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Dear Editor (ClimateRealists.Com)

In his opinion piece “Climate claims fail science test”, Professor Michael Asten has misrepresented our recent research by suggesting that it casts doubt on the link between atmospheric carbon dioxide and global warming.

Our study, published in the journal Nature, is a reconstruction of atmospheric CO2 levels 33-35 million years ago when the ice cap first appeared on Antarctica. In the paper we clearly state that the results are in line with expectations from climate model simulations and theory on how the global carbon cycle ought to respond to the growth of an ice cap over very long periods of time.
Michael Asten says that climate after the ice cap grew was similar to the present day, despite higher levels of CO2. He ignores a vast amount of geological data to the contrary and our clear and fully referenced statement that the world at this time was ‘warmer than today, with no evidence for sustained continental ice caps in the northern hemisphere, and possibly West Antarctica, until much later’.

There is a general correspondence between periods of warmth in the past and reconstructed carbon dioxide concentrations, but we caution against any attempt to derive a simple narrative linking CO2 and climate on these large timescales. This is because many other factors come in to play including other greenhouse gases, moving continents, shifting ocean currents, dramatic changes in ocean chemistry, vegetation, ice cover, sea level and variations in the Earth’s orbit around the sun.

Carbon dioxide levels are currently rising year on year at an alarming and geologically unprecedented rate. Nobody to our knowledge is seriously questioning this, or the sound physics that underpins the greenhouse effect. Instead, it seems, some commentators are choosing to focus on simplistic re-interpretation of records like our own that, taken in isolation, can neither prove nor disprove the greenhouse effect.

We would like to take this opportunity to add our voices to the strong and steady message that the world scientific community is delivering to the Copenhagen negotiators – the greenhouse problem is real, imminent and potentially devastating for the planet, its life, and human civilization. Fortunately it is still not too late to avert the catastrophe.

Professor Paul N. Pearson, Cardiff University Dr Gavin L. Foster, National Oceanographic Centre, Southampton Dr Bridget S. Wade, Texas A&M University