Climate Change and Positive Feedback Mechanisms — Russia’s Northern Forest Composition Is Changing to More Warmth-Tolerant, Needle-Retaining Species, thereby Increasing Ground Heat Retention

27 March 2011

Positive feedback hidden in the mix

Unanticipated positive feedback has a way of escalating change in attention-getting ways. Here’s one from Russia’s northern forests:

The Northern Hemisphere's boreal forests, particularly the Siberian boreal forest, may have a strong effect on Earth's climate through changes in dominant vegetation and associated regional surface albedo.

We show that warmer climate will likely convert Siberia's deciduous larch (Larix spp.) to evergreen conifer forests, and thus decrease regional surface albedo.

© 2011 Jacquelyn Kremper Shuman, Herman Henry Shugart and Thomas Liam O'Halloran, Sensitivity of Siberian Larch forests to climate change, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02417.x (accepted article, 2011)

The boreal forest albedo model is based on documented forest composition changes

The University of Virginia, with whom two of the authors are associated, explained that Russia’s boreal forest is the size of the U.S.’s lower 48 states. Climate warming and forest compositional changes have been documented there for decades.

Shuman et al.’s mathematical model takes these changes into account:

"We've identified that the boreal forest, particularly in Siberia, is converting from predominantly needle-shedding larch trees to evergreen conifers in response to warming climate," said the study's lead author, Jacquelyn Shuman . . . .

Larch trees drop their needles in the fall, allowing the vast snow-covered ground surface of winter to reflect sunlight and heat back into space. This helps keep the climate in the region very cold.

But evergreen conifers, such as spruce and [fir], retain their needles year round. These trees absorb sunlight, which causes ground-level heat retention.

This creates ideal conditions for the proliferation of evergreens, to the detriment of the leaf-dropping larches. The result is a northward progression of evergreens and a farther-northward retreat by the larch forests.

The researchers used a climate model to assess what would happen if evergreens continued to expand their range farther north and larch species declined.

The "positive feedback" cycle of warming promoting warming showed an increase of absorbed surface warming.

Albedo is important

Albedo is a measure of the fraction of solar radiation reflected from a surface. Perfect reflectivity would be 100 percent (or simply “1”). In the real world, everything is less than 1.

You can find a chart comparing reflectivities here, at the Encyclopedia of Earth.

Obviously as the Earth’s ice covering decreases, albedo declines. Similarly, as dark forest begins covering previously lighter surfaces, if only for part of the year, reflectivity will also decline.

Presumably, all other variables held static, reduced reflectivity means that the Earth warms.

But reality may not be that simple

Albedo is only one of many variables. The others will not stay static. They may change in ways that return to change albedo.

For example, we cannot be sure that increased heat retention will not result in more cloud formation in some regions. And with them, a local or regional counter-mechanism that offsets some of the effects of reduced albedo’s warming effect. How that would integrate into the climate as a totality is a still deeper question.

The moral? — fast-moving uncertainties in the midst of probable unpleasantnesses

Climate is changing, probably with a rapidity that human beings can take credit for. But its overall effects are difficult to anticipate, regionally and globally.

Nevertheless, these weather/climate hanges are beginning to look as if they are going to arrive more quickly and impressively than concerned people anticipated just a few years ago.

Some governments may come to think that geoengineering is not a disproportionate response.

Can you imagine the international tensions that might result from conflicting views regarding climate manipulation?

PeteFree.com

Climate Change and Positive Feedback Mechanisms — Russia’s Northern Forest Composition Is Changing to More Warmth-Tolerant, Needle-Retaining Species, thereby Increasing Ground Heat Retention