December 9, 2005

Natural Warming Larger Than Thought?

Below are some observations found in a couple of recent journal articles that have received little attention—hmm, we wonder why?

The first observation was made by a team of paleoclimatologists led by Jan Esper in a viewpoint paper entitled “Climate: past ranges and future changes,” published in Quaternary Science Reviews. Esper and colleagues examined the amplitude of the temperature variations that have been reported for earth’s temperature during the past millennium. These include studies from the by-now familiar names of Mann, Moberg, Jones, Esper and Briffa.

Esper et al. summarize their effort:

Comparison of large-scale temperature reconstructions over the past millennium reveals agreement on major climatic episodes, but substantial divergence in the reconstructed (absolute) temperature amplitude. We here detail several research priorities to overcome this ‘amplitude desideratum’, and discuss the relevance of this effort for the prediction of future temperature changes and the meaning of the Kyoto Protocol.

In particular, they conclude:

So, what would it mean, if the reconstructions indicate a larger (Esper et al., 2002; Pollack and Smerdon, 2004; Moberg et al., 2005) or smaller (Jones et al., 1998; Mann et al., 1999) temperature amplitude? We suggest that the former situation, i.e. enhanced variability during pre-industrial times, would result in a redistribution of weight towards the role on natural factors in forcing temperature changes, thereby relatively devaluing the impact on anthropogenic emissions and affecting future predicted scenarios. If that turns out to be the case, agreements such as the Kyoto protocol that intend to reduce emissions of anthropogenic greenhouse gases, would be less effective than thought.

Well, since we already know that the Kyoto protocol is ineffective as it is, Esper doesn’t add much insight there. But, it sure seems that Esper and colleagues are making the case that natural variability may have had a larger impact (and thus the human impact has been smaller) on the temperature trends during the past century or so that is generally realized.

The second observation on the relative impact of man vs. nature on temperature is given by United States Geological Survey scientists Timothy Cohn and Harry Lins in a paper appearing in Geophysical Research Letters, entitled “Nature’s style: Naturally trendy.” In this rather technical and mathematical work, the authors examine the role of long-term persistence in the temperature record and how it affects the significance of the temporal trend often drawn through the earth’s recent temperature history. Cohn and Lins conclude that the very real possibility that the natural climate system contains a high degree of long-term persistence means that the degree to which the temperature rise during the past century is of a natural vs. anthropogenic cause cannot clearly be determined. Specifically, they wrote:

These findings have implications for both science and public policy. For example, with respect to temperature data, there is overwhelming evidence that the planet has warmed during the past century. But could this warming be due to natural dynamics? Given what we know about the complexity, long-term persistence, and non-linearity of the climate system, it seems the answer might be yes. Finally, that reported trends are real yet insignificant indicates a worrisome possibility: Natural climate excursions may be much larger than we imagine. So large, perhaps, that they render insignificant the changes, human-induced or otherwise, observed during the past century.

Apparently, the existence of such scientists with such opinions is lost on all those folks proclaiming the “science is settled,” such as Bill Clinton, who, in his remarks made to rally the troops at the closing of the U. N. climate meetings in Montreal said, “There’s no longer any serious doubt that climate change is real, accelerating and caused by human activities.” Bill, read the literature.


Cohn, T. A., and Lins, H. F., 2005. Nature’s style: Naturally trendy. Geophysical Research Letters, 32, doi:10.1029/2005GL024476.

Esper, J., et al., 2005. Climate: past ranges and future changes. Quaternary Science Reviews, 24, 2164-2166.

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