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What is already happening?
  • Sea surface temperature (SST) around the UK generally shows a significant warming trend of around 0.3°C per decade over the last 40 years. 
  • Regional variations exist in this trend with surface warming being greatest across the southern North Sea and least across the north-west of the domain.
  • Warm-season (Autumn) near-bottom temperatures have increased significantly across the southern North Sea over the last 30 years, but not across other regions of the domain.
  • Compared to 1982–1998, the annual number of marine heatwaves increased around the British Isles by an average of four events per year in the period 2000–2016. Larger increases of up to six additional events per year occurred to the north of the British Isles. Smaller changes occurred to the south of the region.

High evidence, high consensus

Sea-surface temperatures are one of the most-measured parameters in the ocean and as a result there is an abundance of evidence. Measures of sea temperature at various depths are also well-established, although the data are generally only available for specific sites or sampling regions/lines. Although some of the observational records are shorter than others and have variable spatial sampling (from point observations obtained from moored buoys through to complete global coverage provided by satellite observations), they all offer a coherent picture of both long-term and shorter-term variability, giving rise to a higher level of confidence in the results. Indices relating to changes in marine heatwaves are a relatively new line of evidence but these are based on well-established datasets of SST

What could happen in the future?
  • Model simulations indicate a continuing warming trend around the UK, with average annual mean SST values of 3.11°C (±0.98°C) predicted for the end of the century (2079–2098) greater than current conditions (2000–2019) under the business-as-usual RCP8.5 scenario.
  • The warming is expected to be greatest across the North Sea in both SST and bottom temperatures, which is a continuation of the spatial pattern of trend observed in recent decades. The warming is expected to be weaker at the surface in the subpolar North Atlantic.

Medium evidence, high consensus

There is high confidence in the global rise in SST and there is high confidence in the long-term future warming trend. However, our confidence in the exact rates of warming at regional scales is lower. An update has been made to the end-of-the century projections used in the previous MCCIP report on temperature, and preliminary results are presented in this report. These simulations provide improvements to the projected temperature change around the UK and to the uncertainty in the predictions. Given the nature of the broad NWS it remains difficult to use global seasonal and decadal predictions for the seas around the UK. Nonetheless, recent research has indicated improved skill in winter predictions for certain regions around the UK using downscaling techniques.

Key Challenges and Emerging Issues
  • Improve our understanding of changes in the near-shore environment (both long term trends and short-lived extreme events) and the connections between the open ocean changes and shelf-sea temperatures (including the causes and effects of change in the North Atlantic subpolar gyre); and how these affect industry, society and ecosystems. 
  • Improve gridded data products of marine air and sea temperatures to be of a higher spatial and temporal resolution and to extend further back in time.
  • Advance modelling of climate change by constructing a more thorough treatment of different sources of climate uncertainty in projections, by producing more accurate predictions (monthly-seasonal; sub-decadal) and near future decadal and multi-decadal projections, and by downscaling these to relevant regional scales.