoid
exceeding two degrees Celsius by 2100, cumulative carbon emissions must not exceed
0.9 trillion tonnes. "We have already emitted a third of a trillion in just the past nine years,"
Meinshausen says.

David Frame, a co-author of the Allen paper and researcher at the University of
Oxford, said that these findings make the problem "simpler" than it's often
portrayed. "[The findings] treat these emissions ... as an exhaustible resource. For
economists, this way of looking at the problem will be a huge simplification," Frame
said. "Basically, if you burn a tonne of carbon today, then you can't burn it tomorrow
" you've got a finite stock. It's like a tank that's emptying far too fast
for comfort. If country A burns it, country B can't. It forces everyone to consider
the problem as a whole."

In a separate essay, Stephen Schneider of the Woods Institute for the Environment at
Stanford University in the United States, discusses what a world with 1,000 parts
per million of carbon dioxide in its atmosphere might look like.

This article is reproduced with kind permission of the
Science and Development Network (SciDev.Net).
For more news and articles, visit www.scidev.net.



Nature Abstract of Allen letter:

Warming caused by cumulative carbon emissions towards the trillionth tonne

Myles R. Allen1, David J. Frame1,2, Chris Huntingford3, Chris D. Jones4, Jason A. Lowe5, Malte Meinshausen6 & Nicolai Meinshausen7

  1. Department of Physics, University of Oxford, OX1 3PU, UK
  2. Smith School of Enterprise and the Environment, University of Oxford, OX1 2BQ, UK
  3. Centre for Ecology and Hydrology, Wallingford, OX10 8BB, UK
  4. Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK
  5. Met Office Hadley Centre (Reading Unit), Department of Meteorology, University of Reading, RG6 6BB, Reading, UK
  6. Potsdam Institute for Climate Impact Research, 14412 Potsdam, Germany
  7. Department of Statistics, University of Oxford, OX1 3TG, UK

Correspondence to: Myles R. Allen1 Correspondence and requests for materials should be addressed to M.R.A. (Email: myles.allen@physics.ox.ac.uk).

Top

Global efforts to mitigate climate change are guided by projections of future temperatures1. But the eventual equilibrium global mean temperature associated with a given stabilization level of atmospheric greenhouse gas concentrations remains uncertain1, 2, 3, complicating the setting of stabilization targets to avoid potentially dangerous levels of global warming4, 5, 6, 7, 8. Similar problems apply to the carbon cycle: observations currently provide only a weak constraint on the response to future emissions9, 10, 11. Here we use ensemble simulations of simple climate-carbon-cycle models constrained by observations and projections from more comprehensive models to simulate the temperature response to a broad range of carbon dioxide emission pathways. We find that the peak warming caused by a given cumulative carbon dioxide emission is better constrained than the warming response to a stabilization scenario. Furthermore, the relationship between cumulative emissions and peak warming is remarkably insensitive to the emission pathway (timing of emissions or peak emission rate). Hence policy targets based on limiting cumulative emissions of carbon dioxide are likely to be more robust to scientific uncertainty than emission-rate or concentration targets. Total anthropogenic emissions of one trillion tonnes of carbon (3.67 trillion tonnes of CO2), about half of which has already been emitted since industrialization began, results in a most likely peak carbon-dioxide-induced warming of 2 °C above pre-industrial temperatures, with a 5–95% confidence interval of 1.3–3.9 °C.

  1. Department of Physics, University of Oxford, OX1 3PU, UK
  2. Smith School of Enterprise and the Environment, University of Oxford, OX1 2BQ, UK
  3. Centre for Ecology and Hydrology, Wallingford, OX10 8BB, UK
  4. Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK
  5. Met Office Hadley Centre (Reading Unit), Department of Meteorology, University of Reading, RG6 6BB, Reading, UK
  6. Potsdam Institute for Climate Impact Research, 14412 Potsdam, Germany
  7. Department of Statistics, University of Oxford, OX1 3TG, UK

Correspondence to: Myles R. Allen1 Correspondence and requests for materials should be addressed to M.R.A. (Email: myles.allen@physics.ox.ac.uk).









									
									
									

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Posted by: Green Crusader | Jun 11, 2009 6:26:56 AM

Hi, Just some quick comments; the nice things about the Allen et al paper (to me, at least) are that (1) it finds a better-constrained relationship between emissions and peak temperature than any we have been able to find between emissions and equlibrium warming (the default way of framing the problem); (2) this exploits the fact that long timescale processes, which are responsible for much of the uncertainty in equilibrium warming, can be ignored if the forcing is short compared to those long timescales; (3) and this results in a nice "exhaustible resource" reframing of the problem which; (4) happens to be pretty tractable for economists.

The first and second of these, within a reasonably formal way of tracing uncertainties through the problem *are* novel, though of course the idea of treating emissions as an exhaustible stock isn't: Tom Wigley and Wally Broecker have published on this recently, and we've been arguing it for about 4 years, too. The quantification we get for the relationship between cumulative emissions and peak warming ought to be handy for economists, who can fairly easily (I think) incorporate the uncertainty information in the study.

"[...] it creates a tendency for nations to believe that they can just wait until 2050 or whatever when technology will save them and voila they will become carbon neutral."
Well... this is one for the integrated assessment community and their discontents. The contribution Allen et al can make here is to give them inputs which tie climate mitigation and damages together in a better-constrained way than we have been able to do before. Obviously we haven't said anything like your sentence above: we all realise that the issue of optimal paths to an unburnt trillionth tonne is value-laden, amongst other things, and much more about socioeconomic possibilities than scientific analysis.

"Policy cannot simply divide the total allowable emissions among nations and be done with it."
Totally agree - this is a normative issue for the negotiations process to deal with, though you could have a conversation about efficiency by discussing auctioning vs other allocative mechanisms. Interesting stuff, but not one that scientists are very well-qualified to contribute to.

Dave

Posted by: Dave Frame | May 9, 2009 6:01:39 AM

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