Global warming has propelled Earth's climate from one of its coldest decades since the last ice age to one of its hottest -- in just one century.
A heat spike like this has never happened before, at least not in the last 11,300 years, said climatologist Shaun Marcott, who worked on a new study on global temperatures going back that far.
"If any period in time had a sustained temperature change similar to what we have today, we would have certainly seen that in our record," he said. It is a good indicator of just how fast man-made climate change has progressed.
A century is a very short period of time for such a spike.
It's supposed to be cold
The Earth was very cold at the turn of the 20th century. The decade from 1900 to 1909 was colder than 95 percent of the last 11,300 years, the study found.
Fast forward to the turn of the 21st century, and the opposite occurs. Between 2000 and 2009, it was hotter than about 75 percent of the last 11,300 years.
If not for man-made influences, the Earth would be in a very cold phase right now and getting even colder, according the joint study by Oregon State University and Harvard University. Marcott was the lead author of the report on its results.
To boot, the range of temperatures from cold to hot produced since the industrial revolution began are about the same as the 11,000 years before it, said Candace Major from the National Science Foundation, "but this change has happened a lot more quickly."
Far from natural warming
Variations in how the Earth is tilted and its orbit around the sun make for a pattern of planetary warming phases followed by cooling phases across the millennia.
The team's research shows the Earth's overall temperature curve dipping down over about the past 4,000 years, but the downward plod comes to an abrupt halt in modern times.
"If you were to predict -- based on where we are relative to the position of the sun and how we are tilted -- you would predict that we would be still cooling, but we're not," Marcott said.
Instead, the planet is warming up. It hasn't been quite this warm in thousands of years. And it's getting hotter.
By 2100, the Earth will be warmer than ever before, Marcott said. If emissions continue as currently predicted until then, global temperatures will rise "well above anything we've ever seen in the last 11,000 years."
That could be a rise of 2 to 11.5 degrees Fahrenheit, according to the NSF.
What a long-range study means
To get a view on global temperatures that long ago, the researchers studied 73 sediment and polar ice samples, taken from all over the globe. Chemicals found in fossils deep down in the samples span the ages and are good indicators of historic temperatures on Earth, Marcott said.
The scientists did the study to put the global temperature trends into a long-range perspective, Marcott said. Critics of climate change research, which has generally covered the last 1,500 to 2,000 years, have complained that it has been too short-sighted.
They argue that the shorter studies have not taken into account that the warming Earth is seeing today could have happened before naturally -- thousands of years ago.