PREDICTING THE CLIMATE OF THE COMING DECADE

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The Earth's climate is changing, and there is strong evidence that humans have caused most of the warming in the past 50 years. Until recently, much of the focus of climate science has been on making more detailed predictions of what might happen over the coming century, and especially on providing information to decision makers on likely impacts of a change in climate. This knowledge has motivated changes in policies to reduce greenhouse gas emissions, i.e. mitigation. However, some additional climate change is inevitable, which will require adaptation, regardless of the mitigation policies pursued. Predicting the climate of the next decade is essential because of the urgent need to adapt to a changing climate. For example, a prediction of low future rainfall in Africa would allow advance planning for potential droughts. A judgment on when to replace railway track might include the risks of a heatwave causing lines to buckle, as happened in the UK in August 2003. The diverse range of applications ensures that predicting the climate of the next decade is a fascinating and engaging challenge, with potentially enormous social and economic benefits. To ensure appropriate choices are made, decision makers need to trust the predictions made by climate scientists. But, according to a recent survey, 40% of the British public think the threat of climate change has been exaggerated. To convince a sceptical public and aid decision making, it is essential to build trust in the sophisticated climate models used to make predictions. Every day, similar supercomputer models are used to make weather forecasts which are later compared to what actually happened. This continual assessment allows the models to be improved, building trust in their predictions and ensuring forecasts are more accurate. This fellowship aims to help build the same trust in the models used to predict climate, especially for the coming decade. However, to make accurate climate predictions for the next decade, it is important to realise that the climate changes for two reasons: (i) factors such as greenhouse gases & solar output, and (ii) natural fluctuations. Such fluctuations can temporarily enhance or reduce any long-term trends, especially on regional scales, producing decades where temperatures are warming rapidly and decades when temperatures are stable or even cooling. For example, one third of future decades are predicted to show decreasing temperatures for the UK, i.e. we expect to see periods of cooling temperatures in a warming climate. Without accounting for these fluctuations, the forecasts would be inaccurate, reducing the trust in climate predictions, and so a new strategy is needed. This proposed research will design an improved system for making predictions by analysing the recent past, for example, by only using data available in 1990 to predict the subsequent decade. By improving predictions of the past we can build trust in predictions of the future. To predict these natural fluctuations, we first need to understand their causes. The answers mainly lie in the oceans, which change relatively slowly compared to the atmosphere. The oceans are the main source of natural decadal fluctuations, due to both their large heat capacity and slow changes in ocean circulation. Predicting how the oceans will change over the next decade is essential to predict climate. However, ocean predictions require ocean measurements, which are tricky and expensive to obtain, especially below the surface. It would be more cost effective to target particular locations, rather than the whole ocean. Another vital aspect of this fellowship is identifying sensitive regions of the oceans, and wider 'Earth system' components, such as sea-ice, where small uncertainties cause forecasts to be inaccurate. This research will improve the design of efficient monitoring systems to reduce uncertainty and ensure improved predictions of the climate of the coming decade.