The research proposed here aims to help us understand year-to-year variations in climate around the world. This includes the occurrence of floods and droughts, of heat waves and cold spells. To do this, we are going to examine the largest source of year-to-year climate variability on Earth, namely, El Niño. The El Niño is a warm ocean current that appears off the coast of NW South America every 3-5 years, and it is a result of a much larger scale phenomenon involving changes to the winds, rainfall, temperature and ocean currents across the whole of the tropical Pacific. The larger scale phenomenon is known as the El Niño Southern Oscillation, a name which reflects the fact that it involves a natural cycle in the circulation of both the atmosphere and the surface ocean and how they interact. Although we know that ENSO originates in the tropical Pacific, it has near world-wide impacts because of the way it affects the circulation of the atmosphere, and hence the winds and transport of moisture from the tropics to the extra-tropics. Floods and droughts and changed incidence of storminess from El Niño directly affect the lives and livelihoods of well over a billion people, and major El Niño events are associated with tens of thousands of human deaths, billions of pounds of damage, and devastation to some natural ecosystems such as coral reefs. Even Europe experiences changed weather patterns associated with ENSO! Although we now understand quite well the basic mechanisms behind the ENSO cycle, some major questions remain. In particular, we do not understand why some El Niño events are much stronger than others, why some decades show much stronger El Niño activity, or how ENSO will respond to climate change. To help answer some of these questions, we will reconstruct changes in ENSO over the past 5,000 years by analysing growth rings in the skeletons of old dead ('fossil') corals that lived in the Galápagos. The Galápagos Islands experience extreme changes in weather associated with El Niño (warmer and wetter during events), and these changes are recorded in the chemistry of the skeletons of corals living in the surrounding ocean. Some of these corals live for up to a hundred years, or longer, laying down layers of skeleton a bit like tree rings. We will collect cores through old dead corals, including some that lived thousands of years ago. Then, by analysing the chemistry of their growth bands we will be able to reconstruct the changes in climate, and ENSO, that the corals experienced during their life time. By combining the records from many such corals we will build up a picture of the natural variability in ENSO, helping us see how often major events occurred, and how much decade-to-decade variability in ENSO occurred. These coral records can let us reconstruct the history of past changes in ENSO, but on their own they do not help us to understand the causes of the changes. Were they due to changes in the sun's radiation? Or due to the cooling effects of major volcanic eruptions? Or were they simply random variations that we should expect without any sort of trigger? To answer these questions, we need to use climate models. The same models that we now use to predict future climate can be used to research changes in ENSO. In our work, we will use the most up-to-date climate models to see if they can correctly replicate the observed changes in ENSO over the past few thousand years as defined by our coral records. We can also see what the effects are of changing volcanic eruptions, solar radiation and greenhouse gases in these models. By comparing the model results with the coral records we will get a better understanding of the nature and causes of changes in ENSO, and the skill of the models at predicting this. In this way we will make a significant contribution to helping predict the likely range of ENSO-related climate events for the coming decades.

There is widespread concern about how climate is responding to the on going rise in atmospheric CO2 from carbon emissions and land use changes. In our view, the climate response can be divided into the following stages: 1. Past and on going increases in atmospheric CO2 are leading to a global warming of up to 0.6C over the last 50 years. The regional variability is though much larger than this global signal. 2. Continuing emissions are increasing atmospheric CO2 and driving a heat flux into the ocean, leading to ocean warming and steric sea level rise. The amount of warming is sensitive to the carbon emission scenario, as well as the rate of carbon uptake by the ocean and terrestrial system. 3. The regional distribution of warming and steric sea level rise is sensitive to how the ocean interior takes up heat, involving the transfer of surface properties into the thermocline and deep ocean. 4. After emissions cease, there will be a thermal adjustment of the lower atmosphere, and the net heat flux into the ocean will cease, and so ocean warming and steric sea level will eventually likewise cease. 5. As well as a thermal equilibrium being reached, the atmosphere and ocean approach a carbon equilibrium after emissions cease, on a timescale of perhaps several hundred years to a thousand years. At this equilibrium, the final atmospheric CO2 and the amount of climate warming is related to cumulative carbon emissions based on our idealised theory. The climate warming and steric sea level rise will be investigated using diagnostics of (i) present day temperature and salinity observations, allowing the steric sea level to be diagnosed; (ii) thought experiments with a range of ocean and climate models on timescales of centuries to several thousand years, designed to explore how the ocean warming spreads from the sea surface into the ocean interior, which ultimately determines the steric sea level rise; (iii) comparison with diagnostics of state of the art climate models, integrated for a century; (iv) comparison with idealised theory, relevant for when emissions cease; and (iv) finally a down scaling to provide bounds on the steric sea level response on a regional scale. This combination of the theory and Earth System models of intermediate complexity will allow a wide parameter space to be explored for a range of emission scenarios, much broader than that usually employed within IPCC assessments for the next 100 years. The study has the potential to provide accessible bounds for steric sea level rise, relevant for policy makers interested in different energy policies, and a link to end users is provided via the collaboration with the Hadley Centre.

