Rising Ocean Temperatures

Breakers
©Michael Viney

While the seas around Ireland have been warming, it is far from straightforward to judge how much is because of climate change. In addition to the North Atlantic Oscillation, an atmospheric cycle that influences winter weather in Ireland and Western Europe, there is the Atlantic Multidecadal Oscillation, in which the seawater surface temperature rises and falls over a cycle of some 50 years. At present the Atlantic is in its warm phase, which is expected to heat up even more over the next 15 to 30 years. But on top of this natural increase come arresting measurements from the Malin Head observatory. 2011-2020 will be the warmest decade on record, with the warmest six years all being since 2015, according to the World Meteorological Organization (World Meteorological Organization, 2020). This undoubtedly has an impact on rising ocean temperatures and aquatic life.

The warming ocean has been affecting some zooplankton already, moving key species northwards by as much as 1,000 km and replacing them with southern species whose larvae – important as fish food – are abundant at a different time of year. Such calendar mismatches of predators and their prey, common to both land and ocean, are one of the more troubling consequences of climate change. But there could be benefits in a higher production of phytoplankton, the single-celled primary plant food of the sea. Species that used to bloom only during spring and summer seem to have a longer season, like many plants on land, and the growth of phytoplankton absorbs huge amounts of CO₂ in the ocean’s exchange of gases with the atmosphere.