At a global level, current greenhouse gas emissions are most closely following the Intergovernmental Panel on Climate Change's (IPCC) Representative Concentration Pathway (RCP) 8.5 scenario. Within the Bay of Biscay and the Iberian Coast ecoregion, this scenario projects a 1.5°C to 3.0°C warming above mean conditions for the years 2050–2099. Positive anomalies are forecasted everywhere in the region and are most pronounced in the shelf areas (Figure 7).
Climate change has already influenced the Bay of Biscay and the Iberian Coast ecoregion. Studies have shown that sea surface temperatures have increased.
The southern part of the ecoregion (from west of Cape Peñes in the Cantabrian Sea to north of the Gulf of Cadiz) is strongly influenced by upwelling events, which are in turn influenced by wind intensity and direction. Off northern Iberia, upwelling intensifies during northerly winds. The winters of recent years have had more northerlies, coupled with strong upwelling events. Furthermore, it has been demonstrated that winter northerly wind regime shifts have occurred since 2005 in western Iberia.
Upwelling intensity and river outflow off Galicia have been seen to affect the degree of synchrony (and stability) of the zooplankton community, which in turn is likely to impact upper trophic levels.
The timing of the mackerel (Scomber scombrus) fishery has changed, showing an earlier peak of landings in the Cantabrian Sea. This could reflect a change in the timing of migration in response to climate change effects on upwelling patterns.
An increase in the richness of the demersal fish community, together with a western shift in the distribution of many species has been reported in the Cantabrian Sea and Galicia over the last three decades, along with a northwards distributional change of species previously distributed further south. New occurrences and distributional changes of fish in the Bay of Biscay are attributed to increasing temperatures. Examples include changes in the nursery areas of some flatfish and the increased occurrence of deep-water species previously found further south. In contrast, no major distributional trends in demersal fish communities have been observed along the Portuguese continental shelf and upper slope over the last 25 years.
The northwest Iberian Peninsula constitutes the southern limit of the geographic distribution of several canopy-forming seaweeds with cold‑temperate affinities. Since the start of this century, a drastic and general decline of these seaweed species has been observed, with a westward retraction in their distributional ranges. Canopy loss leads to rapid shifts to turf-forming (hydroids, bryozoans) communities, which results in the ecological and functional impoverishment of the coastal system. The decline in these habitat-forming macroalgae has obvious foodweb implications in the intertidal and subtidal areas.
In the Gulf of Cadiz, the African coral Dendrophyllia laboreli, has undergone an expansion in recent years; this has been attributed to increasing temperatures. From the single, isolated, individuals described in 2010, communities now exist in several rocky-bottom sites.
Fish recruitment was reduced by the occurrence of winter northerly winds over the western coast of Portugal at the time of spawning. Sea surface temperature, wind regimes, and river discharges have been identified as factors influencing anchovy early life stages at sea. However, no evidence of the effects of warming have been detected through investigations at one of the essential nursery habitats of anchovy in the Gulf of Cadiz.
A marked decrease in the physical condition of several small pelagic fish, including anchovy and sardine, has been noted in the Bay of Biscay since the mid-2000s. Studies are being conducted to assess the respective roles of density dependence, fishing, and climate change in this weakening of condition.
Sea warming, acidification, and eutrophication have been seen to positively affect the palatability of seagrass in the Gulf of Cadiz, triggering an increase in grazing by sea urchins; this may, in turn, have implications for habitat and trophic regulation changes in coastal areas, with potential consequences for artisanal and recreational fisheries.
Climate‑induced changes in temperature and salinity have affected the biological communities of the Gironde estuary and modified its nursery function for marine juvenile fish and potentially the migration routes of diadromous species.