Society is becoming increasingly aware of climate change and its consequences for us. Examples of likely impacts are changes in food production, increases in mortality rates due to heat waves, and changes in our marine environment. Despite such emerging knowledge, precise predictions of future climate are (and will remain) unattainable owing to the fundamental chaotic nature of the climate system and to imperfections in our understanding, our climate simulation models and our observations of the climate system. This situation limits our ability to take effective adaptation actions. However, effective adaptation is still possible, particularly if we assess the level of precision associated with predictions, and thus quantify the risk posed by climate change. Coupled with assessments of the limitations on our knowledge, this approach can be a powerful tool for informing decision makers. Clearly, then, the quantification of uncertainty in the prediction of climate and its impacts is a critical issue. Considerable thought has gone into this issue with regard to climate change research, although a consensus on the best methods is yet to emerge. Climate impacts research, on the other hand, has focussed primarily on a different set of problems: what are the mechanisms through which climate change is likely to affect for example, agriculture and health, and what are the non-climatic influences that also need to be accounted for? Thus the research base for climate impacts is sound, but tends to be less thorough in its quantification of uncertainty than the physical climate change research that supports it. As a result, statements regarding the impacts of climate change often take a less sophisticated approach to risk and uncertainty. The logical next stage for climate impacts research is therefore to learn from the methods used for climate change predictions. Since climate and its impacts both exist within a broader earth system, with many interrelated components, this next stage is not a simple transfer of technology. Rather, it means taking an 'end-to-end' integrated look at climate and its impacts, and assessing risk and uncertainty across whole systems. These systems include not only physical and biological mechanisms, but also the decisions taken by users of climate information. The climate impacts chosen in EQUIP have been chosen to cover this spectrum from end to end. As well as aiding impacts research, end-to-end analyses are also the logical next stage for climate change research, since it is through impacts that society experiences climate change. The project focuses primarily on the next few decades, since this is a timescale of relevance for societies adapting to climate change. It is also a timescale at which our projections of greenhouse gas emissions are relatively well constrained, thus uncertainty is smaller than for, say, the end of the century. Work on longer timescales will also be carried out in order to gain a greater understanding of uncertainty. EQUIP research will build on work to date on the mechanisms and processes that lead to climate change and its impacts, since it is this understanding that forms the basis of predictive power. This knowledge is in the form of observations and experiments (e.g. experiments on crops have demonstrated that even brief episodes of high temperatures near the flowering of the crop can seriously reduce yield) and also simulation models. It is through effective use and combination of climate science and impacts science, and the models used by each community, that we will be able to quantify uncertainty, assess risk, and thus equip society to deal with climate change.

