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Climate Change: More Than a 1,000-Year Window on Regional Temperatures

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Herculean effort by scientific community yields new insight on long-term climate trends.

Deducing the long-term changes in atmospheric temperatures is a complicated and difficult undertaking, requiring careful analysis to piece together many, many bits of data from a variety of proxies (such as ice cores, pollen, ocean and lake sediments, tree rings, cave formations, corals) for the temperature at a given location and point in time.

One of the first of such studies (and arguably one of the most controversial studies in the history of climate science) was that of Michael Mann and colleagues published in 1998. That study produced the famous hockey stick graphic showing present-day temperatures to be higher than at any time in the past 600 years. Since then there have been quite a number of analyses that have for the most part confirmed Mann et al’s basic conclusion. Most recent is the work of Marcott et al who concluded that the present global temperatures are warmer than at any time over the past 5,000 years.

Earlier this week a paper appeared online in the journal Nature Geoscience describing yet another temperature reconstruction. But this one has a unique twist. Through an effort called PAGES 2k* involving 78 scientists, individual temperature records for seven "continental scale regions" (Arctic, Europe, Asia, North America, South America, Australasia and Antarctica) were reconstructed for the past 2,000 years. A similar analysis was reported by Osborne and Briffa way back in 2006, but the scale of the PAGES 2k study dwarfs the earlier one.

There are some fascinating insights here about how regions of the globe can at times vary in unison and at other times go off in their own direction. (More at RealClimate and PAGES 2k Network.)

For example, the Antarctic has marched to its own climate drummer at times, remaining warm during the late 16th century when the rest of the globe had already entered a cooling phase. The PAGES 2k team also found that Antarctica is the only region that has avoided the current late 20th century warming.

The study also suggests that the Medieval Warm Period and the Little Ice Age were not global-wide events with all regions acting in unison. In contrast, the authors report, the current warming, as well as the cooling trend that ended in the late nineteenth century, has been, rather atypically, largely global. (A result similar, by the way, to that of Osbourne and Briffa.)

The bottom line for this study is pretty consistent with those reached in previous studies: "during the period AD 1971-2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years."

Gotta run to testify in front of the House Subcommittee on Environment, so that's all for now.


End Note

* The PAGES (short for Past Global Changes) project is an international effort to support all paleoenvironmental and paleoclimate research "directed at securing a quantitative understanding of natural and human-induced variations of the Earth system in the past, in order to make sound predictions of future climate, environment and sustainability." Begun in 1991, the larger PAGES community includes more than 5,000 scientists from over 100 countries. Read more on PAGES here. For details on PAGES 2k, see here and here.

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