Environmental forcing sheds light on carbon levels European research has studied a terrestrial biosphere model to elucidate the mechanisms behind annual variations of carbon in European forest ecosystems. Climate Change and Environment © Thinkstock There are many ways in which the behaviour of an ecosystem can be measured. Healthy ecosystems have a predictable amount of a substance leaving and re-entering, sometimes building up certain substances like carbon as the system develops. Net ecosystem exchange (NEE) is the measurement used to determine how much carbon is entering and leaving the system. Varying values of NEE between years driven by weather and climate are known to contribute to global carbon dioxide (CO2) levels but understanding of the underlying processes is scant. Knowledge on the varying responses of the biotic component (living part) to environmental forcing could help to more accurately predict future levels of CO2 globally. The EU-funded Police project aimed to assess the effects of extreme climate spells as in 2003 compared with those of a 'normal' year on Europe's carbon balance. The summer of 2003 saw the highest temperatures on record throughout the continent. The Police scientists optimised all critical parameters of Orchidee, the new land-surface scheme of the Laboratoire des sciences du climat et de l'environnement (IPSL). They assessed the limits of this process-based model to simulate eddy covariance measurements, an atmospheric measurement technique to calculate vertical turbulent fluxes within atmospheric boundary layers. It is commonly used to determine gas exchange rates of water vapour and CO2 for example. Refining climate prediction models with data on climate changes and their impact can lead to a better understanding of the forces in play and a more accurate forecasting of parameters crucial to the Earth's changing climate.