' are vulnerable to changes that influence the intensity of currents, upwelling and mixing , as well as O2 content, carbonate chemistry, nutrient content and the supply of organic carbon to deep offshore locations .' Climate-change-induced intensification of ocean upwelling in some EBUS, as observed in past decades, may lead to regional cooling, rather than warming, of surface waters and cause enhanced productivity , but also enhanced hypoxia, acidification and associated biomass reduction in fish and invertebrate stocks. Owing to contradictory observations, there is currently uncertainty about the future trends of major upwelling systems and how their drivers will shape ecosystem characteristics . 'Declining O2 and shoaling of the aragonite saturation horizon through ocean acidification increase the risk of upwelling water being low in pH and O2, with impacts on coastal ecosystems and fisheries . These risks and uncertainties are likely to involve significant challenges for fisheries and associated livelihoods along the west coasts of South America, Africa and North America .' 'There is robust evidence and medium agreement that the California Current has experienced  an increase of the overall magnitude of upwelling events from 1967 to 2010 . This is consistent with changes expected under climate change yet remains complicated by the influence of decadal-scale variability .' Declining oxygen concentrations and shoaling of the hypoxic boundary layer likely 'reduced the available habitat for key benthic communities as well as fish and other mobile species. Together with the shoaling of the saturation horizon, these changes have increased the incidence of low O2 and low pH water flowing onto the continental shelf , causing problems for industries such as the shellfish aquaculture industry.' Despite its apparent sensitivity to environmental variability, there is limited evidence of ecological changes in the Benguela Current EBUS due to climate change.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report