Carbon dioxide and climate

Dr Peter Köhler, physicist at the Alfred Wegener Institute.

Climate sensitivity

Carbon cycle


Negative emissions


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.