Earth's Climate: Past, present and future

Science Objectives

Click here for: 
Summaries of the six key themes presented in Cambridge
Introductions to the three lectures on New Insights on Climate Change presented in London
Introduction to the science objectives of the Symposium 
Knowledge of past climate change can be used to improve our understanding of future climate change, but the full benefits of this archive have yet to be realised. This Symposium focused on determining what lessons from the past can be used to inform the future, with the aim of constructing a programme of proposed future collaborative research. If we are to use the past to inform us about the future, we must in some way combine palaeoclimate observations with models of the physical climate system. Such models might be conceptual, mechanistic, or predictive, but in all cases, and for the purposes of this Symposium, they are models that can be applied to the past and to the immediate future out to, perhaps, a few centuries. Our needs with regard to refining our predictions of future climate must be clearly defined, in terms of both model weaknesses and gaps in our understanding of the mechanisms and nature of climate variability. Then we must determine how best to exploit the palaeoclimate record in this context.
Palaeoclimate observations can be used in the conjunction with models in three principal ways. The first is to ensure that models are complete, in the sense that changes and feedbacks observed in the palaeoclimate record are capable of being expressed in the models. The second is to evaluate the fidelity of model simulations of the past using a combination of good palaeoclimate data and appropriate interpretations of that data, together with plausible hypotheses for past climate change whether due to orbital, solar, greenhouse gas or internal variability. The palaeoclimate data needs to be able to distinguish between different models, and those differences need to have some impact on future projections for the test to be relevant. Often the interpretation of the proxy data in terms of a physical climate variable is ambiguous, and so equal attention must be paid to making the model-data comparisons meaningful. A successful model-data match can validate both the model and the hypothesis for past climate change and so aids understanding of the past as well as increasing confidence in projections of the future. The third, more challenging, way is to combine palaeoclimate observations within models of the physical climate system such that model-data comparisons can be tightly coupled.

What type/quality of palaeoclimate observations are necessary? Which palaeoclimate observations are most conducive to the improvement of models or can best distinguish between hypotheses? Which elements of the models are most likely to be tested through use of the palaeoclimate record? Given unlimited resources, which observational campaigns and model developments would most likely yield the greatest insight into future climate in the course of next two decades? Will the palaeoclimate and modelling research trajectories we are currently on be sufficient? Or do we need a change in emphasis, a change in scale, or certain breakthroughs before serious progress is possible? All these questions and others were debated at the Symposium.