Global Warming: is the True Story Being Told?

The climate change debate has a number of interesting points that the average person may not know about. Paleo-climate reconstruction data is one of the points hotly debated. This field of science uses proxy data to determine or reconstruct past temperatures. Cores of sea sediment, glacial ice, cave formations (stalactites and stalagmites) and tree ring growth rate are some of the more common proxies used. One of the most commonly questioned is the tree ring temperature proxy.

Each year of its life a tree adds an annual ring as most of you will remember from grade school. The width of the rings varies, depending on the growing conditions of that year. Thicker rings indicate faster annual growth and thinner rings the reverse. The assumption is that thicker rings are associated with warmer average summer temperatures.

There are factors that affect tree growth other than temperature. Rainfall, available nutrients and pests are import influences on tree growth. For a tree to be a good proxy for temperature, the factors other than temperature must remain fairly stable over the life of the tree. That is the problem with this proxy, determining if factors other than temperature had significant impact on the tree's growth.

This year the weather patterns in the western US provide an excellent example of how temperature and tree growth can be confusing. The western US had warmer than average summer temperatures and much less than average rainfall. The drought conditions decreased the growth rate of the trees. Drought may or may not be associated with warmer than normal temperatures.

The wild fires this year also are an example of an inverse temperature tree growth rate relationship. While fire does destroy trees of course, it releases nutrients that extend the growing season and improving growth rates of trees near but not impacted by the fire. Trees damaged but not destroyed by the fire are more susceptible to insect and other pests that can reduce growth rate.

To have a proper correlation between temperature and growth rate the location of the trees has to have stable conditions. To meet this requirement alpine and sub-arctic locations are assumed to be more stable. In general this would be a valid assumption. There are exceptions. The bristlecone pine may very well be one of the exceptions.

The bristlecone pine is a very long lived tree (four to five thousand years in some cases) implying it would be an ideal candidate for long term temperature proxies. The bristlecone pines grow in the Sierra Nevada mountains in California and Nevada, an area prone to drought during warmer temperatures. While snow melt is assumed to provide relatively stable water supply, this may not be the case for prolonged warmer weather trends.

Other trees used for proxies, Larch trees found in sub-arctic Eurasia, have long life spans (one thousand years or so). While there is the potential for drought in the area the larch trees are found, the sub-arctic location would be less prone to drought conditions. In this link , Olga V. Sidorova, Mukhtar M. Naurzbaev, Eugene A. Vaganov (SNV) V.N. Sukachev Institute of Forest SB RAS, Krasnoyarsk, Russia, detail their study of the larch trees in a very clear, easily readable manner. Near the end they compare their results to the Mann et al study that includes the bristlecone pine proxy. Their conclusion is significantly different from the Mann conclusion specifically related to the Medieval Warming Period (MWP) and current temperatures not being as warm as the MWP. The larch tree data compiled by SNV is not included in the multi-proxy reconstruction of temperatures for the past two thousand years.

The omission of the SNV study is a point of great debate in the climate change issue as is the inclusion of the bristlecone pine study. With accusations of cherry picking data flying from both sides of the debate, it would seem reasonable that the statistical validity of all available proxies would be considered and valid proxies included in a do over of the historical temperature reconstruction. Politics and egos seem to be butting heads with the science of climatology.

Given the importance of the global warming situation I find it shocking the seemingly valid scientific data is not included in temperature reconstructions without clear reason for the omissions. All valid data must be included if an accurate picture of past climate is to be painted.

This article is submitted for non-payment and has not been reviewed by Associated Content. Associated Content does not endorse the views of this author. The author is not a scientist and simply wishes that more people become aware of legitimate issues involved in the climate change debate.

Photograph provided courtesy of Phillip Greenspun