Research Confirms That Carbon Dioxide Led To Higher Temperatures In The Past

Over the past 400,000 years, the amount of carbon dioxide in the Earths atmosphere has periodically fluctuated, and along with it, so have global temperatures. When the concentration of CO2 has increased, global temperatures have also seen an increase and vice versa.

The basic atmospheric chemistry, which as been well-studied since the 19th century, suggests that the increased concentration of CO2 is driving the increase in temperatures. All else being equal, if you introduce more CO2 into a gaseous mixture containing mostly nitrogen and oxygen, like our atmosphere, youll see more heat trapped something you can demonstrate easily in the laboratory. However, untangling cause and effect in historical events can be tricky, especially in this case, where the evidence is drawn primarily by examining evidence from Antarctic ice cores.

Some earlier studies had suggested that the increased temperatures seen over the past 400,000 years actually preceded the increase of carbon dioxide concentration. While more recent research has cast significant doubt on those findings, a debate among some climate researchers over the causal relationships has remained.

CO2 concentration over the past 400,000 years. (Credit: NASA)

That may change now thanks to a new mathematical analysis from an international team led by Egbert van Nes of Wageningen University. To develop their conclusions, the team utilized a method to detect causality in complex systems developed by George Sugihara. These methods have been successfully used to determine issues of cause and effect in ecological systems where some variables may be dependent on one another, such as the relationship between sardine and anchovy populations with ocean temperatures in the Pacific Northwest. (For details on those original methods, see this paper.)

Use of this statistical method, the authors write, allows us to circumvent the classical challenges of unravelling causation from multivariate time series.We build on this insight to demonstrate directly from ice-core data that, over glacialinterglacial timescales, climate dynamics are largely driven by internal Earth system mechanisms, including a marked positive feedback effect from temperature variability on greenhouse-gas concentrations.

In other words, this new model allows climate researchers to confirm that the known chemistry of greenhouse gasses helped drive positive feedback loops that led to increases in global temperatures. Even in a case over the past 400,000 years where the temperatures may have started to rise first, the subsequent increase in carbon dioxide helped to drive those trends upward when they might have otherwise leveled off or declined.

Our new results confirm the prediction of positive feedback from the climate models, research team member Tim Lenton said in a statement. The big difference is that now we have independent data based evidence.

Average global temperatures by decade. (Credit: World Meteorological Organization)

This new paper is significant as it provides further validation for current climate models and provides yet another resource to demonstrate the consequences of rising carbon dioxide concentrations in the Earths atmosphere. From the perspective of the last 400,000 years, were currently entering uncharted territory. The amount of carbon dioxide in the atmosphere now exceeds any concentration seen during that period of time. And the results are predictable the past few decades have seen increased average temperatures. Last year, 2014, was the hottest year on record since 1880.

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Research Confirms That Carbon Dioxide Led To Higher Temperatures In The Past