Throughout the world, abundant paleoclimatic evidence suggests that the earth has warmed over the past century to levels not reached for thousands of years. This evidence includes ground temperature profiles, permafrost thawing, range shifts of animals and plants, and changes in the spring flowering dates of plants. Trees found near the margin of the tundra are particularly sensitive to temperature changes. Tree-ring chronologies from these cold region trees indicate a robust growth surge, spurred by climate warming that is unprecedented over the past millennium.

	Modern day glacier and ice coverage of the northern hemisphere ( right), and the same region 18,000 ago.

It is easy to claim, as many skeptics of global warming often do, that computer models of the global climate and paleoclimatic indicators are incomplete and involve uncertainties. This is true and will always be true, of course. We will never know the infinitely complex climate system of earth without uncertainty. And we will never have the equivalent of an evenly distributed network of thermometer and rain gauges covering the globe for the past millennia. But the overwhelming majority of the paleoclimatic records we do have show unprecedented warming of the world since the dawn of the industrial period during the 19th century. This is the simple message of the Ice Man, discovered at 10,500 feet in the Italian Alps after his glacial ice tomb recently melted to reveal his body preserved for over 5000 years.

	The majestic baldcypress has witnessed a thousand years of history, but its numbers are dwindling.

Ironically, anthropogenic climate and environmental change imperil the very records used to reconstruct past climate. The Ice Man's tomb and many glaciers have melted, coral reefs are bleaching and dying from high sea surface temperatures, and ancient forests continue to fall. The large old-growth baldcypress trees at Blackwater River, Virginia, that recorded the catastrophic drought at Jamestown are a remnant of a once widespread clan of millennium-old trees. Centuries of overexploitation have made these trees exceedingly rare. As we celebrate the 400th anniversary of Jamestown Colony and the first English in the New World, we might also remember those ancient trees at Blackwater River that witnessed that history and now stand nearly alone.

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Photos: Mark McCaffrey, NGDC/NOAA; University of Arkansas