Question to the Department for Environment, Food and Rural Affairs:

To ask Her Majesty's Government whether they regard the UK Climate Projections 18 (UKCP18) as an (1) up-to-date, and (2) reliable, tool for the future planning of sea defences; and what assessment they have made of the International Panel on Climate Change's revisions to its high emissions scenario which underpin UKCP18.

Sea level rise projections for the UK were updated in 2018 with the release of latest UK climate projections (UKCP18, Met Office, 2018). The UKCP18 projections for time mean sea level rise around the UK improve on the previous generation of climate projections (UKCP09) through improved understanding of the components of sea level rise (as demonstrated by a better agreement between models and observations) and the inclusion of ice sheet dynamics (Palmer et al., 2018).

The Environment Agency has used the UKCP18 marine projections to derive allowances for sea level rise out to 2125 for each of the six river basin districts in England, based on the 70th and 95th percentiles from Representative Concentration Pathway (RCP) 8.5. These allowances can be found in ' Flood risk assessments: climate change allowances' and are intended to help ensure that new development adequately addresses the future risk of sea level rise. The marine projections are also used to inform sea level rise allowances in Flood and coastal risk projects, schemes and strategies: climate change allowances.

There is a lot of uncertainty around the absolute upper limit of sea level rise this century but the science can provide low likelihood high end scenarios, called H++ scenarios, which can be used in planning. Such a scenario was produced as part of UKCP09. No probability is assigned to these but a range from 0.93 to 1.9 m was considered to be physically plausible and cannot be ruled out (Met Office, 2009). This scenario was designed to encourage people to think about the limits to adaptation from sea level rise. While the marine projections from UKCP18 include ice sheet dynamics, there is still uncertainty around the full range of contributions from ice-sheet melt (in particular from the West Antarctic Ice Sheet), and the assessment of literature available at the time of writing UKCP18 indicated that the H++ scenarios from UKCP09 can still be used alongside the UKCP18 marine projections when considering plausible extreme scenarios.

The Environment Agency currently allows for a full range of future climate (up to and including the 95th percentile of the high emission RCP 8.5 case) in its sea level rise allowances, extended beyond the end of the century, as well as considering the H++ scenarios where appropriate. While these are conservative estimates, using all of the best-available data allows for the uncertainty inherent in climate modelling, the rapid rate of sea level rise we have seen in recent years and the plausible extreme scenarios currently outside of the probabilistic models. The Environment Agency regularly assesses the suitability of climate allowances as and when further information becomes available.

The Environment Agency considers the UKCP18 climate projections to be a reliable and up-to-date dataset to inform future planning for climate impacts, while recognising that uncertainties remain, particularly in future emissions and ice sheet dynamics. The Environment Agency accounts for climate change through the application of allowances when designing and constructing sea defences, using a range of climate change scenarios, including a 4°C rise in global temperatures by 2100. The Environment Agency provides guidance to flood risk management authorities, developers and local planning authorities on how to account for climate change in new flood and coastal risk management schemes and development. In July 2020, the Environment Agency updated this guidance to account for future sea level rise and on 20 July 2021 updated the guidance to account of future increases in peak river flows.

The Met Office will continue to assess the science of sea-level rise as part of the Met Office Hadley Centre Climate Programme, including examining the implications of the next IPCC assessment. It is not possible to comment on the content of the next IPCC assessment ahead of its publication. However, we do note that the model assessment exercise on which the IPCC assessment is based, called the Coupled Model Intercomparison Project Phase 6 (CMIP6), used a range of emission scenarios including one with a similar level of radiative forcing to RCP8.5.