Impacts of climate change on temperature (air and sea)
Stephen R. Dye, Sarah L. Hughes, Jonathan Tinker, David I. Berry, N. Penny Holliday, Elizabeth C. Kent, Kevin Kennington, Mark Inall, Tim Smyth, Glenn Nolan, Kieran Lyons, Olga Andres and Agnieszka Beszczynska-Möller
Dye, S.R., Hughes, S.L., Tinker, J., Berry, D.I., Holliday, N.P., Kent, E.C., Kennington, K., Inall, M., Smyth, T., Nolan, G., Lyons, K., Andres, O. and Beszczynska-Möller, A. (2013) Impacts of climate change on temperature (air and sea). MCCIP Science Review 2013, 1-12. doi:10.14465/2013.arc01.001-012
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Relative to the underlying warming trend during the 20th century the surface waters averaged over the north Atlantic were cool in the period between 1900 and 1930, warm from 1930 to 1960, cool between the late 1960s and 1990 and then warm to present. The warming observed in the last three decades has been particularly strong in parts of the north-east Atlantic, the sea surface around the UK and Ireland warming at rates up to six times greater than the global average. It remains difficult to fully distinguish the natural variations in temperature from those due to anthropogenic influence (including emissions of carbon dioxide (CO2).
Marine Air Temperatures over the North-east Atlantic and southern North Sea have warmed rapidly over the last 30 years. The observed warming is greatest over seas south of Iceland at faster than 0.6 °C decade-1. Locally the most rapid rises have been observed in the Southern North Sea (Charting Progress Region 2) and off the western coast of Scotland (Region 6 and the southern part of Region 7) at a rate between 0.2 and 0.4˚C decade-1. Recent cold years have meant that linear trends in Marine Air Temperature in other regions (Regions 1, 3 and much of Regions 4 and 5) are not statistically significant. Similarly, sea-surface temperatures (SST) in UK coastal waters and in the North-east Atlantic have risen by between 0.1 and 0.5˚C decade-1 since the 1980s, and fastest locally in Region 2.
The temperature of the upper ocean (0-800 m) to the west and north of the UK has been generally rising since the 1970s (Region 8) and 1980s (Region 7). Superimposed on the underlying upward trend are decadal variations with relative maxima around 1960 and in the 2000s and relative minima in the 1980s and 1990s.
Despite the long-term warming trends, whether over the century or last 30 years, in evidence in most regions, temperature evolution at a location has not been linear or smooth with some short periods of rapid change over a few years and others of little change. Since 2008 the SSTs observed in most areas have not risen or have been slightly lower than observed in 2003-2007. The observed temperature changes have been due to a combination of global climate change and natural variability, attributed to ‘internal’ variability in the ocean atmosphere system, the Atlantic Multidecadal Oscillation is thought to be a representative pattern of this internal variability, the decadal scale patterns observed in UK waters are similar to that of the AMO. As a result of both of these ‘drivers’, a significant period of rapid warming occurred from 1985 to 2003.
West of the UK the water of the deep ocean (>1000m) comes from the Labrador Sea and has generally cooled since 1975. North of the UK, the deep water (800 m) flows from the Nordic Seas and shows no long-term trend since 1950.
Over the 21st century warming in the shelf seas around the UK and Ireland and the upper layers of the North Atlantic is predicted to continue, although perhaps at a lesser average rate to that observed in the last 30 years. Natural variability, driven by atmospheric and oceanic processes introduces a level of uncertainty that makes it difficult to predict the direction of temperature change over the next decade. However, initial experimental forecasts of ocean temperatures are beginning to be published.