The Self-Regulation Of The Boreal Forest Tree Line – Another Climate Issue That Was Inadequately Examined In The 2007 IPCC Reports

In 1995, we published the paper

Pielke, R.A. and P.L. Vidale, 1995: The boreal forest and the polar front.  J. Geophys. Res., 100, 25755-25758 [see also]

Thanks to Marc Morano of Climate Depot we have been alerted to a new study which provides further confirmation of the role of the boundary between the boreal forest and adjacent tundra to the north as a self-regulation on the tree line. Marc’s post is at

Arctic treeline advance not as fast as previously believed, finds study by Cambridge University

and refers to the Alaska Dispatch article

Arctic treeline advance not as fast as previously believed

The news article starts with the text [highlight added]

A study released this month by Cambridge University indicates the advance of the treeline in the Arctic is moving slower than previously predicted.

The study, which was released March 17 by Gareth Rees, a researcher with the university’s Scott Polar Research Institute, says the relationship between climate change and tree growth is more complicated than initially thought.

“To generalize our results, the tree line is definitely moving north on average but we do not see any evidence for rates as big as 2 kilometers per year anywhere along the Arctic rim,” he said in a news release. “Where we have the most detailed information, our results suggest that a rate of around 100 meters per year is more realistic. In some places, the tree line is actually moving south. The predictions of a loss of 40 percent of the tundra by the end of the century is probably far too alarming.”

The  Pielke and Vidale 1995 paper provides a reason for this limited motion. The abstract reads

The analysis presented in this paper suggests that the larger heating over the boreal forest in the spring and summer, as   contrasted with weaker heating over the adjacent tundra, results in a preferred position of the polar front along the northern edge of the boreal forest. This positioning is well documented in the literature (see, for example, Bryson, 1966; Barry and Hare, 1974; Kreps and Barry, 1970). This heating results from the lower albedo of the boreal forest which is not compensated by an increase in transpiration, even with the larger leaf area index of the forest. The warmer temperatures are mixed upward by the deep boundary layer over the forest and mesoscale circulations which result from the patchiness of heating associated with the heterogeneous landscapes of the forest. Thus in contrast to previous assumptions in which the arctic front position in the summer determines the northern limit of the boreal tree line, our study suggests the boreal forest itself significantly influences the preferred position of the front. This conclusion reinforces the findings of Bonan et al. (1992) and Foley et al. (1994) on the important role of boreal forest-tundra interactions with climate.

The observed limited movement of the boreal tree line is yet another example of the failure of the IPCC and other such climate assessments to recognize important climate feedbacks in the dynamics of the climate system.

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