WARMING ENDED CENTURIES OF COOLING IN 1800S

Analysis of 2,000 Years of Climate Records Finds Global Cooling Trend Ended in the 19th Century; 20th-century warming, researchers say, "reversed" the trend

April 21, 2013 (National Science Foundation)

“The most comprehensive evaluation of temperature change on Earth’s continents over the past 1,000 to 2,000 years indicates that a long-term cooling trend--caused by factors including fluctuations in the amount and distribution of heat from the sun, and increases in volcanic activity--ended late in the 19th century…[and] the 20th century ranks as the warmest or nearly the warmest century on all of the continents, except Antarctica [Africa excluded due to insufficient data]…

“Global warming that has occurred since the end of the 19th century reversed a persistent long-term global cooling trend…[78 authors from 24 countries who make up the 2K Network of the International Geosphere Biosphere Program (IGBP) Past Global Changes (PAGES) project] note in research published in the May 2013 issue of the journal Nature Geoscience that there were regional differences in temperature evolution…”

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“Because long-range cooling was caused by natural factors that continued to exist in the 20th century, the authors argue, the warming of the 20th century makes it more difficult to discount the effects of the increase of greenhouse gases in the global increase of temperatures measured in recent decades…[The] study was not specifically designed to assess the extent to which temperature changes can be attributed to various natural and human-caused factors…

“The PAGES 2K study aggregates…sources that stand in for actual temperature measurements of past climate…[including] tree-ring analysis, which provides a picture of growth…based in part on air temperatures; tree pollen, which registers changes in dominant species; dome corals, which register sea surface temperatures…; …water molecules contained in ice cores…; and various physical and biological properties of lake sediments…[The] analysis will serve as a benchmark for future studies…”

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