Climate Combinations in the Northern Plains/Rockies

By Lance Olsen, Unfiltered 7-24-07

Climate Combinations
By Lance Olsen

In recent seminars for climate and wildlife researchers, grad students, and representatives of environmental groups, I've tried to spend their afternoons moving fairly quickly through a broad range of peer-reviewed papers for some synthesis of findings that often come rushing past us one by one. I begin with a quick review of four different drivers of climate change, and, near the end, with review of two recent papers indicating a future of forest death.

Four kinds of climate change

Four kinds of climate change that I cover are natural fluctuation,
particle forcing, land-use forcing, and greenhouse forcing. These are not competing explanations of climatic change. They can coincide, and interact, and they can do it in ways that reduce or heighten risk of dangerously rising temperatures.

Everyone has heard of natural fluctuation, a.k.a. natural variability or, alternatively stated, natural cycles. This form of change has affected living systems since long before humans arrived on the scene, and can arise from fluctuation in solar output, volcanic eruption, and other variables including even the wobble of Earth around its axis, but natural fluctuation isn't the only kid on the block.

Particle forcing is less well known beyond the climate sciences. Also called dimming, particle forcing can cool things down, as when a large volcanic eruption fills the atmosphere with particles enough to force incoming solar energy back into space. In that case, a cooling climate would fall into the range of natural fluctuation, not a human forcing of change on our climatic system. But society can force this kind of change by, for example, nuclear war.

Land use forcing refers to change forced on the climate by human uses of the land surface. The classic case is deforestation that triggers drought at downwind locations. But researchers argue that we force change on the climate system via a host of land uses including irrigation and the sprawl of asphalt parking lots, rooftops, and streets. While many of the climatic effects of land use seem local, they can have cumulative effect on regions, continents, or the globe.

Greenhouse forcing is the biggest and most well known climate bully on the block, already forcing consequential change on spaces, species, and systems. The key concern here is the rising global temperatures brought on by our flooding the atmosphere with greenhouse gases, including CO2. And here's where the most dangerous interactions can occur, as for example the same natural fluctuation that elevated atmospheric CO2 to about 1200 ppm during the Eocene now brings some similar ppm to an atmosphere laced with CO2 ppm of human origins. In this scenario, the heat would extinguish species galore, certainly including our own.

Now, while I've seen no reports indicating anything like an imminent repeat of Eocene-like conditions, the risk is that we have set Life up for extreme danger if anything like it comes atop the ppm content of our own making.

Forest death

Two recent papers, when put side by side, point to an extreme scenario for forests even if no natural variable arrives to combine with greenhouse forcing.

In an article published in Proceedings of the National Academy of Sciences, Breshears et al cite evidence that recent drought in the Southwest was not as severe as droughts in the 1930s and 1950s, that those earlier droughts mostly killed trees older than 100 years, but that the recent drought combined with higher temperatures than earlier droughts, qualifying it as a "global change-type" drought , and that the higher temps of this kind of drought killed trees across age-size classes.

That latter finding really caught my eye, because deaths across age-size classes would effectively squelch prospects for the young trees that would make a future forest possible. And because, of course, Rocky Mountain forests are plainly headed into hotter times.

In an article published by Science, Meehl and Tebaldi cite evidence pointing toward increased extremes of heat, longer lasting extremes, more intense ones. These longer, stronger, and more persisting extremes will be influencing everything, including young trees.

So, when I contemplate the Breshears and Meehl papers as a logical pair, I come up with a scenario of repeated death for old and young forests, on a repeat basis, and likely for centuries down the road. What this scenario suggests to me that is logging exec's claims that forests can recover from logging, and environmentalistis' claims that forests can recover from fire are equally relegated to yesterday.

With the Pinus group already on a heat-driven decline (whether by beetle, drought, fire. outright death from heat stress, or combinations of any two) at every latitude in Western North America, from the desert Southwest to
British Columbia, it's become hard to duck the prospect of pine forest dieoff at a continental scale. And the pines aren't the only vulnerable trees in the Rocky Mountains.

Montana native Lance Olsen has followed the evolving science of atmosphere-species relationships since 1972.

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