This week the UN held a Climate Action Summit designed to encourage greater action on the part of world leaders to address the causes and impacts of climate change. The summit was accompanied by a Youth Summit and protest, unprecedented in its size and global coverage. The UN Intergovernmental Panel on Climate Change (IPCC) also issued a special report on the ocean and the cryosphere, which lays out the extreme damage being done to the world’s glaciers, permafrost, and ocean by climate change. IPCC studies serve as the basis for a shared understanding of the changes to earth’s natural systems both now and across a range of greenhouse gas emissions scenarios into the future. This report represents the state of the science regarding impacts on the ocean and cryosphere. It also contains recommendations on needed steps to mitigate and adapt to these impacts. The 100 plus scientists that contributed to the report lay out a stark view of what is to be expected by the end of the century and beyond under multiple scenarios.
The broad conclusion is that we face dramatic change under every emissions scenario with projected outcomes under a business as usual approach being exceptionally grim. However, it is also clear that we have agency; if global emissions are capped in the near term and aggressive approaches are taken to support resilience in marine ecosystems and coastal communities, we may yet avoid the worst impacts.
Q1: What physical changes to the earth’s oceans and cryosphere have already occurred?
A1: The world is experiencing a mass shrinking of the cryosphere that includes significant melting in polar ice sheets, glaciers, and regions of permafrost. For example, the Greenland ice sheet alone is currently losing 278 gigatons of ice per year, and Arctic snow and sea ice cover has decreased by approximately 13 percent every decade since the 1970s.
Driving these trends is the fact that the ocean has absorbed over 90 percent of the excess heat in the atmosphere. This effect has so far buffered us from the most severe impacts, but the buffering capacity is limited, and we have observed a warming trend in the global ocean since 1970. This trend has accelerated over the last 30 years, during which time there has been a doubling of the observed rate of ocean warming and a corresponding doubling in the frequency of ocean heatwaves.
In addition to warming, there has also been a significant increase in the acidity of seawater. This acidification is a result of chemical reactions that occur in saltwater as it absorbs the excess carbon dioxide in the atmosphere. The freshening (from melting ice) and warming of the ocean are causing increased stratification and a slowdown in major current systems. Finally, the melting ice caps and warming temperatures are also combining to drive observable rates of global sea-level rise with an increase of 15 centimeters during the twentieth century. All of these changes are continuing and accelerating with the most extreme rates of change occurring at the poles.
Q2: How are these physical changes affecting marine ecosystems today?
A2: The changes in the physical environment are resulting in several observed shifts in marine ecosystems, including changes to productivity, distribution, geographic range, and the timing of migration patterns across all marine species groups. On average, the report finds that species have been moving poleward at a rate of up to 50 kilometers per decade since the 1950s, but specific examples can be much higher. It is likely that the combination of new species interactions and additional pressures such as overfishing are compounding the physical impacts of climate change and making them worse. The physical effects of warming are resulting in a less productive ocean which in turn means that maximum potential catch of fish stocks and other species is declining. It is estimated that the maximum catch potential declined by as much as 9 percent in some fish stocks during the twentieth century as a result of warming. Because over 90 percent of the world’s fish stocks are either fully exploited or overexploited already, the additional stress from warming is inhibiting the ability of overexploited stocks to recover and increase the likelihood that more species will become overfished.
Tropical coral ecosystems are being severely impacted by current levels of warming and acidification. The report finds that ocean warming is driving an observed increase in bleaching and mortality events and general trend of global reef decline over the last two decades. The combination of warming and acidification is making the recovery of these ecosystems slower and less certain.
In polar ecosystems, the rapid loss of sea ice is opening up new areas of the ocean to sunlight which is paradoxically increasing local productivity at the bottom of the food chain but causing severe problems for predators such as marine mammals and some fish stocks that have adapted to an ice-covered environment. The general trend of poleward migration of species is also especially pronounced in the arctic with whole ecosystems shifting poleward.
Q3: How are these physical and ecosystem changes affecting people today?
A3: For the people and communities that rely on marine resources food sources have become unreliable, economic opportunities uncertain, and traditional ways of life are threatened. For those that live in the coastal zone, sea-level rise is making chronic flooding more frequent and, combined with increases in storm intensity, extreme flooding has become more severe. Erosion has also become a significant challenge in many coastal areas and will require entire communities to move.
Tropical and polar ecosystems have been most affected to date with significant increases in bleaching and mortality events in all the world’s coral reefs and rapid changes in arctic food webs making adaptation difficult. Communities that are currently most at risk are therefore those in low lying areas, arctic or high mountain regions, and small island developing states. For example, natural disasters already cost Pacific Island Countries and Territories an average of between 0.5‒ 6.6 percent of GDP per year with damages from individual storms sometimes far exceeding these numbers. Together, these regions account for 20 percent of the global population or 1.4 billion people.
Q4: What kinds of impacts does the IPCC anticipate across a range of scenarios ?
