The UN Framework Convention on Climate Change (FCCC) calls for a "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system." That level is nowhere defined, however, nor is the definition addressed in any of the reports of the UN Intergovernmental Panel on Climate Change [IPCC, 1996]. A reasonable interpretation might be that "dangerous" refers to the stability of the climate system rather than to a simple warming. For example, could higher GH gas (mainly CO2) concentrations produce a sudden, major change in the state of the climate?

Without knowing what level is "dangerous," one cannot define the goal of the FCCC: the present level, or a lower level, or perhaps a higher level. In the absence of such information, it would seem premature to set up mandatory targets on CO2 emissions.

Recently, Azar and Rodhe [1997] have attempted to define a CO2 target level. They conclude that the present level (350 ppmv) or higher ones are dangerous; presumably, lower levels are not. But the analysis to back up the conclusion is inadequate. The authors simply accept that a temperature rise of 2°C or higher is dangerous because it is "considered to be high risk by the Stockholm Environment Institute." Even more questionable is their claim that maintaining the present CO2 level can produce a temperature increase of over 2°C. (The range they show is from 0.9 to 2.7°C.) On the basis of IPCC estimates, they then conclude that annual CO2 emissions must be reduced by 50 percent from present values--worldwide.

1) It should be noted, first of all, that temperatures have varied by more than 3°C in the last 2500 years [Keigwin, 1996], i.e. within recorded history, without leading to climate catastrophes. Some of the changes have been more rapid than 0.25°C per decade, faster even than projected by the IPCC. [See Fig. 1] Even though this particular temperature record came from an ocean core at one location, an independent investigation documents abrupt changes in the early to mid-Holocene at the equator and both poles, i.e. globally [Stager and Mayewski, 1997].]

2) The temperature increases suggested by Azar and Rodhe [1997] for present CO2 levels are wildly out of line with observations; satellites and balloon-borne radiosondes show no warming whatsoever [Spencer and Christy, 1992].

3) One should not rule out the possibility that a higher CO2 level may be less dangerous to the climate system than a lower one. Observations suggest that climate instability has been greater during the extremely low CO2 values of the Ice Ages (< 200 ppmv) than during the Holocene (< 280 ppmv). For example, Stager and Mayewski [1997] point out that the warmer Holocene was relatively more stable than the late Pleistocene. Although abrupt changes occurred in global climate around 8,000 years ago, the fluctuations experienced during the last Ice Age were even greater. A recent review confirms both the climate instability of the Holocene and the even greater variability of the last glacial period [deMenocal and Bond, 1997].

I conclude, therefore, that one cannot argue a priori that higher concentrations of GH gases are "dangerous" to the climate system. More likely, the opposite is true.

S. Fred Singer, Ph.D.
The Science & Environmental Policy Project
Fairfax, VA.

References:

Azar, C., and H. Rodhe, 1997: "Targets for Stabilization of Atmospheric CO2." Science, 276, 1818--1819.

deMenocal, P., and G. Bond, 1997: "Holocene Climate Less Stable Than Previously Thought." Eos Trans. Am. Geophys. Un., 447-454, October 14.

IPCC WGI, 1996: "Climate Change 1995: The Science of Climate Change," J.T. Houghton, L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg and K. Maskell (eds.). Cambridge University Press, Cambridge, UK.

Keigwin, L.D., 1996: "The Little Ice Age and Medieval Warm period in the Sargasso Sea." Science, 274, 1504-1508.

Spencer, R.W., and J.R. Christy, 1992: "Precision and Radiosonde Validation of Satellite Gridpoint Temperature Anomalies. Part II: A Tropospheric Retrieval and Trends during 1979-90." J. Clim., 5, 858-866.

Stager, J.C., and P.A. Mayewski, 1997: "Abrupt Early to Mid-Holocene Climatic Transition Registered at the Equator and the Poles." Science, 276, 1834--1836.

Figure 1: Detailed temperature variations of the past 3,000 years, as determined from ocean sediment studies [Keigwin, 1996]. Note the rapid variations, as well as the much warmer temperatures that existed 2,500 years ago.

