Addressing the Grand Challenge of regional sea level change prediction

Sea level change is one of the most widely known and potentially serious consequences of climate change due to emissions of greenhouse gases. It concerns both the public and policymakers, because of its adverse impact on the populations and ecosystems of coastal and low-lying areas. This impact is expected to increase for centuries to come.

Sea water expands as it warms in a process known as thermal expansion. Thermal expansion due to changes in the amount of heat entering the ocean is the largest contributor to sea level rise projected for the 21st century. Regional sea level is also affected by changes in precipitation, evaporation and winds over the ocean because, along with heating, these affect ocean density and currents. The contraction of glaciers and ice sheets expected in a warming climate is another important contributor to projected global and regional sea level change, but it is a different scientific subject which we do not propose to address directly here.

Computer climate models disagree in their projections of sea level change. This means that we are not able to make precise predictions of sea level rise on average over the globe. Moreover, while all models predict that some regions will experience a larger rise than average and others a smaller rise than average, they do not agree on these geographical patterns. A large part of the uncertainty is related to the different behaviour of the various models in response to the changing effects of heat, water and winds. They behave differently because different assumptions have been made in their formulations, reflecting a lack of precise knowledge.

This project aims to study these uncertainties, by detailed analysis, using new techniques, of how the ocean models respond to particular inputs, and by comparison with theory and observations. Our aim is thus to reduce the range of the projections. Any such reduction is potentially of large societal and economic benefit; for example, planning decisions need to be made concerning coastal infrastructure that may last for decades and cost billions of pounds.

Sea level change is one of the mostly widely known and potentially serious consequences of anthropogenic climate change, causing concern to both the public and policymakers. In its Fifth Assessment Report, the Intergovermental Panel on Climate Change (IPCC) wrote, "Due to sea level rise projected throughout the 21st century and beyond, coastal systems and low-lying areas will increasingly experience adverse impacts such as submergence, coastal flooding, and coastal erosion. ... Some low-lying developing countries and small island states are expected to face very high impacts that, in some cases, could have associated damage and adaptation costs of several percentage points of GDP."

Adapting to regional sea level change, managing its impacts and increasing resilience depend upon projections. Confidence in our capacity to make projections of sea level change has considerably increased in recent years as a result of improved scientific understanding. However, the quantitative uncertainties in projections of regional sea level remain large, in some regions being of similar size to the best estimate. The proposed project aims to analyse and reduce the uncertainty in projections of sea level change due to ocean density and circulation change. These effects are projected to give the largest global contribution, and have a strong influence on the geographical patterns, dominating in some regions. Hence any reduction of uncertainty is potentially of large societal and economic benefit.

Limiting anthropogenic climate and sea level change requires internationally coordinated action, because it can be done effectively only with global participation. Information about the sea level change to be expected as a consequence of possible future emissions scenarios therefore has an impact on governments worldwide in their negotiations about emissions reduction in the UN Framework Convention on Climate Change. The main channel for communicating policy-relevant scientific results to governments and policy-makers is the IPCC. During the course of this project, the IPCC will prepare both a special report on the oceans and cryosphere in a changing climate and its next comprehensive assessment report on the physical basis of climate change, both on the basis of the published scientific literature, to which we intend to contribute.

Adaptation to sea level change is largely a national responsibility, within an international framework for cooperation. Agencies responsible for coastal infrastructure, such as flood defences, make use of scientific assessments of sea level change when considering necessary measures to protect people, assets and ecosystems from the impacts. Any reduction in uncertainty will be of great benefit to those responsible for decisions concerning infrastructure that in some cases is designed to last for decades and may cost billions of pounds (as in the case of the Thames Barrier, for instance, www.met.reading.ac.uk/research-impacts/case-studies/LondonFlooding.pdf). The PI is a member of the steering committee of the World Climate Research Programme's (WCRP) Grand Challenge on regional sea level change, which aims to support the development of sea level projections that are of increased benefit and utility for coastal zone management.

In the UK, the Met Office provides a channel for communication of science concerning the effects of climate change to government policy-makers and governmental agencies, including the Environment Agency, who are responsible for UK flood defences. The Met Office will be a partner of our project, and the PI is also employed part-time at the Met Office. These links will give us opportunities to ensure that the results of this project have national impact.

The general availability of scientific information is essential to public debate about national and international policy on mitigation and adaptation. Public communication therefore forms part of our plan.