Monckton Myth #5: Dangerous Warming

In his recent response to Steketee's article in The Australian, Monckton's argument #7 reads as follows:

the IPCC’s current thinking is that up to 2° of warming compared with the present would be harmless and even beneficial. Since far greater temperatures than this have been the rule on Earth for most of the past 600 million years, there is no sound scientific basis for the assumption that “significant environmental and economic damage” would result from so small an additional warming. However, significant economic damage is already resulting from the costly but pointlessly Canute-like attempts governments to try to make “global warming” go away.

Chris, I Have a Feeling We're Not in the Paleozoic Anymore

Monckton's reference to the past 600 million years is simply not relevant, because millions of years ago ecosystems and the species living in them were radically different from those today.  We cannot infer the amount of environmental and economic damage we will experience based on the state of the climate 600 million years ago.

What Does the IPCC Say?

Monckton's statement that the IPCC concluded that up to 2°C warming compared to the present would be harmless or beneficial is simply false.  Here is the actual IPCC conclusion on the subject.

Limited and early analytical results from integrated analyses of the costs and benefits of mitigation indicate that they are broadly comparable in magnitude, but do not as yet permit an unambiguous determination of an emissions pathway or stabilisation level where benefits exceed costs.

There have been numerous studies pertaining to ecological and economic costs and benefits of additional global warming since the IPCC Fourth Assessment Report, (AR4) and these will be the subject of a future Monckton Myth.  However, Monckton is incorrect that the IPCC has concluded that up to 2°C warming from current levels will be harmless or beneficial - the IPCC did not quantify a specific level at which climate change damages exceed the benefits.  The IPCC did conclude that this level of warming will have some serious negative impacts:

Approximately 20 to 30% of plant and animal species assessed so far (in an unbiased sample) are likely to be at increasingly high risk of extinction as global mean temperatures exceed a warming of 2 to 3°C above preindustrial levels (medium confidence).
Figure 4.4 from Chapter 4 of Working Group (WG) II of the IPCC AR4 report illustrates some of the risks to various ecosystems in a warmer world (cilck here for a larger version):

Figure 1: Compendium of projected risks due to critical climate change impacts on ecosystems for different levels of global mean annual temperature rise, ?T, relative to pre-industrial climate.

As you can see, there are numerous adverse risks to ecosystems for a warming of 2-3°C above pre-industrial levels.  Of course, impacts to ecosystems are only one piece of the puzzle when trying to determine when the negatives will outweigh the positives.  In chapter 5 of WG II, the IPCC concludes that for a small amount of warming, crop yields may increase slightly in mid- and high-latitude regions, but will decrease in low-latitude regions (especially the tropics), increasing the risk of hunger.

In short, the IPCC concludes that small amounts of warming will be a mixed bag, and contrary to Monckton's claims, does not set a level at which the net effects of warming will switch from beneficial to detrimental.  However, Stetekee is correct that other groups have set 2°C of warming above pre-industrial levels as the danger limit.

The 2°C Danger Limit

The history of and reasoning behind the 2°C danger limit is discussed in a paper by Carlo and Julia Jaeger (2010).  As they discuss, the limit was first suggested by Yale economist William Nordhaus in 1975, who made the following argument:

As a first approximation, it seems reasonable to argue that the climatic effects of carbon dioxide should be kept within the normal range of long-term climatic variation. According to most sources the range of variation between distinct climatic regimes is in the order of ±5°C, and at the present time the global climate is at the high end of this range. If there were global temperatures more than 2° or 3°  above the current average temperature, this would take the climate outside of the range of observations which have been made over the last several hundred thousand years.

The same 2°C target was taken up by the WMO/ICSU/UNEP Advisory Group on Greenhouse Gases in 1990, which argued that a 2°C increase was ‘‘an upper limit beyond which the risks of grave damage to ecosystems, and of nonlinear responses, are expected to increase rapidly.’’   In 1995, the German Advisory Council on Global Change supported both of these lines of thinking. It considered the late Quaternary, (the period of the last 800,000 years), and claimed:

This geological epoch has shaped our present-day environment, with the lowest temperatures occurring in the last ice age (mean minimum around 10.4°C) and the highest temperatures during the last interglacial period (mean maximum around 16.1°C).  If this temperature range is exceeded in either direction, dramatic changes in the composition and function of today’s ecosystems can be expected. If we extend the tolerance range by a further 0.5°C at either end, then the tolerable temperature window extends from 9.9 to 16.6°C.  Today’s global mean temperature is around 15.3°C, which means that the temperature span to the tolerable maximum is currently only 1.3°C [2°C above pre-industrial levels].’’

In 1996, the Council of the European Union officially adopted the 2°C target as a standard of climate policy.  The 2003 Assessment of Knowledge on Impacts of Climate Change added further support to the 2°C danger limit in a very detailed report, concluding:

Above 2°C the risks increase very substantially involving potentially large extinctions or even ecosystem collapses, major increases in hunger and water shortage risks as well as socio-economic damages, particularly in developing countries.

An Even Lower Long-Term Target

Hansen et al. (2008) argue that in the long-term, we should aim for an even lower atmospheric greenhouse gas concentration than would result in 2°C of surface warming.

We use paleoclimate data to show that long-term climate has high sensitivity to climate forcings and that the present global mean CO2, 385 ppm, is already in the dangerous zone....Equilibrium sea level rise for today’s 385 ppm CO2 is at least several meters, judging from paleoclimate history....If the present overshoot of this target CO2 [350 ppm, or approximately 1°C above pre-industrial levels] is not brief, there is a possibility of seeding irreversible catastrophic effects.

Danger, Chris Monckton, Danger!

As discussed above, although the IPCC has not established a specific warming target, there is a scientific case to be made for considering 2°C above pre-industrial levels (approximately 1°C above current levels) the 'danger limit' beyond which the risks of significant adverse impacts become too high.

In a later Monckton Myth, we will examine his assertion that the costs of reducing greenhouse gas emissions exceed the costs of adapting to climate change.

Posted by dana1981 on Friday, 21 January, 2011

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