An analysis by National Center for Atmospheric Research (NCAR) scientist Jeffrey Kiehl published in the most recent edition of the journal Science in the ‘Perspectives’ section has concluded that the sheer scale of climate change during Earth’s ancient history points to temperatures rising far more than expected in Earth’s immediate future.
Kiehl brought together several studies and combined them with his own mathematical calculations to estimate average global temperatures in the distant past.
“If we don’t start seriously working toward a reduction of carbon emissions, we are putting our planet on a trajectory that the human species has never experienced,” says Kiehl, a climate scientist who specializes in studying global climate in Earth’s geologic past.
“We will have committed human civilization to living in a different world for multiple generations.”
Kiehl looks at the relationship between global temperatures and high levels of carbon dioxide in the atmosphere tens of millions of years ago, and warns that if carbon dioxide levels are not soon moderated by the end of this century, greenhouse gases will reach levels that existed about 30 to 100 million years ago when global temperatures averaged about 16 degrees Celsius (29 degrees Fahrenheit) above pre-industrial levels.
The research showed that if society continues its current increase of burning fossil fuels for energy, the levels of carbon dioxide in the atmosphere are going to reach 900 to 1,000 parts per million by the end of this century, compared to 390 parts per million today, and 280 parts per million in pre-industrial times. This leads to the feared global warming that will create its own feedback loop which itself will continue the growth of the warming.
Drawing on recently published research that showed carbon dioxide levels reaching 900 to 1,000 parts per million 35 million years ago and based on analysing the molecular structure in fossilized organic materials, at the recorded time, worldwide temperatures were substantially warmer than they are today, even in the Polar Regions, and despite the sun being weaker than it is today.
Temperature averages in the tropics were kept at about 5-10 degrees Celsius (9-18 degrees Fahrenheit) above present-day temperatures while in the Polar Regions temperatures were some 15 to 20 degrees Celsius (27 – 36 degrees Fahrenheit) warmer than they are today.
Another aspect to the analysis was looking at Earth’s overall sensitivity to warming, especially on a longer time scale, which none of the current day models are able to accurately predict.
Kiehl, using our past as a modern day computer model, suspects that with the melting of the ice caps, the overall sensitivity towards warming could be twice that which is currently predicted.
“This analysis shows that on longer time scales, our planet may be much more sensitive to greenhouse gases than we thought,” Kiehl says.