Chapter 6: Climate Change

Climate change is already having significant impacts on the marine environment and the goods and services it provides. Against the backdrop of natural variation we have evidence that human activities are contributing to a long-term warming trend. Our scientific confidence in projections of future climate varies widely, due to lack of understanding of key processes such as storms and ice melt, and also because we do not know how greenhouse gas (GHG) emissions will change over time. However, climate change caused by human activity is likely to play an increasingly significant role in the changing state of our seas.

Key findings

The world is getting warmer. Global average air and sea temperatures have risen markedly since the mid-20th century and human activities are very probably responsible for much of this.
In the mid- to late 1980s rising sea temperatures were at least partly responsible for a sudden shift in plankton species in UK waters which affected the marine ecosystem.
Distributions of some exploited and non-exploited North Sea fish species have responded to increases in sea temperature by moving northward and to deeper waters over the past three decades.
Warmer sea temperatures since the 1980s have increased the length of the marine growing season.
In some areas of the North-East Atlantic, there are more reports of harmful algal blooms, especially since the mid-1980s.
Recent studies in the offshore North Sea show that low oxygen events in these areas are more likely to be due to climate change than to nutrient enrichment from human sources.
Concerns over climate change impacts on the coast have already increased activity and spending on coastal defences, which will need to double again by 2080.

Main projections

In 2007, the Intergovernmental Panel on Climate Change (IPCC) projected that global mean sea level will rise by 18 to 59 cm during the 21st century, principally through thermal expansion of seawater and melting of land-based glaciers and ice sheets.
Rising sea levels and possible changes to wave conditions will increase ‘coastal squeeze’, habitat loss, coastal erosion and the steepening of intertidal profiles.
Under a medium emissions scenario the latest UK climate information package (UKCP09) projects that UK shelf seas will be 1.5 to 4 °C warmer by the end of the 21st century. UK seas will seasonally stratify in the same locations as now, but this may be stronger, start earlier and break down later each year.
Climate models project that the AMOC will decrease over the 21st century, but not shut down completely. This will not prevent an overall net warming of UK seas.
Unless we reduce human GHG emissions, by the end of the 21st century the acid content of the ocean’s surface water may have doubled. This could adversely affect hard-shelled marine organisms such as corals and molluscs. It could also reduce the ocean’s capacity to soak up CO₂, thus rendering the problem of climate change more severe.

Improvements in assessment methodology and future requirements

We have made considerable progress in assessing the evidence and predicting the consequences of climate change following the establishment of the Marine Climate Change Impacts Partnership (MCCIP). MCCIP was formed following a recommendation from Charting Progress specifically to facilitate the transfer of scientific evidence to decision-makers.

We are beginning to have access to projections of changes in many aspects of the physical environment, for example sea temperature, sea level and acidity. However, these all depend on particular scenario projections for the levels of human-induced GHG emissions.

The evidence for climate change impacts in marine ecosystems is now regularly assessed and updated but an understanding that goes beyond hypotheses of future change in the observed ecosystem impact is limited; and the full impacts of climate change acting through the ecosystem as a whole are a very long way from being understood.

The potential for increasing levels of atmospheric CO₂ to cause changes in the chemistry and pH of the upper ocean is receiving significant attention.

Gaps in knowledge

We now have regular assessments of the evidence for the effects of climate change on marine ecosystems. However we are a long way from understanding the full impacts and predictions of future changes are still largely hypothetical.

Climate change may alter the natural uptake of carbon by the oceans on a scale and in a direction that is presently difficult to predict.

We know very little about the rates of processes leading to ice sheet melting, and hence the contribution of ice sheets to sea level rise – both globally and in UK seas.

For fish and the food webs that rely on them it is difficult to tease out the impacts of climate change from the pressures of fishing activities.

Models are not good at predicting the preferred tracks, strength or frequency of storms into the future.

Carbon dioxide emissions will have a significant effect on the pH and marine life of the UK seas. We cannot accurately predict future CO₂ emissions, and therefore our projections of their likely impacts on the marine life and pH of our seas remain correspondingly uncertain.

Beyond the 21st century, there is currently little confidence in predictions of whether the Atlantic Meridional Overturning Circulation might eventually shut down or what effect changes in this circulation would have on UK climate.

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