Related to the draw down issue, there is this interesting new post by Monbiot on ‘biochar’ — a pretty harsh critique:
http://www.monbiot.com/archives/2009/03/24/woodchips-with-everything/

“Kevin Rudd was explaining the benefits of clean coal technology during a meeting with the coal industry today when he said the necessary stabilising point to tackle climate change is an emissions level of 450 parts per million by 2050.”

referencing a CO2 ppm target! very impressive!

Garnaut was referring to 455 ppm CO2-eq in terms of the effect of all GHGs currently in the atmosphere without any reduction for the cooling effects of aerosols.

The IPCC (2007: 102) summarised the effects of GHGs and aerosols as follows:

“Atmospheric CO2 concentrations [reached] 379 ppm in 2005 … The direct effect of all the long-lived GHGs is substantial, with the total CO2 equivalent concentration of these gases [in 2005] estimated to be around 455 ppm CO2-eq (range: 433-477 ppm CO2-eq). The effects of aerosols and landuse changes reduce radiative forcing so that the net forcing of human activities is in the range of 311 to 435 ppm CO2-eq, with a central estimate of about 375 ppm CO2-eq.”

Here is my explanation of the background to these figures and the term “carbon dioxide equivalents” (Nb. I am lawyer, not a climate-scientist like Barry or Ian so take this with a grain of salt. It comes from an article I wrote in a law journal last year):

——————————————————–

For ease of comparison and modelling greenhouse gas emissions and atmospheric concentrations are commonly measured in a standard unit known as “carbon dioxide equivalents” (CO2-e or CO2-eq). This term is defined and used in slightly different ways in the context of emissions and atmospheric concentrations of greenhouse gases. The unifying theme for the different uses is that they allow the effect of different greenhouse gases to be compared using carbon dioxide as a standard unit for reference. It may be noted also that some authors and inventories refer to “carbon equivalents” when discussing quantities or atmospheric concentrations of greenhouse gases. Figures for “carbon equivalents” can be converted to “carbon dioxide equivalents” by multiplying by 44/12 to take account of the different molecular weights. Carbon equivalents can be a more meaningful term when considering carbon not held in the form of CO2, such as coal. However, the IPCC generally uses “carbon dioxide equivalents”.

When referring to greenhouse gas emissions, “carbon dioxide equivalent” refers to the amount of carbon dioxide that would give the same warming effect as the effect of the greenhouse gas or greenhouse gases being emitted. It is normally used when attributing aggregate emissions from a particular source over a specified timeframe. It is used in this way at national and international levels to account for greenhouse emissions and reductions over time. Article 3 of the Kyoto Protocol states targets for emissions reductions in terms of “aggregate anthropogenic carbon dioxide equivalent emissions of the greenhouse gases listed in Annex A.” Using this approach, Australia’s net greenhouse gas emissions across all sectors in 2004 totalled 564.7 million tonnes of carbon dioxide equivalent. The expected carbon dioxide equivalent emissions from burning different fuels can also be calculated using a standard methodology (see http://www.climatechange.gov.au/workbook/pubs/workbook-feb2008.pdf).

When referring to atmospheric concentrations of greenhouse gases, “carbon dioxide equivalent” refers to the concentration of carbon dioxide that would give the same warming effect as the collective effect of all of the greenhouse gases in the atmosphere. Put in a more technical way, this means the atmospheric concentration of carbon dioxide that gives a radiative forcing equal to the sum of the forcings from all of the individual greenhouse gas in the atmosphere.

Houghton (2004: 259) explains that when converting from carbon dioxide only concentrations to carbon dioxide equivalent concentrations, the amount that needs to be added varies with different concentrations of greenhouse gases as the relationship between radiative forcing and concentration is non-linear. For example, setting stabilisation targets of atmospheric carbon dioxide at 450 or 550 ppm would become about 520 or 640 ppm carbon dioxide equivalents, respectively, due to the additional warming effect of other greenhouse gases. Stern (2007) used the term in this manner. These approaches exclude the cooling effect of aerosols.

However, the use of this term is not uniform when discussing stabilisation targets as some authors define carbon dioxide equivalent concentrations as the net forcing of all anthropogenic radiative forcing agents including greenhouse gases, tropospheric ozone, and aerosols but not natural forcings. Hare and Meinshausen (2006) is an example of this approach. The inclusion of aerosols alters the meaning considerably. As noted earlier, the IPCC’s latest report indicates that the current radiative forcing of non-carbon dioxide greenhouse gases and aerosols effectively cancel each other, so that the net effect of all radiative forcing components is currently roughly equal to the effect of carbon dioxide alone. However, this offsetting effect is unlikely to remain in the future as improved pollution controls are expected to significantly reduce the cooling effect of aerosols over the course of coming decades: Meinshausen et al (2006).

With this context explained, it is understandable why Hansen et al (2008) prefer to use CO2 only targets and avoid the use of CO2-eq targets but for non-climate scientists (such as myself) we have to largely work with the approach adopted by the IPCC and international framework so we cannot avoid using CO2-eq. It is important to understand exactly what people mean when they refer to the term. I look forward to Barry’s explanation about it.

References:

Hansen et al (2008) “Target CO2 – Where should humanity aim?” (in review – see draft at http://arxiv.org/abs/0804.1126).

Hare B and Meinshausen M, “How much warming are we committed to and how much can be avoided?” (2006) 75 Climatic Change 111.

