Report: Explaining Ocean Warming (the greatest hidden challenge of our generation)

Report: Explaining Ocean Warming (the greatest hidden challenge of our generation)


International Union for Conservation of Nature (IUCN)’ has recently published the report ‘Explaining Ocean Warming (pdf, 460 pages)‘ representing the most comprehensive review to date on ocean warming. IUCN is the world’s largest environmental network, harnessing the knowledge and research of around 1,300 organizations and 16,000 experts. The chapters and sections in the report tells in the scientist’s own words the scale and nature of changes being driven by ocean warming, often in association with other stressors such as ocean acidification and oxygen reductions. The following is an adapted summary of the report’s conclusions and recommendations.

  • Since the 1970s more than 93% of the enhanced heating due to the greenhouse effect and human activities has been absorbed by the ocean, and data show an accelerating upward trend in ocean warming.
  • The ocean has been a vital moderating influence on the global warming up to now having absorbed a significant amount of excess heat and CO2 from the burning of fossil fuels. However, the regulating function happens at the cost of profound alterations of the ocean’s physics and chemistry, especially leading to ocean warming and acidification, and consequently sea-level rise.
  • Even with dramatic cuts of CO2 emissions it will be 50 years before warming will flatten out due to the multi-decadal lag in the climate system. Due to the nature of the deep sea, the effects will continue for decades, if not centuries, even if a complete cessation of CO2 emissions were possible. Looking at the overall consequences of our business-as usual activities, it is clear that we are locking ourselves into an increasingly difficult future for generations to come.
  • Approximately two thirds of the excess heat absorbed by the ocean has been taken up by the upper ocean in the surface to 700 meter depth, with one third absorbed into the deep ocean below 700 meter depth.
  • The CO2-absorptive role of the ocean is predicted to decline the in the 21st century, suggesting that the physics and chemistry of the ocean will be significantly different by 2100. As atmospheric CO2 continues to increase, the solutions (i.e. mitigate, protect, repair, adapt) become fewer and less effective.
  • By absorbing a disproportionate amount of heat from global warming and by taking up the rapidly increasing emissions of CO2, the ocean has so far shielded the world from even more rapid changes in climate.
  • CO2 is the root cause of ocean warming and is also causing ocean acidification. Ocean warming, acidification and oxygen reductions, combined, are driving responses in species and ecosystems, and what is striking is the scale, nature and complexity of these responses and the attendant uncertainties in making detailed predictions.
  • Multiple stressors (warming, acidification and oxygen reductions) interact cumulatively and exposure to one stressor (such as warming) can affect the tolerance of a species to another stressor.
  • Ocean warming and climate change are ultimately contributing to global homogenization of biodiversity, as vulnerable species become extinct and “non-native” species from different biogeographic regions spread, overlap, and become established across the world’s ocean.
  • Ocean warming is causing the expansion of zones experiencing oxygen deficiency, with important consequences for biogeochemical cycling and an increased role for the microbial world, and especially bacteria, archaea and viruses, at the expense of eukaryotes.
  • Oxygen reductions will make the demands of water-breathing organisms, such as fishes and invertebrates, increasingly difficult to meet under global warming scenarios, and will stimulate the production of nitrous oxide which is a potent greenhouse gas approximately 310 times more powerful than CO2. It also has one of the longest atmosphere lifetimes of the greenhouse gases, lasting for up to 150 years. There is evidence that the flux of nitrous oxide from the ocean to the atmosphere is increasing.
  • Greenhouse gas mitigation at the global scale is the overarching solution that will determine the future of all other solutions (protect, repair, adapt).
  • In the light of ocean warming action must be taken to dramatically scale-up area-based, effective, and full protection of marine ecosystems, and to implement much better sustainability measures across the entire ocean.
  • Finally, and most critical, is the need to address atmospheric CO2 and achieve rapid and significant reductions in what we emit. To do otherwise will be to ‘sleepwalk ourselves into a nightmare’, where no level of conservation action in the future will be enough to override the impacts in order to save many of the ocean’s species, ecosystems and benefits we currently rely on and take for granted.


Article in The Guardian about the ocean report: ‘‘.

Abstract on the ocean report: ‘‘.

Article in ClimatePositions: ‘Global ocean temperature january-april 2016 is scary news too (see the graph 1880-2016)‘.


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