Earth hotter today than ever in the past 11,300 years

Earth's temperature is higher than it has been in the last 11,300 years, and is rising faster than ever, scientists have found.

Using data from 73 sites around the world, scientists reconstructed Earth's temperature history back to the end of the last Ice Age, revealing that the planet today is warmer than it has been during 70 to 80% of the time over the last 11,300 years.

Projections of global temperature for the year 2100, using climate models evaluated by the Intergovernmental Panel on Climate Change (IPCC) show that temperatures will exceed the warmest temperatures during that 11,300-year period known as the Holocene under all plausible greenhouse gas emission scenarios.

"We already knew that on a global scale, Earth is warmer today than it was over much of the past 2,000 years," Lead author Shaun Marcott, from Oregon State University's College of Earth, Ocean, and Atmospheric Sciences, said.

"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 civilisation," Marcott said in a statement.

"When you combine the data from sites all around the world, you can average out those regional anomalies and get a clear sense of the Earth's global temperature history," Peter Clark, an OSU paleoclimatologist and co-author on the Science article.

Researchers say over the past 5,000 years, the Earth on average cooled about -17 degree Celsius, until the past 100 years, when it warmed again, according to the study published in the journal Science.

The largest changes were in the northern hemisphere, where there are more land masses and greater human populations.

Climate models project that global temperature will rise another -16.7 to -11.3 degrees Celsius by the end of this century, largely dependent on the magnitude of carbon emissions.

"What is most troubling is that this warming will be significantly greater than at any time during the past 11,300 years," Clark said.

Marcott said that one of the natural factors affecting global temperatures over the past 11,300 years is gradual change in the distribution of solar insolation associated with Earth's position relative to the Sun.

The research team, which also included Jeremy Shakun of Harvard University, primarily used fossils from ocean sediment cores and terrestrial archives to reconstruct the temperature history.