The impacts of climate change on the world's oceans include decreased ocean productivity, altered food web dynamics, reduced abundances of habitat-forming species, shifting species distributions, and a greater incidence of disease. Further change will continue to create enormous challenges and costs for societies worldwide, particularly those in developing countries.
Those are the primary conclusions of a review article published in June in Science by John Bruno and his colleague, Professor Ove Hoegh-Guldberg Director of The University of Queensland's Global Change Institute.
The article was a comprehensive synthesis on the effects of climate change on the world's oceans. We concluded that man-made greenhouse gases are driving irreversible and dramatic changes to the way the ocean functions, with potentially dire impacts for hundreds of millions of people across the planet.
Professor Hoegh-Guldberg likes to point out that the ocean, which produces half of the oxygen we breathe and absorbs 30% of human-generated CO2, is equivalent to the planets heart and lungs:
Quite plainly, the Earth cannot do without its ocean. This study, however, shows worrying signs of ill health. We are entering a period in which the very ocean services upon which humanity depends are undergoing massive change and in some cases beginning to fail. Further degradation will continue to create enormous challenges and costs for societies worldwide.
The "fundamental and comprehensive" changes to marine life identified in the report include rapidly warming and acidifying oceans, changes in water circulation and expansion of dead zones within the ocean depths.
These are driving major changes in marine ecosystems: less abundant coral reefs, sea grasses and mangroves (important fish nurseries); fewer, smaller fish; a breakdown in food chains; changes in the distribution of marine life; and more frequent diseases and pests among marine organisms.
Additionally, the distribution and abundance of phytoplankton communities throughout the world, as well as their phenology and productivity, are changing in response to warming, acidifying, and stratifying oceans. The annual primary production of the world's oceans has decreased by at least 6% since the early 1980s, with nearly 70% of this decline occurring at higher latitudes and with large relative decreases occurring within Pacific and Indian ocean gyres. Overall, these changes in the primary production of the oceans have profound implications for the marine biosphere, carbon sinks, and biogeochemistry of Earth.
Among the most clear and profound influences of climate change on the world's oceans are its impacts on habitat-forming species such as corals, sea grass, mangroves, salt marsh grasses, and oysters. Collectively, these organisms form the habitat for thousands of other species. Although some resident species may not have absolute requirements for these habitats, many do, and they disappear if the habitat is removed. For example, mass coral bleaching and mortality, the result of increasing temperatures, is already reducing the richness and density of coral reef fishes and other organisms.
What strikes me the most about the recent science coming out on this topic, is the degree to which we are modifying fundamental physical and biological processes by warming the oceans. The warming doesn't just kill sensitive species, it modifies everything from enzyme kinetics, to plant photosynthesis and animal metabolism, to the developmental rate and dispersal of larval (baby) fish to changing the ways food webs and ecosystems function. And the big surprise, at least to me, is how quickly this is all happening. We are actually witnessing these changes before we predict or model them. This isn't theoretical; this is a huge, real-world problem. Moreover, we, not just our children, will be paying the price if we don't get a handle on this problem very soon.