Most people are familiar with how greenhouse gas emissions are linked to climate change. But it is not just the atmosphere that is being altered; increased CO2 production is also having a huge impact on our oceans.
25 % of all CO2 released each year enters the ocean directly. It reacts with seawater to produce carbonic acid, which lowers pH and can trigger changes in sea temperature, oxygen concentration and productivity. Even under the best-case scenario (where CO2 is restricted to 550 ppm), unprecedented changes will occur in the oceans within the next 100 years. Nothing like this has ever happened in the last 20 million years of the Earth’s history.
Virtually all of the planet’s marine areas are projected to be simultaneously impacted by ocean warming, acidification, oxygen depletion and productivity shortfalls by the year 2100. Only small areas of polar waters will see an increase in oxygen concentration and productivity. So marine plants and animals throughout the world will be forced to rapidly adapt to multiple changes in their environment. But will they be able to cope with these new situations?
Already we have seen how shifts in environmental conditions can damage marine organisms and habitats. Recently, relatively minor warming and acidification led to massive bleaching and growth reduction in coral reefs, devastating whole ecosystems. Further harmful events such as this may result in lasting changes in species’ body size and abundance, and even a reorganisation of global biodiversity.
These predicted changes will also impact human societies. Even under the best CO2 mitigation scenario, 1.4 billion people will be affected by ocean biogeochemistry change. Many of these people live in some of the poorest countries in the world and rely on the sea for fishing, tourism and mariculture. These countries are extremely vulnerable to oceanic degradation and are ill-equipped to contend with these challenges.
If CO2 emissions are not immediately reduced, substantial deterioration of the marine environment is likely to occur. And the situation will only be made worse by other stressors such as rising sea-levels, overfishing and pollution. But if we act now, we can begin to identify which species will be most affected by these changes. In doing so, we will take a step in preparing our own society for a world with a very different ocean.
Reference: Mora C, Wei CL, Rollo A, Amaro T, Baco AR, Billett D, Bopp L, Chen Q, Collier M, Danovaro R, Gooday AJ, Grupe BM, Halloran PR, Ingels J, Jones DO, Levin LA, Nakano H, Norling K, Ramirez-Llodra E, Rex M, Ruhl HA, Smith CR, Sweetman AK, Thurber AR, Tjiputra JF, Usseglio P, Watling L, Wu T, & Yasuhara M (2013). Biotic and Human Vulnerability to Projected Changes in Ocean Biogeochemistry over the 21st Century. PLoS Biology, 11 (10) PMID: 24143135
Image: Mora et al., 2013