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Another Global Warming Horror Story Bites the Dust
Putative CO2-induced global warming has long been predicted to turn boreal and tundra biomes into carbon sources extraordinaire.  Until just a few short years ago, it was nearly universally believed that higher soil temperatures would lead to the thawing of extensive regions of permafrost and the exposure and subsequent decomposition of their vast stores of organic matter, thereby releasing the soil's tightly-held carbon and allowing it to make its way back to the atmosphere as CO2, from whence and in which form it originally came.

Associated tendencies for improved soil drainage and increased aridity were also envisioned to help the process along, possibly freeing enough carbon at a sufficiently rapid rate to rival in aggregate the yearly amount of carbon released to the atmosphere as CO2 by all anthropogenic sources combined.  The end result was claimed to be a tremendous positive feedback to the ongoing rise in the air's CO2 content, which would produce a greatly amplified atmospheric greenhouse effect that would lead to catastrophic global warming.  In a slight variation of a well-worn theme, however, the scenario was just too bad to be true.

One of the first cracks in the seemingly sound hypothesis appeared a little over a year ago, when long-term measurements of net ecosystem CO2 exchange in wet-sedge and moist-tussock tundra communities of the Alaskan Arctic indicated they were gradually shifting from being carbon sources to becoming carbon sinks (Oechel et al., 2000).  The ultimate transition occurred between 1992 and 1996, at the apex of a regional warming trend that culminated with the local climate experiencing the highest average summer temperature and surface water deficit of the previous four decades.

How did it happen, this dramatic and unexpected biological transformation?  The answer of the scientists who observed and documented the phenomenon is that it was really nothing special - no more, as they put it, than "a previously undemonstrated capacity for ecosystems to metabolically adjust to long-term changes in climate."

Yes, just as people can change their behavior in response to environmental stimuli, so can plants.  And this simple ecological acclimation process is only one of several such newly-recognized phenomena that have caused scientists to radically revise the way they think about global change in Arctic regions.

The most recent of the still-evolving new work in this area comes from Camill et al. (2001), who studied (1) changes in peat accumulation across a regional gradient of mean annual temperature in Manitoba, Canada, (2) net aboveground primary production and decomposition for major functional plant groups of the region, and (3) soil cores from several frozen and thawed bog sites that were used to determine long-term changes in organic matter accumulation following the thawing of boreal peatlands.

In direct contradiction of earlier thinking on the subject, but in confirmation of the more recent findings of Camill (1999a,b), the authors of the new study discovered that aboveground biomass and decomposition "were more strongly controlled by local succession than regional climate."  In other words, they determined that over a period of several years, natural changes in plant community composition generally "have stronger effects on carbon sequestration than do simple increases in temperature and aridity."  In fact, the authors' core-derived assessments of peat accumulation over the past two centuries demonstrated that rates of biological carbon sequestration can almost double following the melting of permafrost, in harmony with the findings of Robinson and Moore (2000) and Turetsky et al. (2000), who found the rates of organic matter accumulation in other recently-thawed peatlands to rise by 60-72% in newly-warmed climatic regimes.

As seems to be happening in so many other areas of research designed to increase our knowledge of the hypothetical global warming threat, this new evidence from the carbon sequestration front turns the old gloom-and-doom hypothesis on its head.  Rather than adding to the atmosphere's burden of carbon dioxide, warming of earth's permafrost regions would likely end up removing carbon from the air, which would tend to stabilize surface air temperatures and not push them higher.

Thank goodness for scientists willing to challenge even reasonable-sounding theories.

Dr. Sherwood B. Idso Dr. Keith E. Idso

References
Camill, P.  1999a.  Patterns of boreal permafrost peatland vegetation across environmental gradients sensitive to climate warming.  Canadian Journal of Botany 77: 721-733.

Camill, P.  1999b.  Peat accumulation and succession following permafrost thaw in the boreal peatlands of Manitoba, Canada.  Ecoscience 6: 592-602.

Camill, P., Lynch, J.A., Clark, J.S., Adams, J.B. and Jordan, B.  2001.  Changes in biomass, aboveground net primary production, and peat accumulation following permafrost thaw in the boreal peatlands of Manitoba, Canada.  Ecosystems 4: 461-478.

Oechel, W.C., Vourlitis, G.L., Hastings, S.J., Zulueta, R.C., Hinzman, L. and Kane, D.  2000.  Acclimation of ecosystem CO2 exchange in the Alaskan Arctic in response to decadal climate warming.  Nature 406: 978-981.

Robinson, S.D. and Moore, T.R.  2000.  The influence of permafrost and fire upon carbon accumulation in high boreal peatlands, Northwest Territories, Canada.  Arctic, Antarctic and Alpine Research 32: 155-166.

Turetsky, M.R., Wieder, R.K., Williams, C.J, and Vitt, D.H.  2000.  Organic matter accumulation, peat chemistry, and permafrost melting in peatlands of boreal Alberta.  Ecoscience 7: 379-392.