Project Overview

Problems to be solved:
In order to quantify the potential climate impact of changing atmospheric constituents such as 'greenhouse gases' two simple measures have been used,
namely 'Global Warming Potential' (GWP) and 'Radiative Forcing' (RF). While these measures are convenient 'metrics' allowing estimation of. potential
climate change in terms of e.g. global mean temperatures from an emission into the atmosphere of greenhouse gases, it has recently been found that these
metrics have shortcomings, in particular when considering short lived, chemically active and not well mixed chemical species.

Scientific objectives and approach
The objectives are to assess current metrics of climate change, e.g. Radiative Forcing and Global Warming Potential as used in the Kyoto Protocol, to refine
metrics of climate change, suitable for climate forcing agents arising from inhomogeneously distributed perturbations of the atmosphere, e.g., aerosols, ozone,
contrails and from gases with different levels of thermal infrared optical thickness and different atmospheric adjustment times, e.g., CO2 versus CH4, and to
evaluate the refined metrics with respect to their usefulness for policy makers.

Several cases of localised emission perturbations of ozone precursors will be defined. Using two different chemical transport models, the indirect impact on
ozone and other greenhouse gases (e.g., methane) will be calculated and radiative forcing will be determined.

Idealised and realistic cases of perturbations of climate change agents will be defined. The equilibrium climate responses to these forcings will be compared
using three different general circulation models, and the causes of disagreement will be analysed.

A review of available metrics of climate change will be made. Available metrics (like radiative forcing and global warming potential) will be applied to the
simulations. Finally, on this basis it will be assessed in which cases the current metrics are sufficiently good predictors of climate change. Refined metrics will be
developed and it will be assessed under which circumstances metrics are good predictors of climate change.

The requirements of policy makers for metrics of climate change will be discussed and formulated. Current and refined metrics will be assessed with respect to
their applicability as tools for decision making.

Expected impacts
The project will contribute to a further development of environmentally effective policy measures under e.g. the UNFCCC and to better control and regulation
of anthropogenic impact on the atmosphere and climate.