Mar 8, 2013 12:30 PM ET
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by
AFP
Global warming could have even greater consequences than currently
expected. The Earth is on track to becoming the hottest it has been at
any time in the past 11.3 millennia, a period spanning the history of
human civilization, a study published Thursday has found.
Based on fossil samples and other data collected from 73 sites
around the world, Earth scientists have been able to reconstruct the
history of the planet's temperature from the end of the last Ice Age
around 11,000 years ago to the present.
They have determined that the past 10 years have been hotter than 80 percent of the last 11,300 years.
But virtually all the climate models evaluated by the
Intergovernmental Panel on Climate Change predict that the Earth's
atmosphere will be hotter in the coming decades than at any time since
the end of the Ice Age, no matter what greenhouse gas emission scenario
is used, the study found.
"We already knew that on a global scale, Earth is warmer today
than it was over much of the past 2,000 years," said Shaun Marcott, the
lead author of the study, which was published in Science.
"Now we know that it is warmer than most of the past 11,300
years. This is of particular interest because the Holocene spans the
entire period of human civilization," said Marcott, who is a
post-graduate researcher at Oregon State University.
The data show that temperatures cooled by 0.8 degrees Celsius
over the past 5,000 years, but have been rising again in the past 100
years, particularly in the northern hemisphere where land masses and
population centers are larger.
The climate models project that average global temperatures
will rise by 1.1 to 6.3 degrees Celsius (2.0 and 11.5 degrees
Fahrenheit) by the end of the century, depending on the level of C02
emissions resulting from human activities, the researchers found.
"What is most troubling is that this warming will be
significantly greater than at any time during the past 11,300 years,"
said Peter Clark, a paleoclimatologist at Oregon State.
The Earth's position with respect to the Sun is the main
natural factor affecting temperatures during that time, the scientists
said.
"During the warmest period of the Holocene, the Earth was
positioned such that Northern Hemisphere summers warmed more," Marcott
said.
"As the Earth's orientation changed, Northern Hemisphere
summers became cooler, and we should now be near the bottom of this
long-term cooling trend -- but obviously, we are not."
Other studies have concluded that human activities -- not
natural causes -- have been responsible for the warming experienced over
the past 50 years.
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