Challenge 2: Identify and model the processes that govern climate on multi-decadal to centennial time-scales; quantify and reduce the uncertainty in predictions for the next century
The evolution of climate on multi-decadal to centennial time-scales is influenced both by the response of the physical climate system (atmosphere, ocean, land, cryosphere) to anthropogenic forcing and also by a wide range of feedbacks involving interactions between the marine and terrestrial biosphere and changing atmospheric composition. For example, changes in climate cause changes in tropospheric and stratospheric ozone concentrations directly, through the influence of temperature and winds, and indirectly, e.g. by modifying the biogenic emissions of ozone precursors. Equally, ozone is a climate gas and its changes impact the climate system directly, via radiative transfer, and indirectly, e.g. by damaging the terrestrial biosphere and thereby affecting carbon uptake. Such "Earth system feedbacks" have the potential to amplify, or damp, significantly the rate of climate change, and they are a major uncertainty in projections of climate for the twenty-first century. Improved knowledge of these feedbacks is urgently needed to guide the formulation of policies to mitigate climate change, since the impact of any reductions in emissions of greenhouse gases is felt primarily on multi-decadal and longer time-scales.
We urgently need improved quantitative knowledge about feedbacks involving, for example: composition and aerosols; the uptake and transport of heat by the ocean; the uptake and emission of carbon compounds; clouds and water vapour. Developing the appropriate models with the increased complexity to address these issues is a major challenge; exploiting the models of process studies, using new data from satellites, from long-term measurement stations and from focused field campaigns, is a major opportunity.
Advance capability for coupled modelling of the physical climate system and of interactions between climate and atmospheric composition.
Identify the role of atmospheric processes in Earth system feedbacks that have the potential to influence global climate on multi-decadal to centennial time-scales.
Improve model representation of Earth system feedbacks.
Exploit existing and new observations to test Earth system models at a process level and to quantify the relative importance of different feedbacks.
Play a leading role within the NERC community in the development of climate modelling.
Contribute to addressing science questions relevant to climate mitigation policy, including underpinning research required to assess proposed geo-engineering schemes.