Marine climate change

European sea temperatures seem to be increasing. The three primary physical effects of climate change on our seas are increased sea surface temperature, oxygen depletion (hypoxia) and acidification. The combined effects of these phenomena decrease the overall resilience of marine ecosystems and make them even more vulnerable to other pressures. This includes the cumulative impacts of human exploitation.

The life cycles of marine organisms are adapted to a certain temperature range, so they respond to changes in temperature. When temperatures change, organisms either live under sub-optimal conditions, or they move elsewhere. In the sea, these adjustments are happening much faster than on land, but the speed at which they happen differs depending on the species in question.

Annual average sea surface temperature (SST) in Europe’s seas 1871–2015

In recent decades, ocean acidification has been occurring a hundred times faster than during previous natural events over the last 55 million years. Global surface ocean pH has declined from 8.2 to 8.1 over the industrial era (becoming more acidic), and is projected to decline further to 7.8 by 2100 depending on future CO2 emissions. The largest projected decline represents more than a doubling of acidity on today's levels.

When CO2 is absorbed by the ocean it reacts with water producing carbonic acid. It has been shown that corals, mussels, oysters and other marine calcifiers have difficulties constructing their calcareous shell or skeletal material as the concentration of carbonate ions decreases. Most marine calcifying organisms exhibit the same difficulty.

The impact of climate change on marine ecosystems, and particularly those in Europe, is complex, interdependent and not well understood. Ultimately, climate change affects the health and resilience of natural systems, increasing vulnerabilities and social imbalances and causing loss of biodiversity.

The activities causing this pressure are mainly land-based activities, transport, and oil and gas production.

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