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<p>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).</p><p> </p><p>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.</p><p>
</p><p>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.</p><p> </p><p>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.</p><p> </p><p>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.</p><p> </p><p>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.</p>
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