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11.300 anni di global warming 11.03.13

Grafico sulle temperature degli ultimi 11.300 anni

Science ha pubblicato un grafico che analizza le temperature medie del pianeta nell'arco degli ultimi 11.300 anni. In poco più di un secolo siamo passati da uno dei decenni più freddi della storia, quello tra il 1900 e il 1910, all'attuale periodo che presenta valori di caldo estremo tra i più alti mai registrati.

The decade of 1900 to 1910 was one of the coolest in the past 11,300 years - cooler than 95 percent of the other years, the marine fossil data suggest. Yet 100 years later, the decade of 2000 to 2010 was one of the warmest, said study lead author Shaun Marcott of Oregon State University. Global thermometer records only go back to 1880, and those show the last decade was the hottest for this more recent time period.

"In 100 years, we've gone from the cold end of the spectrum to the warm end of the spectrum," Marcott said. "We've never seen something this rapid. Even in the ice age the global temperature never changed this quickly."

Using fossils from all over the world, Marcott presents the longest continuous record of Earth's average temperature. One of his co-authors last year used the same method to look even farther back. This study fills in the crucial post-ice age time during early human civilization.

Marcott's data indicates that it took 4,000 years for the world to warm about 1.25 degrees from the end of the ice age to about 7,000 years ago. The same fossil-based data suggest a similar level of warming occurring in just one generation: from the 1920s to the 1940s. Actual thermometer records don't show the rise from the 1920s to the 1940s was quite that big and Marcott said for such recent time periods it is better to use actual thermometer readings than his proxies.