March 8th, 2013 by Joshua S Hill
More data is good data, and more data pertaining to the temperature-history of our planet is definitely good data.
A recent study that took data from 73 sites around the world has allowed scientists to reconstruct Earth’s temperature back to the end of the last ice age, which climaxed 11,300 years ago.
Their findings show that the planet is hotter today than it has been during 70 to 80% of that whole time, a period known as the Holocene epoch.
“We already knew that on a global scale, Earth is warmer today than it was over much of the past 2,000 years,” said lead author Shaun Marcott, a post-doctoral researcher in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences. “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 results of the study were published in the most recent edition of the journal Science, and was funded by the National Science Foundation’s Paleoclimate Program.
Marcott noted that previous research has already shown we are living in one of the hottest periods over the past 2,000 years, but that going back further simply puts today’s climate in a much larger context.
Co-author Peter Clark, a paleoclimatologist from the Oregon State University, said that many previous temperature reconstructions were regional in nature and failed to place their data in a global context.
“When you just look at one part of the world, the temperature history can be affected by regional climate processes like El Niño or monsoon variations,” noted Clark. “But 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.”
The climate history as reconstructed by the Oregon State scientists shows that over the past 5,000 years the Earth has cooled approximately 1.3 degrees Fahrenheit, until the past century in which the temperature has subsequently warmed by 1.3 degrees Fahrenheit. That century fits perfectly with the evolution of our technology and the introduction of fossil fuel industries providing electricity and fuel for vehicles.
This is further played out by the fact the research showed that the changes were most pronounced in the northern hemisphere, which is home to roughly 90% of the human population and more than 65% of the planet’s landmass.
Arguably, more concerning is the predictions that show — under every sensible and plausible greenhouse gas emission scenario — Earth will exceed the warmest temperatures during the past 11,300 year period in the next 90 years. Climate models currently predict that the global temperature will rise another 2.0 to 11.5 degrees Fahrenheit by the end of this century, due primarily to the levels of carbon dioxide that are released and allowed to remain in the atmosphere.
“What is most troubling,” Clark said, “is that this warming will be significantly greater than at any time during the past 11,300 years.”
Troubling to find out is the fact that we should actually be nearing the apex of a long-term cooling trend. Marcott said that one of the natural factors that affects global temperatures is the gradual change in distribution of solar isolation associated with Earth’s position relative to the sun.
“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.”
“The last century stands out as the anomaly in this record of global temperature since the end of the last ice age,” said Candace Major, program director in the National Science Foundation’s Division of Ocean Sciences, which co-funded the research with NSF’s Division of Atmospheric and Geospace Sciences. “This research shows that we’ve experienced almost the same range of temperature change since the beginning of the industrial revolution as over the previous 11,000 years of Earth history – but this change happened a lot more quickly.”
Studies and models outlined in past Intergovernmental Panel on Climate Change (IPCC) reports have attributed our current planetary warming to anthropogenic climate change — human-caused global warming — rather than solar variability or other natural causes.
This long-term reconstruction of our planet’s climatic history helps underscore the assumptions made in the IPCC reports. If climate variability was a major factor in the current warming trend, there is a high likelihood that it would have registered as such in the 11,300 year-long reconstruction. Its absence is testament to the hard work that has gone into climate science over the past 30 years.
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