Carbon dioxide and climate

Dr Peter Köhler, physicist at the Alfred Wegener Institute.

Climate sensitivity

Carbon cycle

CO₂

Negative emissions

¹⁴C

The concentration of carbon dioxide (CO₂) in the atmosphere and the global mean surface temperature are in direct interaction with each other. An increase in the CO₂ concentration leads to a warming, a decrease to a cooling of the surface temperature. The extent to which the CO₂ concentration in the atmosphere leads to global warming is being investigated within the concept of climate sensitivity. It indicates how much long-term warming occurs from a given CO₂ concentration. At the same time, warming the oceans means that the oceans can store less CO₂, because the solubility of gases in seawater is temperature-dependent. This effect of temperature on CO₂ is part of the physical carbon pump, which describes how CO₂ is transported from surface waters into the deep ocean. Both interactions are fundamental to our understanding of the Earth system.

In order to make reliable statements about future global warming, it is therefore essential to test our knowledge of climate sensitivity and carbon pumps using models. To this end, we use climate data from the past. For the carbon cycle, CO₂ measurements on ice cores over the past 800,000 years are available – a data set that was also collected by AWI researchers more than 15 years ago.

For my current research, I use models to interpret the data of the past, but also to make initial estimates of possible effects of potential CO₂ extraction processes – so-called "negative emissions" – for the future. It helps me that the isotopes of carbon, ¹³C and ¹⁴C, are built into my model. They can be used to identify changes in the carbon sources and sinks.

My expertise on carbon isotopes has contributed to the development of the latest international ¹⁴C age calibration curve "IntCal20". This curve is used to connect ¹⁴C measurements of carbonaceous samples with age, an essential application in paleoclimatology and archaeology.