Washington D.C., USA - The world’s temperature has increased to levels not seen in at least 12,000 years, U.S. climate scientists have reported in the Proceedings of the National Academy of Sciences. Rapid warming has occurred in the past 30 years, the researchers said, and there is little doubt that human activities are the primary factor.

Study coauthor James Hansen of NASA’s Goddard Institute for Space Studies said the new findings imply that the world is “getting close to dangerous levels” of manmade greenhouse gases.

The study concludes the Earth is now reaching and passing through the warmest levels in the current interglacial period, which has lasted nearly 12,000 years. This warming is also forcing a migration of plant and animal species toward the poles, the researchers said.

Worldwide instrumental temperature measurements during the past century show the planet warmed at a rate of 0.2 degree Celsius per decade for the past 30 years. This observed warming is similar to the warming rate predicted in the 1980s in initial global climate model simulations with changing levels of greenhouse gases, the researchers said.

Furthermore, the warming in recent decades has brought global temperature to a level within about one degree Celsius of the maximum temperature of the past million years.

This means that further warming of 1 degree Celsius may represent a critical level, below which the effects of climate change may be relatively manageable, researchers said. During the warmest interglacial periods, the climate was “reasonably similar” to today, they added.

However, if further warming reaches 2 or 3 degrees Celsius, changes are likely to “make Earth a different planet than the one we know” said Hansen, noting that the last time the earth was that warm was about three million years ago, when sea levels were estimated to have been around 25 meters higher than today. Hansen added that global warming is already beginning to have noticeable effects in nature. Plants and animals can survive only within certain climatic zones - the warming of recent decades has thus forced many of them to begin to migrate toward the poles. A 2003 study that appeared in the journal “Nature” found that 1,700 plant, animal and insect species moved toward the poles at an average rate of about 4 miles per decade in the last half of the 20th century.

Hansen said that migration rate is not fast enough to keep up with the current rate of movement of a given temperature zone, which has reached about 25 miles per decade in the period 1975 to 2005.

Another key finding is the temperature change in the area of the Pacific Ocean where the sometimes dramatic weather pattern known as El Niño develops.

An El Niño is a climatic event that typically happens every two to seven years when the warm surface waters in the West Pacific push eastward toward South America, in the process altering weather patterns around the world. Hansen and his colleagues suggest that increased temperature difference between the Western and Eastern Pacific may boost the likelihood of strong El Niños, such as those of 1983 and 1998.

The study comes in the wake of new research documenting increased warming and the effects on the environment, particularly in the Arctic.

European scientists recently reported dramatic openings over large areas of the Arctic’s perennial sea ice pack in August and a study released last week found Greenland’s ice sheet is melting far faster than scientists had previously thought.

Two other studies published this month by NASA scientists confirm that Arctic sea ice is melting at extraordinary rates. One study found that the total amount of Arctic sea ice has fallen by 6 percent over each of the last two winters, compared to a loss of 1.5 percent per decade since 1979.

The second study revealed that perennial sea ice in the Arctic shrank by 14 percent between 2004 and 2005, a striking change compared to the period between 1979 to 2003, when perennial ice decreased at a rate of 9 percent per decade.

See article: The Melting Arctic