New Evidence of Climate Change: Earth's Current Warming Not Seen in 1400 Years

There's now even more evidence that climate change exists. A new study reveals that Earth's climate has warmed more between 1971 and 2000 than at any other three-decade interval in the past 1,400 years. This period of warming, which continues to this day, actually reversed a natural cooling trend that lasted several hundred years beforehand.

The study involved more than 80 scientists from 24 different nations. Together, they analyzed climate data from tree rings, pollen, cave formations, ice cores, lake and ocean sediments and historical records from around the world. All of the data combined allowed the researchers to better understand the climate history of the planet, and examine exactly what trends have continued into the present day.

In particular, they noted that the Medieval Warm Period, which occurred from 950 to 1250, may not have been global. While parts of Europe and North America were fairly warm during this period, South America stayed fairly cold. This seems to refute the argument that humans are not responsible for modern day global warming and that, instead, the natural warming seen during the medieval ages is actually occurring today.

"If we went into another Medieval Warm Period again, that extra warmth would be added on top of warming from greenhouse gases," said Edward Cook, a co-author of the paper detailing the findings, in a press release. The current warming can, in fact, not be explained by a natural warming trend alone.

While the Medieval Warm Period stood out in terms of warming, it did not show a globally uniform pattern. Instead, the researchers found that temperatures varied less between continents in the same hemisphere than between hemispheres.

By 1500, temperatures dropped below the long-term average everywhere, though colder temperatures emerged several decades earlier in the Arctic, Europe and Asia. In fact, researchers found that the most consistent trend across all regions in the last 2,000 years was a long-term cooling, likely caused by a rise in volcanic activity, a decrease in solar irradiance, changes in land-surface vegetation and slow variations in Earth's orbit.

This cooling, though, began to taper off at the end of the 19^th century--right about the time when industrialization began. The researchers found that warming in the 20^th century was on average twice as large in the northern continents as it was in the Southern Hemisphere.

Yet what is most interesting are the most recent climate events.  The study discovered that Europe's 2003 heat wave and drought, which killed an estimated 70,000 people, actually occurred during the region's hottest summer of the last 2,000 years.

"Summer temperatures were intense that year and accompanied by a lack of rain and very dry soil conditions over much of Europe," said Jason Smerdon, a study co-author, in a press release. The researchers estimate that global warming was just one of several of factors that contributed to the high temperatures.

The study has allowed scientists to get a better view of exactly what has influenced our climate over the past several thousand years. It could also give them the opportunity to better study natural cooling and warming trends.

The findings are published in the journal Nature Geoscience.