Houghton J (2004), Global Warming: The Complete Briefing (3rd ed, Cambridge University Press, Cambridge)

IPCC (2007), Climate change 2007: Mitigation. Contribution of Working group III to the Fourth Assessment Report of the IPCC (Cambridge University Press, Cambridge), http://www.ipcc.ch/ipccreports/ar4-wg3.htm

Meinshausen M, Hare B, Wigley TML, van Vuuren D, den Elsen MGJ, and Swart R (2006), “Multi-gas emissions pathways to meet climate targets” 75 Climatic Change 151.

Stern N (2007), The Stern Review on the Economics of Climate Change (Cambridge University Press, Cambrige).

Neither Barry, Peter or myself are
suggesting that we should co-opt CCS design engineers or solar
panel engineers for these tasks, we are not proposing any reduction
in efforts to control CO2. Our proposal is simply that people should change their diet to reduce its forcing footprint.

The social impact
on livestock industries would be large, but the social impacts of
larger hurricanes or longer El-Ninos would be far greater.
In any event, these industries already have massive adverse
social impacts
throughout the community. 1 million of the current Australian
population will get colorectal cancer in their lives and about
500,000 of those will be caused by pig, sheep and cattle meat. That
estimate is based on the consensus scientific view of the 150+ authors
of the World Cancer Research Fund 2007 report (rather similar in
nature to the IPCC AR4) and uses calculations of Prof Graham
Giles of Cancer Council Victoria based on their research cohort of
about 37000 Victorians and assuming that people cut back
to one red meat meal per week. So when you think about the impact on
the livestock sector, make sure you balance this with 500,000 fewer
colorectal cancer cases … and that’s just for starters… there is
also heart disease and erectile disfunction to consider … not
to mention the biodiversity impacts of cattle production.

You are correct not to imply economists typically take a laissez-faire attitude to greenhouse gas mitigation. Any economist knows sometimes markets work and sometimes they don’t. Anyone who doesn’t know what market failure is, and doesn’t understand why unrestrainted greenhouse gas emissions are a classsic example of it, doesn’t know much about economics.

I don’t notice many economists sticking their heads in the sand on this issue.

Garnaut is the obvious example of someone taking an orthodox approach to addressing market failure.

Here is another, one you might normally associate with the leave-it-to-the-market philosophy, John Hewson:

“What I would hope, I guess, is that Turnbull should take a harder line on climate change. The suggestion from Garnaut that we can start softly, softly, with 10 or 15 per cent for his target in 2020 is nonsense, against the sort of targets Australia has to meet by 2050. In those terms, I think Turnbull should be taking a harder line, pushing Rudd to do more, setting a high jump bar if you like, against which Rudd will be measured and they would have more significant consequences for business.”

It’s in an interview at:

http://www.businessspectator.com.au/bs.nsf/Article/Hewson-JJ27E?OpenDocument&src=sph

Gaz.

I didn’t intend to blanket all, or indeed many at all, economists in my comment.

I did refer to the “denialists’ laissez faire economic approach”, and in doing so I was speaking of (generally non-economist) deniers of AGW who argue that leaving solutions to an unregulated market is the best answer if warming does actually exist. My reference to the last several days of stock market activity simply reflected that much of the current credit crunch seems to stem from the Bush administration’s enthusiastic laissez faire deregulation that is in line with this ‘leave-it-to-the-free-market’ thinking.

I think that we would both agree that this would not help with successfully mitigating AGW.

Emission-equivalence (in mass of CO2-e per unit time — e.g. Mt CO2-e per year) is defined in terms of the cumulative radiative forcing over some time horizon, taking into account the natural loss of the gas from the atmosphere. Usually the time horizon is taken as 100 years. This is the definition that is used for the National Inventories and the Kyoto Protocol (and most other analysis, e.g. Garnaut). My own view is that emission-equivalence is really just a summary statistic — certainly you can’t use it in climate modelling. Russell, Singer and Brook argue for using a shorter time horizon. I have two problems with this:
(i) moving towards stabilisation reqires using a longer time horizon; (ii) I think their justification of short-term fixes to avoid “tipping points” is weak — there is most likely a sequence of tipping points to be avoided and in the case of arctic summers being ice-free, the time of the “tipping point” is more likely 2000 (i.e now too late) rather than 2015.

Of course, countries with economies built around coal will go out of their way to ignore this, but it is one of those insights that is so blindingly obviously correct that it’s a marvel that nobody thought of it before — probably they did. Spencer Weart will probably come up with someone who worked this out in 1897!

For example, with peak emissions occurring in 2015, a target of 450 ppm CO2e (we really need to get clear on this CO2 vs CO2e thing) requires 6.5% annual reductions in energy and process emissions.

As a real-world policy, that might not be the best way to proceed, since it requires the biggest absolute reductions immediately after the peak. But there’s no need to assume constant annual reductions. For example, they could follow a Bell curve shape, with the early reductions starting small, the rate of reduction then rising to its maximum, and then tailing off again as an asymptotically safe level of emissions is reached.

I find that this way of thinking can take you a long way towards imagining realistic emissions trajectories. Thus, the 450 scenario outlined by the IEA works a bit like the “stabilization wedge game”, with some of the reduction coming from renewables, some from nuclear, some from carbon capture, and some from efficiency. Throw in that famous I=PAT equation (Impact = Population x Affluence x Technology), the idea that economic growth = growth in energy use x growth in energy efficiency, ideas about differentiated responsibility… and you can pretty much construct your own blueprint for the content of a Copenhagen 2009 agreement, even a 350-compliant one.

http://www.xenomed.com/forums/general-talks/37105-world-s-fattest-man.html