Earth Warmest in 11,300 Years and Steadily Rising, Scientists Warn

Global temperatures are warmer today than at any time in the past 4,000 years, scientists said Thursday in a new study, and by 2100, they are likely to surpass levels not seen on Earth since before the last ice age.

Scientists from Harvard and Oregon State University conducted a comprehensive analysis of the planet's climate history since the world's ice sheets began their most recent retreat from North America and Europe. The research team looked at ice cores, tree rings and at the fossils of tiny marine organism, in order to chart long-term global warming and cooling trends that date back to the end of the last ice age 11,300 years ago.

"We already knew that on a global scale, Earth is warmer today than it was over much of the past 2,000 years," says Oregon State University post-doctoral researcher Shaun Marcott. "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."

The Holocene period, which began right after the ice age, marked a large increase in global temperatures where ice sheets across the northern hemisphere melted. This is believed to have provided the opportunity for the rise of human kind, about 8,000 years ago.

The research team noted that temperatures in the last decade had not exceeded the Holocene's steamiest periods from thousands of years ago. However, if the world continues to warm at its current rate, those records will be broken by the end of the century.

"By the year 2100, we will be beyond anything human society has ever experienced," said Marcott, in the study.

The Earth, on average, has cooled about 1.3 degrees Fahrenheit over the past 5,000 years. Now in a dramatic turn around, it has begun to warm 1.3 degrees in the past 100 years. The largest changes are visible in the northern hemisphere, where there are more land masses and greater human populations.

The researchers collected data from 73 sites across the globe, on land and beneath the sea. They included ice cores from Greenland, stalagmites in Borneo, and fossilized pollen in Scandinavia. The study was published Thursday in the journal Science.