Atmospheric CO2 has increased by more than 40% over the industrial period, which has driven a series of major environmental changes. Yet, the global ocean is a “climate integrator’’ that absorbed 93% of the earth’s additional heat since the 1970s, keeping the atmosphere cooler but increasing ocean temperature and rising sea level; captured 28% of human-caused CO2 emissions since 1750, but acidifying the ocean; and collected virtually all water from melting ice, furthering sea-level rise.
CO2 reacts with water and turns into carbonic acid. As a consequence of this reaction, the acidity of the ocean rises. “The ocean slows the rise of CO2, but this comes at a price. It gets warmer and turns acid”, says Fortunat Joos climatologist at the Oeschger Centre and one of the authors of the study.
Ocean changes associated with a stringent emissions pathway —i.e., consistent with the Copenhagen Accord’s goal of a global atmospheric temperature increase of less than 2°C by 2100— already carries high risks of impacts for warm-water corals and mid-latitude bivalves. The risk of other impacts will remain moderate if we do not exceed this scenario. Higher emission pathways, such as the business-as-usual path we are currently following, would significantly aggravate the situation: almost all marine organisms the research team considered would face very high risk of impact. Likewise, the risk of impact on ecosystem services such as coastal protection and capture fisheries would become high or very high by 2100. This study also shows that the policy options to address ocean impacts (mitigate, protect, repair, adapt) narrow as the ocean warms and acidifies, i.e. as the world moves away from the +2°C path. As a result, “given the extent of the expected changes, no country is in a safe position, making this issue a worldwide problem that challenges the traditional North/South divide”, says Alexandre Magnan, scientist at IDDRI and coauthor of the paper.
Four key messages are articulated. The ocean strongly influences the climate system and provides important services to humans. Impacts on key marine and coastal organisms, ecosystems, and services from anthropogenic CO2 emissions are already detectable across various latitudes, and several will face high risk of impacts well before 2100, even with stringent CO2 emissions scenarios. Immediate and substantial reduction of CO2 emissions is required more than ever to prevent massive and effectively irreversible impacts on ocean ecosystems and their services. As CO2 increases, the protection, adaptation and repair options for the ocean become fewer and less effective.
Given the contrasting futures outlined in this paper, the ocean provides further compelling arguments for rapid, rigorous and ambitious CO2 emissions reductions. Any new global climate agreement that does not minimize the impacts on the ocean will be incomplete and inadequate.
(Source: Press release CNRS, IDDRI, UPMC)
Gattuso J.-P., Magnan A., Billé R., Cheung W. W. L., Howes E. L., Joos F., Allemand D., Bopp L., Cooley S., Eakin C. M., Hoegh-Guldberg O., Kelly R. P., Pörtner H.-O., Rogers A. D., Baxter J. M., Laffoley D., Osborn D., Rankovic A., Rochette J., Sumaila U. R., Treyer S. & Turley C., “Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios”, Science, Vol. 349 ( 6243) DOI: 10.1126/science.aac4722, 2015
