December 2, 2012

Detailing climate change from past to present

With satellites orbiting the Earth, thermometers and other instrumentation galore, scientists have no problem in recording our planet’s weather and assessing our changing climate.

This time scale, however, is measured in decades for the satellites and perhaps 150 years for calibrated instrumentation. But for a full evaluation of Earth’s changing climate, these time intervals are relatively short.

From a variety of sources, such as paintings, manuscripts and journals, historians know there was a warmer period called Medieval Warm Period that lasted from about 950 to 1250. From similar sources there was an intermittent cooler period called the Little Ice Age from about 1300 to 1850.

But just how warm, or cold, was it relative to today?

Enter “proxy data.”

Thus, instead of modern instrumentation, scientists probe lake sediments, tree rings, pollen types, ice cores, mosses, oxygen isotopes, and other information tucked away on or near our planet’s surface to get clues as to how Earth’s temperature has changed. More can be learned about these proxies by searching the Internet.

Let’s look at some recent data that gives us a glimpse of our climate over the past 2,000 years.

The graph of temperature anomaly is from a peer-reviewed paper in Science (Vol. 235, p.1236, 4 Sep 2009) by D. Kaufman et al. The Arctic is probably experiencing climate change faster than anywhere else on the planet. This 2,000-year data are from multiple proxy data distributed across the Arctic, above 60 degrees north latitude.

From this graph we can say: 1) a general cooling trend (straight line) took place over the first 1900 years, 2) a very strong warming trend started about 1900, and temperatures today are far warmer than anytime during the past 2,000 years. A hint of some slight warming (above line) did occur during the early Medieval Warm Period phase, and some uneven cooling did occur at times (below line) during the Little Ice Age.

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