Despite record lows in solar magnetic activity, thought to influence the climate, trends continue to point to a clear rise in temperatures worldwide. This is reflected by increased melting and other significant changes.
Now one of the more cohesive studies to date, published by Penn State's Earth System Science Center, has offered up a factual analysis of exactly how much warming is occurring. Rather than focus on creative modeling often considered a refuge of global warming skeptics and alarmists alike, Penn state instead analyzed historic and contemporary data.
It found that the last 10 years for the Northern Hemisphere were the hottest in 1,300 years. They also asserted that if more controversial tree ring data were used, this range could be extended to 1,700 years, but the tree ring data is for the first time unnecessary, eliminating much controversy.
Michael Mann, associate professor of meteorology and geosciences and director of Penn State's Earth System Science Center, states, "Some have argued that tree-ring data is unacceptable for this type of study. Now we can eliminate tree rings and still have enough data from other so-called 'proxies' to derive a long-term Northern Hemisphere temperature record."
Among the extensive information used in the analysis were marine and lake sediment cores, ice cores, and coral cores.
The research is available in the Sept. 2 issue of Proceedings of the National Academy of Sciences (PNAS). Mr. Mann describes, "We looked at a much expanded database and our methods are more sophisticated than those used previously. Conclusions are less definitive for the Southern Hemisphere and globe, which we attribute to larger uncertainties arising from the sparser available proxy data in the Southern Hemisphere."
Part of the paper's strength derives from its veritable who's who of climatologists and leading scientists -- Mann; Ray Bradley, university distinguished professor, geosciences and director, Climate System Research Center, University of Massachusetts; Malcolm Hughes, regents' professor, and Fenbiao Ni, research associate, the Laboratory of Tree Ring Research, University of Arizona; Zhihua Zhang and Sonya Miller, research associates, meteorology, Penn State; and Scott Rutherford, assistant professor, environmental sciences, Roger Williams University
The study took place based on a National Research Council paper, "Surface Temperature Reconstructions for the Last 2,000 Years", which called for a fresh analysis using new techniques and verified climate record from Mann's influential 1990s paper on the topic. In the 1990s using the most advanced techniques, the climate record could be traced back 1,000 years using the most advanced techniques, and farther using the contested tree ring data. Today, the climate record can be traced back over 1,300 years to 700 A.D. thanks to more advanced techniques. If the debated tree ring approach was brought in, scientists could detail global temperatures all the way back to 300 A.D.
One of the key reason why the study is avoiding the primary use of tree ring data was because of the so-called "segment length curse". As trees age, their rings, typically dependent on temperature, experience a general shrinking. This shrinking must be adjusted to accurately read temperatures, thus tree ring data is expected to be less accurate than other methods. Fortunately, climatologists are doing fine without it.
Mr. Mann details, "Ten years ago, we could not simply eliminate all the tree-ring data from our network because we did not have enough other proxy climate records to piece together a reliable global record. With the considerably expanded networks of data now available, we can indeed obtain a reliable long-term record without using tree rings."
The study provides perhaps the most conclusive proof to date that the world has been experiencing anomalous warming. With sun activity thought to be on the decline, this leaves human influence and other remaining potential causes as likely candidates for the affecting agent.