Inclusion of a Model of Dynamic Global Vegetation into an Earth System Model
Ecosystems on the Earth's land surface (i.e. terrestrial ecosystems) react to changing weather and climate. They also react to changing concentrations of certain gases in the atmosphere, such as carbon dioxide (CO2), ozone and water vapour. But what is not so widely known is the fact that these terrestrial ecosystems can also, in turn, influence the very development of weather, climate and atmospheric composition. For example, plants reflect and absorb different amounts of solar radiation than bare soil; plants aid the transfer of water from the soil to the atmosphere; and they photosythesise, taking up CO2 from the atmosphere to grow, compete and reproduce. Truly, the atmosphere and terrestrial ecosystems can be considered to belong to one system, the Earth System.
Despite its importance though, climate models or General Circulation Models, GCMs for short, have traditionally ignored or taken highly simplified approaches in dealing with this tight, two-way coupling. This applies to most of the models considered by the United Nations Intergovernmental Panel on Climate Change (IPCC) as they surveyed the state of knowledge within climate science for their Fourth Assessment Report in 2007. But now considerable efforts are being made by many modeling groups around the world to further develop GCMs by improving the representation of the complex processes that link terrestrial ecosystems and the atmosphere.
Researchers within LUCCI WP5 are highly involved in one such effort as partners within the EC-Earth consortium, which is a group of European national weather services (including Sweden's SMHI) and research institutes that together have developed a new GCM (called EC-Earth) for analysis of historical and future climate change scenarios.
Our role within LUCCI is to take the latest version of the LPJ-GUESS model, which is a model of dynamic global vegetation that has been developed and tested largely in Lund over the past decade or so, and to couple it to the other model components within EC-Earth, such as the atmospheric model, and a model of atmospheric chemistry. Once completed, this coupling will, for example, allow the atmosphere in the model to react directly to changing vegetation and ecosystems within LPJ-GUESS, and in turn model the direct and long-term reactions of global ecosystems to various scenarios of climate change. Exchanges of heat, water, momentum, and important biogeochemical compounds such as CO2, methane (CH4), ozone, and volatile organic compounds will be treated consistently, and in a way that has seldom been achieved previously.
The final, fully coupled model will be used by both LUCCI and other EC-Earth researchers to analyse the many feedbacks between terrestrial ecosystems, climate and atmospheric chemistry within the Earth system, in simulations conducted to analyse various scenarios of climate change. Will these feedbacks tend to increase manmade climate change, or dampen it? Or will the most important affects be local in nature? We will begin to answer these questions once the first model runs are carried out in the summer of 2011!