The Hot Zone

Reading the leaves

Posted by Alison Hawkes on May 13, 2010
Category : Climates of the Past

We know there’s a relationship between rising levels of CO2 and warmer temperatures. That, of course, is the crux of global warming science and plays an important part in the models that predict future climate change. But looking at the past can be just as informative.

A group of Penn State-led geoscientists and ecologists are shedding light on the matter by looking at the ecological conditions that lead to types of carbon in plants leaves. In a paper published in March 2010 in Proceedings of the National Academy of Science, the team reported a study involving 3,000 modern plants from diverse environments. They looked at two naturally-occurring carbon isotopes — carbon 12 and carbon 13 — in plant leaves to get a better sense of the environmental conditions in which they were growing.

It turns out not just atmospheric carbon impacts these isotope levels, but also water availability and the plant type — deciduous or evergreen. Why does this matter? Sounds a bit roundabout, but the more we know about how plants accumulate different kinds of carbon, the better we can study fossilized plant remains and infer past environmental/climate conditions …. the more we can then understand the future climate.

Fossil Plant, courtesy of the National Park Service

Fossil Plant, courtesy of the National Park Service

“What we hope is that by using this approach, we are going to get a better value for the carbon isotope ratio in the atmosphere, which you then plug into your model and get a better estimate for climate sensitivity,” said Kevin  Mueller, a Penn State researcher.

The group writes about the limitations of studying the recent past:

Human perturbation of the global carbon cycle is potentially far greater in rate and magnitude than variations in the recent past, pushing predictions of future climate beyond the calibration range of models based on modern and near-modern observations.

A longer term, “geologic” view of CO2 levels and ecological patterns is what’s needed.

– Alison Hawkes


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