Comment and Reply
E O S , Transactions, American Geophysical Union Volume 79, page 188, April 14,1998

Comment

In a recent Forum piece that discusses climate variability (Eos, December 16, 1997), S. F. Singer claims that "a higher CO2 level may be less dangerous to the climate system than a lower one." The basis for this reasoning is the observation that during the last Ice Age, CO2 levels (200 ppmV) were lower than pre-Industrial Revolution Holocene levels (280 ppmV, yet the climate system was apparently more unstable than during the Holocene.

Singer neglects to add that, in addition to CO2, other Ice Age global boundary conditions were very different from today's, notably larger continental ice sheets in the Northern Hemisphere, higher levels of aerosols, and colder sea-surface temperatures. Climatic variations associated with these boundary conditions are not completely understood, but clearly singling out CO2 grossly oversimplifies the complexity of the climate system and the underlying causes of climate variability.

Singer also overlooks the Younger Dryas cooling event which, as apparently the largest climate jump recorded in the Greenland ice cores, occurred during the rapid glacial-interglacial rise in CO2 levels, along with a younger (8200 yr B.P.) cooling event of about half the amplitude of the Younger Dryas, which occurred after Holocene CO2 levels were reached. These and other known changes in climates of the past give no confidence to the argument that rising CO2 levels will stabilize climate in the future.

Indeed, if past behavior of CO2and climate hold any predictive value, as suggested by Singer, then the correlation of large instabilities to rapidly changing CO2 levels may be alarming in light of future increases in greenhouse-gas concentrations.
Richard B. Alley, Department of Geosciences and Earth System Science Center, Pennsylvania State University, University Park, USA; Patrick J. Bartlein, Department of Geography, University of Oregon, Eugene, USA; Peter U. Clark, Department of Geosciences, Oregon State University, Coroallis, USA; Steven W. Hostetler, U.S. Geological Survey, Corvallis, Ore., USA; and Alan C Mix, College of Oceanic and Atmospheric Sciences, Oregon State University, Coruallis, USA

Reply

I welcome the substantive comments by Alley et aft They are well taken, but they miss my real point-as did the earlier comment by Dickinson [ 1997]. Briefly stated: Will a higher level of Condor more importantly, a warmer climate-produce a less stable climate or lead to the opposite result? As far as I can tell, this is very much an open question. Yet this crucial issue determines the goal of the Global Climate Treaty and its attempted implementation by the 1997 Kyoto Protocol.

My forum article [Singer, 1997a] was prompted by the entirely spurious claims [Rodhe and Azar, 1997] that 1) the present level of CO2 would lead to a warming of 2°C, and that 2) an obscure report by the Stockholm Environment Institute-likely a self-reference-had demonstrated that such a condition, that is, the present CO2 level, would be "dangerous to the climate system" (in the sense of Article 2 of the Climate Treaty); one must therefore reduce the concentration by reducing CO2 emissions by 6080%. But, as I pointed out, there is sufficient evidence in the historic record for warm periods that exceeded the 2°C level without having "endangered" the climate system [Singer 1 997b] .

While the goal of the Climate Treaty remains scientifically undefined, politicians are charging ahead with economically ruinous schemes to stabilize the concentration of selected greenhouse gases, for example CO2 but not methane, without knowing what the goal should be-or, indeed, in which direction to go. At the 1992 Rio Conference, the goal for CO2 appeared to be the 19901evel, about 350 ppmv. At Kyoto, the politically expedient level seemed to have advanced to about 560 ppmv, twice the pre-industrial value. (I admire the principled position by the Greenpeace representative at the IPCC meeting in Madrid in November 1995, who called for a return to the pre-industrial level of 280 ppmv. Unfortunately, this requires negative emission rates of CO2.) But if the goal of the Treaty is to be determined by politics rather than by science, let's be honest about the real motives of the promoters of the Kyoto Protocol (be it the elimination of fossil fuels, or whatever) and not use climate science as an excuse.-S. Fred Singer, The Science & Environmental Policy Project, Fairfax, Va., USA

References

Azar, C., and H. Rodhe, Targets for stabilization of atmospheric C02, Science, 276, 1818-1819, 1997.
Dickinson, R., Time to act is now, Eos Trans. AGU, 78. 584. 1997.
Singer, S. F., Unknowns about climate variability render treaty targets premature Eos, Trans. ACU, 78. 584, 1997a.
Singer, S. F., Hot Talk, Cold Science: Global Warming's Unfinished Debate, The Independent Institute, Oakland, Calif. 1 997b.