A new study shows further evidence of global warming, according to the Earth Institute at Columbia University.
“Earth's climate warmed more between 1971 and 2000 than during any other three-decade interval in the last 1,400 years, according to new regional temperature reconstructions covering all seven continents,” the press release stated.
The current era of continuing global warming, has allowed a “natural cooling trend” to do a 180. The study, which included the work of over 80 scientists from 24 different nations, was done through research of pollen, tree rings, ice cores, lake and ocean sediments, and historical records from across the globe.
"This paper tells us what we already knew, except in a better, more comprehensive fashion," said co-author of the study and tree-ring scientist Edward Cook. Cook works at the Lamont-Doherty Earth Observatory,
Scientists focused on the Medival Warm Period, stemming from 950 to 1250, as more proof that global warming is manmade.
The study showed that certain areas in Europe and North America were warm while certain areas in North America remained cold.
"If we went into another Medieval Warm Period again that extra warmth would be added on top of warming from greenhouse gases," Cook said.
The study also found that tempetures varied more between continents in the same hemisphere than they did between hemispheres,
According to co-author Heinz Wanner of the University of Bern, the Medival Warm Period is not the only era which shows that humans are at fault for global warming.
"Distinctive periods, such as the Medieval Warm Period or the Little Ice Age stand out, but do not show a globally uniform pattern," Wanner said in the press release.
The study also pointed out the long-term cooling period that occurred within the last 2,000 years. The causes could include changes in land-surface vegetation, slow variations in Earth’s orbit, and the upswing in volcanic activity.
When industrialization began in the 19th century cooling started to disappear. In the 20th century warming was two times a large in the Northern Hemisphere than the Southern Hemisphere. Compared to the late 20th century, some regions saw warmer 30-year intervals during other parts of the last 2000 years. To clarify, years between 21 and 80 AD were most likely warmer than years between 1971 and 2000.
The study was published in the journal Nature Geoscience.