The Earth's climate sensitivity / how much it warms as greenhouses gases increase, is arguably the most important 'unknown' in predictions of climate change. Models give a range of approximately 1.5 - 4.5 K for the increase in equilibrium global mean temperature expected when carbon dioxide is doubled. Recently scientists have attempted to use combinations of observations and models to constrain this range / but if anything the range has increased. Uncertainties, mainly in the cloud feedback but also in other feedbacks such as water vapour and ice, account for these large differences between the climate models. These climate feedbacks act to either amplify or reduce the initial effects of the climate change mechanism. Water vapour is the largest positive feedback and acting alone is believed to increase by an amount which roughly doubles the effectiveness of the initial greenhouse gas perturbation. Prime objective: - To evaluate the four main feedback terms in the climate system using observed varaibles. The feedbacks evaluated will be 1) water vapour, 2) clouds (specifically cloud amount, cloud height and cloud optical depth), 3) lapse-rate and 4) surface albedo. A variety of global-scale observations will be combined from many sources and these will be incorporated into offline radiative transfer calculations to gauge the role of these feedbacks in modifying the global energy balance. Uncertainty assessment: - Both the proposed methodology and other more conventional methodologies of calculating climate feedbacks will be assessed in climate model simulations from project partners at the Hadley Centre. These feedback calculations with their model output will be of direct benefit to the Centre who to date have not calculated these feedback terms within their model. These model and data comparisons will be used to: test and assess assumptions used in the proposed methodology, and to quantify realistic uncertainties for each of the feedback terms. - A parallel energy budget calculation by project partners at the NASA Goddard Institute for Space Studies (GISS) will also be used to gauge uncertainty estimates from our analyses. Secondary objectives: - The second aim of the project employs similar methodologies to those of the prime aim to analyse feedbacks on both shorter timescales and on regional scales, and will also analyse feedbacks for different regimes. This work will be used to design diagnostic tests of feedback mechanisms in climate models. Here we will make use of the regime analysis of feedbacks already undertaken by the Hadley Centre. - The third aim of the study is to test the linear model of climate feedbacks: here we will use two different methodologies to evaluate the linear and non linear components of these feeback terms, testing assumptions of non-linearity. Additional output: - We will produce a synthetic dataset of the top-of-atmosphere fluxes, which we will make available to the wider community for their own model evaluation exercises. In summary the project will attempt to quantify some of the largest 'unknowns' in our predictions of global climate change. It will also develop diagnostic tests for feedback analysis in climate models. Overall it will lead to better and more trustworthy climate model predictions, which would not only be of great benefit to the climate modelling community, it would also benefit policy makers who need to rely on the accuracy of such climate model predictions.

Recent satellite observations of the Antarctic ice sheet show dramatic changes over the last decade or so. Two main types of change are seen. The first happens near the coast of the Amundsen Sea and affects several ice streams in the area, such as Pine Island and Thwaites Glaciers. Ice streams are rivers of fast-flowing (up to 1 km/yr) ice that are approximately 40 km wide and several hundred kilometres long, they are separated from the neighbouring slow-flowing (typically 10 m/yr) ice by abrupt shear margins. In these ice streams, the ice appears to be thinning at the rate of several metres per year. The other type of change is found deeper inland on the Siple Coast where one ice stream is thickenning and others show signs of lateral migration. Other evidence (such as buried crevasses) suggest that the flow of the ice streams in this area is very erratic and prone to the occasional shutdown. Air temperatures are so cold in Antarctica that there is very little surface melt and so changes in ice thickness are most likely caused by changes in the horizontal flow of ice, which can lead to thicker ice if the flow slows, or to thinning ice if it accelerates. Researchers believe that the first of the two observations highlighted above may be caused by warming ocean waters around Antarctica. This leads to increased melt from the underside of floating ice shelves, which therefore thin and tend (through buoyancy) to float more. This, in turn, reduces the amount of friction these ice masses experience as they flow over peaks and troughs in the subglacial topography. The net effect is that the ice shelves and their upstream ice streams accelerate and therefore thin. This type of process has been taken as an indicator of contemporary climate change. Until we know the cause of the oceanic warming (if it indeed exists), we will not be able to attribute this thinning to natural or anthropogenic causes. The strange behaviour of the ice streams along the Siple Coast is not thought to happen because of changes in the oceans. This is because the coast in this area is protected by the huge Ross ice shelf and water temperatures in the area are extremely cold. The observations of change in this area could be a reflection of the internal variability of ice flow and the analogy to 'weather' is often drawn. Ice streams are thought to be inherently unstable and prone to surges and periods of stagnation, like their smaller counterparts the valley glaciers. This behaviour may be caused by changes in the flow of water under the ice streams, which affects ice-steam flow because it lubricates any sediments at the base of the ice. Changes in water flow can therefore cause an ice stream to experience more friction and to stagnate. Both of the types of change that have been observed are therefore associated with the dynamics of ice streams. In this project, we want to understand this behaviour by constructing a numerical model of the ice sheet which has sufiiciently fine resolution to capture the the shapes of individual ice streams and ice shelves. This means that we will need to develop a method of doing calculations on a coarse grid for the whole of the ice sheet and on nested, finer grids for individual ice streams and shelves. In order to capture the behaviour described above, we will also have to develop models of new processes such as the transmission of stresses through an ice mass, the flow of water at its base and the interaction between this water and the softness of the underlying sediments. We will also have to integrate satellite observations of the ice sheet to produce an accurate model of its present-day flow. Once complete, the model will be used to assess the longer-term effects of changing ocean temperatures on the ice sheet. It will ultimately provide a tool to help us predict what Antarctica's contribution to future global sea level will be.