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Complex Earth system models, and their various sub-components, are not yet subject to rigorous evaluation against observations as much as they should be, despite the existence of hundreds of proposed diagnostics. A concerted process is urgently needed to make this the norm, not the exception. Earth Observation, field observations and palaeo data can be applied to contexts as diverse as wildfire, marine ecosystems, the land carbon cycle, and greenhouse gases. Model evaluation (by comparing models and benchmark data) and model weighting (defining the ‘quality’ of models on the basis of such a comparison) should be considered as separate issues. Systematic approaches to parameter optimization, such as the adjoint technique, allow structural differences between models to be identified and limitations to be addressed. Such methods are established in atmospheric tracer transport and carbon cycling; research carried out in the QUEST programme has demonstrated their applicability for climate modelling. Although it is impossible to devise a foolproof metric for the ability of models to predict the future, relevant metrics could be based on their ability to simulate the past. Furthermore, it should be possible to extend parameter optimization techniques to assimilate data from the past. There are limits to what can be achieved by benchmarking against a mean state, when it is a change in state that is of greatest interest. It is useful to benchmark individual processes rather than aggregate properties. Coupling good components does not automatically result in a good Earth System model, so for complex models, a two-stage process is needed: first, benchmarking the components in stand-alone mode, and second, using the same benchmarks in coupled mode.

Contemporary increases in atmospheric carbon dioxide concentration are in large part the result of anthropogenic carbon dioxide emissions from fossil fuel combustion. Scenario analysis is commonly used to generate projections of future carbon dioxide emissions, the resulting atmospheric concentrations and climate impact. In most scenario modelling published to date, carbon dioxide emission scenarios are based on demand-side (socioeconomic and technology) factors. The fossil fuel resource is assumed ample enough that supply-side factors do not drive future emission scenarios. This review of the literature on non-renewable resource extraction rate modelling and empirical studies of the global fossil fuel resource base suggests this assumption is unsafe. Supply-side factors can be expected to drive extraction rates and therefore carbon dioxide emissions as fossil fuel resources become significantly depleted. It is likely that the future carbon dioxide emission trajectory will become dominated by supply-side factors during the 21st century. By omitting this possibility, most scenario analysis is too narrow. An implication of such narrow scenario analysis is that policy driven by the UNFCCC‟s agreement to “avoid dangerous climate change” targets only demand-side factors to the exclusion of supply-side factors. As supply-side factors come to drive the carbon dioxide emission trajectory, policy focus should switch from demand-side factors to supply-side factors.

ESS2010 was the first Open Science Conference of the international collaborative initiative AIMES, and was convened and organized by QUEST, the UK's directed research programme for Earth System science. The conference showcased advances in Earth system modelling, deploying observations and process understanding to develop more quantitative and predictive understanding of the interactions of the climate system, the biosphere and the anthroposphere. These tools extend understanding of the system dynamics of biogeochemical cycles, and give perspectives on the relationships between climate, ecosystems and human needs. As Earth system science is a global research endeavour, and its remit has important societal and policy implications, a recurrent theme in the conference was the responsibility of scientists working on knowledge integration in the global environmental change context.

Nitrogen-containing organic matter in rain and aerosol makes up a substantial proportion – 25–35% – of the total nitrogen in atmospheric deposition. Despite this quantitative significance, it is “invisible” in current policy; and existing global air quality and nitrogen deposition monitoring programmes routinely measure nitrate and ammonium but not the organic component. Although recent research, especially in Asia and Latin America, is helping to build up a global picture of organic nitrogen deposition, data sets are sparse and the chemical composition of the organic matter is relatively poorly characterised. As a result, its role in ecosystems and Earth system processes remains unclear. Organic nitrogen should now be included in initiatives dealing with nitrogen deposition and its management.