WASHINGTON • A new paper is challenging Man's understanding of how long human-caused climate change has been at work on earth.
And the authors say their findings may question existing ideas about how sensitive the planet is to greenhouse gas emissions - with potentially big implications for global climate policy.
The study, published on Wednesday in the journal Nature, suggests that human-caused or anthropogenic climate change has been going on for decades longer than existing temperature records indicate.
Using paleoclimate records from the past 500 years, the researchers show that sustained warming began to occur in both the tropical oceans and Northern Hemisphere land masses as far back as the 1830s - and they are saying industrial-era greenhouse gas emissions were the cause, even then.
"I don't think it changes what we know about how the climate has warmed during the 20th century, but it definitely adds to the story," said Dr Nerilie Abram, an expert in paleoclimatology at the Australian National University and the study's lead author.
People first started keeping organised global temperature records around the 1880s, and these are the records that many scientists make reference to when looking back on how the climate has changed over the last century. And it is clear that it has been warming - and that human activities are the primary cause. But just looking at records from the 1880s onward does not tell the whole story, according to Dr Abram.
"We can see that by only looking from the 1880s on, we don't have the full picture of how we've been changing the climate," she said.
The new research involved 25 scientists from around the world, including more than a dozen researchers from the Past Global Changes 2000 Consortium (Pages 2k) - a group supporting research into the earth's past to gain a better understanding of its climate future.
The Pages team has been involved in creating paleoclimate reconstructions of temperatures over both land and sea. These reconstructions rely on special analyses of coral, tree rings and ice cores, all of which contain chemical fingerprints that can give scientists insights into what the climate was like hundreds or even thousands of years ago.
The research team used these paleoclimate records to look back at the progression of industrial-era warming across the earth over the past few hundred years. The industrial era is a period of time loosely beginning around the mid-18th century, when industrial growth around the world led to a sharp increase in the burning of fossil fuels and the emission of greenhouse gases, which contributed to the onset of anthropogenic climate change on earth.
The team's reconstructions indicated that significant and sustained warming began in the tropical oceans around the 1830s, about the same time it began over the continental land masses in the Northern Hemisphere.