by Carl Strang
This blog focuses on studies of local natural history, but there is no question that the future of any ongoing story is subject to whatever form climate change may take. Today I share notes from my annual literature review that are particularly relevant to this subject.
McCarthy, James J. 2009. Reflections on: our planet and its life, origins, and futures. Science 326:1646-1655. This is the AAAS presidential address. In it he cites an impressive model and data set showing a tight correlation of global monthly mean temperatures with a combination of 4 factors, each of which contributes significantly to the variation. They are the El Niño-Southern Oscillation (especially responsible for unusually warm or cold years), volcanic aerosols (generally constant but in occasional year-long bouts of low levels producing global temperature dips), solar irradiance (rising and falling on a roughly decade-long cycle) and anthropogenic effects (mainly greenhouse gas emissions, producing an overall strong upward trend over the past 3 decades). He also says that “Demographic studies suggest that because of declining birthrates across much of the developing world, a future doubling of today’s population of 6.8 billion is unlikely. Most projections point to a leveling off of human population at 9 to 11 billion within the next two to three generations.”
Ditlevsen, P. D., and S. J. Johnsen. Tipping points: Early warning and wishful thinking. Geophys. Res. Lett., DOI: 10.1029/2010GL044486
Their studies of sudden episodes of drastic climate change during the ice ages casts a new light on climate change concerns. Earlier research had found that on several occasions, temperature shifts of 10-15 degrees occurred in only one to a few decades during the glacial times. Such shifts between relatively stable climate states then persisted sometimes for hundreds of years. Understanding them requires the inclusion of chaos theory, which makes them essentially impossible to predict given current knowledge. While the authors point out that this is a study of past events rather than the current situation, they also mention that carbon dioxide levels have risen to match those of much warmer global conditions 15 million years ago, and this might influence the system to jump into a different stable state over a very short span of years.
Kitcher, Philip. 2010. The climate change debates. Science 328:1230-1234. This extensive review of a number of recent books on climate change does a good job of bringing out how the debate has taken place, and the various roles taken by authoritative scientists, the media, politicians, business interests, the public, and “obfuscators,” scientists from other fields who have claimed an authority they don’t possess.
Smithsonian Institution (2010, February 2). Forests are growing faster, ecologists discover; Climate change appears to be driving accelerated growth. ScienceDaily. Retrieved February 3, 2010, from http://www.sciencedaily.com /releases/2010/02/100201171641.htm
“For more than 20 years forest ecologist Geoffrey Parker has tracked the growth of 55 stands of mixed hardwood forest plots in Maryland. The plots range in size, and some are as large as 2 acres. Parker’s research is based at the Smithsonian Environmental Research Center, 26 miles east of the nation’s capital.
“Parker’s tree censuses have revealed that the forest is packing on weight at a much faster rate than expected. He and Smithsonian Tropical Research Institute postdoctoral fellow Sean McMahon discovered that, on average, the forest is growing an additional 2 tons per acre annually. That is the equivalent of a tree with a diameter of 2 feet sprouting up over a year…
“During the past 22 years CO2 levels at SERC have risen 12%, the mean temperature has increased by nearly three-tenths of a degree and the growing season has lengthened by 7.8 days. The trees now have more CO2 and an extra week to put on weight. Parker and McMahon suggest that a combination of these three factors has caused the forest’s accelerated biomass gain.”
Stone, Richard. 2010. Home, home outside the range? Science 329:1592-1594. This news-review article describes the debate over whether people should use assisted colonization (the deliberate northward displacement of populations) to help species survive climate change. Opponents cite examples of the problems that arise with introductions of nonnative species. Proponents point to successes that have been achieved with relatively small northward shifts. Conditions under which assisted colonization is called for are being debated and developed.