A4: The report contrasts the significant difference in expected impacts between the current trajectory—or business as usual (designated in the report as “ RCP8.5”)—and the most optimistic scenario in which greenhouse gas emissions are sharply curtailed in the near term (designated in the report as “RCP2.6”). This latter scenario roughly corresponds with the agreed-upon Paris agreement target of capping global temperature increases at 1.5 degrees Celsius. Under both scenarios, significant change is expected to continue throughout this century; but this change is significantly less drastic and begins to level off in many cases by the end of the century if we can dramatically reduce emissions. Under such a scenario, ocean acidity, oxygen content, sea ice extent, and the frequency of ocean heatwaves return to a steady state in the next century. Sea level will continue to rise but more gradually. If we fail to reduce emissions, however, the situation becomes dire. The report only makes projections out to 2300, but every single indicator of ocean health becomes exponentially worse and continues to decline over the next two centuries if we continue business as usual. For example, under a low-emissions scenario, the report predicts sea level rise will rise another foot by 2100 after which sea-level rise begins to level off. Under the high-emissions scenario, this increase jumps to 3 feet by 2100 and to 12 feet by 2300 with a continuing upward trend.
Marine ecosystems face similar diverging fates. Under a high-emissions scenario, global ocean productivity will be severely reduced as a result of significant declines in biodiversity and ecosystem structure and function. The report projects that 89 percent of countries will see an average 10 percent reduction in fisheries catch by 2050 and by 16-25 percent in the twenty-first century. This decrease will be significantly higher in tropical coastal regions. Impacts to coral reefs and other fish habitats are expected to reduce harvests from small scale coastal fisheries by up to 20 percent by 2050, and by up to 50 percent by 2100. Unfortunately, it is precisely these small-scale fisheries that directly support most people with approximately a third of the world’s consumed fish coming from these regions. We must also consider that the global population continues to grow and that the competition for evermore scarce marine resources will increase.
Q5: What are the opportunities to mitigate some of these damages by reducing global greenhouse gas emissions or better prepare society for these impacts?
A5: The report makes clear that we are living in a changed world and that these changes will continue through the coming century. However, the impacts under a reduced-emissions scenario are much less dire than those under a business as usual approach. The first priority is therefore mitigation and reduction of greenhouse gas emissions. However, because of the changes that have already occurred, and those that are already locked in, we must also take steps to adapt and build resilience into our coastal communities and marine ecosystems. The report explicitly calls for a comprehensive, ecosystem-based approach to marine resource management. This means incorporating conservation and precautionary approaches as management strategies and, to the maximum extent possible, reducing pollution and other sources of stress.
To that end, a separate report released by the High Level Ocean Panel For A Sustainable Ocean Economy, identifies opportunities for ocean management as both a source of adaptation and mitigation. The group is composed of 12 heads of state and co-chaired by the prime minister of Norway and the president of the Republic of Palau. They call for increased investments in: 1) ocean-based sources of renewable energy; 2) work toward “net zero” emissions in ocean shipping; 3) significantly expand restoration and protection of coastal and marine habitats to both increase resilience and support storage of atmospheric carbon; 4) expand sustainable approaches to aquaculture and fisheries as part of a dietary shift away from carbon-heavy protein sources; and 5) increase research into carbon storage in the sea bed.
Q6. What should policymakers take away from this report and others like it?
A6. The IPCC report on oceans comes not long after another detailed report on the impacts of climate change on land and agriculture resources and the potential impacts on things like global food supply, migration, and political stability. It also follows the IPCC Special Report on Global Warming of 1.5 °C, which spells out the benefits of holding earth’s temperature rise to no more than 1.5 degrees Celsius above pre-industrial levels—an extremely challenging task. Each of these reports is designed to provide policymakers with a common foundation for understanding the risks and uncertainties posed by a changing climate.
The job of policymakers is to make decisions based on this information to help prepare their communities for the expected changes and take measures to stop the most impacts from occurring by drastically reducing greenhouse gas emissions into the earth’s atmosphere. As these reports make clear, for all the concern over the cost of reducing emissions, the costs of the strongest impacts will be exceptionally severe. They range from the evacuation of small islands nations to a loss of way of life for indigenous communities; from destruction of property values and livelihoods in coastal communities and cities around the globe to the destruction of entire marine ecosystems and a wholesale degradation of the ocean’s natural capital. The report is a timely reminder that as a global community, we are neither prepared for nor doing enough to stop the impact of a changing climate.
For additional insights and discussion, please join the forthcoming “An Ocean of Change: How Climate Change Is Upending Our View of Maritime Sustainability, Sovereignty, and Security" event on October 8.
Whitley Saumweber is director of the Stephenson Ocean Security Project at the Center for Strategic and International Studies (CSIS) in Washington, D.C. Sarah Ladislaw is senior vice president and director and senior fellow of the CSIS Energy and National Security Program.