IUCN: Explaining Ocean Warming


The International Union for Conservation of Nature and Natural Resources (IUCN) released a comprehensive report seeking to explain the Ocean Warming which has been observed and the short and long term impact. The report can be found here and it can also be found at the IUCN web site here

The following is the Executive Summary from the report:

Executive Summary

The scale of ocean warming is truly staggering with the numbers so large that it is difficult for most people to comprehend.

Ocean warming may well turn out to be the greatest hidden challenge of our generation. Whilst some may be aware of the implications of a warming ocean for coral reefs, few know about the many other consequences for the ocean. In 1956 the influential meteorologist Carl- Gustav Rossby, now considered by some as the ‘father’ of ocean warming, speculated that over the course of a few centuries vast amounts of heat might be buried in the oceans or emerge, perhaps greatly affecting the planet’s climate. He warned that “Tampering can be dangerous. Nature can be vengeful. We should have a great deal of respect for the planet on which we live”. His theory has been borne out as the consequences of increasing human activities have indeed injected vast quantities of heat into the ocean, shielding humanity on land, in so doing, from the worst effects of climate change. This regulating function, however, happens at the cost of profound alterations to the ocean’s physics and chemistry that lead especially to ocean warming and acidification, and consequently sea-level rise.

Key warming facts:

  • Sea surface temperature, ocean heat content, sea level rise, melting of glaciers and ice sheets, CO2 emissions and atmospheric concentrations are increasing at an accelerating rate with significant consequences for humanity and the marine species and ecosystems of the ocean.

  • There is likely to be an increase in mean global ocean temperature of 1-4oC by 2100. The greatest ocean warming overall is occurring in the Southern Hemisphere and is contributing to the subsurface melting of Antarctic ice shelves. Since the 1990s the atmosphere in the polar regions has been warming at about twice the average rate of global warming.

  • There is likely to be Arctic warming and ice loss, and possibly the essential removal, in some years, of the summer Arctic sea ice within the next few decades. In the Antarctic the extent of the sea ice has been growing at a rate of ~1.3% per decade, although there is strong inter-annual variability.

  • Over the last 20 years there has been an intensification and distinct change in the El Niño events, with a shift of the mean location of sea surface temperature anomalies towards the central Pacific.

  • Currently 2.5 Gt of frozen methane hydrate are stored in the sea floor at water depths of 200 – 2000 m. Increasing water temperature could release this source of carbon into the ocean and ultimately into the atmosphere.

Marked biological manifestations of the impacts from ocean warming and other stressors in the ocean have taken the form of changes in biogeographical, phenological, biodiversity, community size, and species abundance as well as ecological regime shifts. Such shifts often interfere, or are predicted to interfere, with the benefits we expect from the ocean. More precise interactions, such as the relative importance of direct physiological effects and indirect effects through other abiotic pathways, and species interactions remain largely unknown. The problem is that we know ocean warming is driving change in the ocean – this is well documented - but the consequences of these changes decades down the line are far from clear.

Whilst rising CO2 levels and increasing warming can occasionally have positive effects, the overwhelming evidence and predictions shown in this report are for a cocktail of negative effects, which we are only just starting to understand, but about which we know enough to be very concerned. The warming signs are clear to see, Ocean Warming 11 not only the current prevalence of bleaching of coral reefs around the world, but the increasing confidence of predictions that all coral reefs will be so affected by 2050, unless we change our ways, and quickly. 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.

All these changes and predictions for the future matter from moral, social, ecological and economic perspectives. The value of our relationship with the ocean sometimes seems difficult to cost, but is the ultimate relationship that enables life to exist on Earth. Where it is quantified it runs to trillions of dollars a year, directly and indirectly affecting many of the benefits we have so far taken for granted. The greatest losses will likely fall upon those people who rely upon the ocean for day-to-day subsistence – typically the poorest coastal nations. With issues of such importance at stake we need to vastly improve the science and knowledge available as we move forward into an increasingly compromised ocean world. This is a common conclusion by many scientists who have contributed to this report.

Key recommendations based on the evidence presented in the report are that there is a need for:

Recognition of impact severity. There is a need for a much greater recognition of the unequivocal scientific evidence of impacts on key marine and coastal organisms, ecosystems, and services even under the low emissions scenario (RCP2.6).

Concerted joined-up global policy action for ocean protection. There is a need to join up action across global conventions with respect to climate change and environmental protection.

Comprehensive protection and management. There is a need to ensure that we rapidly fill gaps in protective regimes, such as protecting the High Seas.

Updated risk assessments. A re-evaluation is needed on the risks that impacts from ocean warming and other stressors pose to humanity, to the viability of the very species and ecosystems involved, and to the provisioning of goods and services we derive from the environment.

Closing gaps in fundamental science and capability needs. There is a need to rapidly assess science, observing and modelling capacity and their needs in light of the widespread changes happening from ocean warming and other stressors.

Acting quickly to keep future options open. The concerns among the scientific community that as atmospheric CO2 increases, the options for the ocean (i.e. mitigate, protect, repair, adapt) become fewer and less effective must now be recognized.

Achieving rapid and substantial cuts in greenhouse gases. Greenhouse gas mitigation at the global scale appears to be the overarching solution.

The evidence in this report shows a complex story of change in the ocean, change that is underway, is often already locked in for future decades, and is beginning to impact our lives. This is no longer a single story of challenges to coral reefs, but stories to changes across species and ecosystem scales, and across geographies and the world. It is pervasive change, driven by ocean warming and other stressors that is already operating across scales and in ways we only barely understand. It is critical that we sit up and recognize these issues and act, or we will be poorly prepared if at all for an uncertain changing future.

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