Sea-level is rising
For approximately 3000 years, sea-level was stable but recent observations indicated an increase in the average speed of sea-level rise, currently at 3.5 millimeter per year. The heat distribution in the climate system causes thermal expansion of oceans, continental glaciers melts and mass loss of ice caps, all evenly contributing to the phenomenon. If these processes intensify, recent estimates suggest a mean sea-level rise of 60 cm to 1 meter by 2100. Sea-level rise significantly varies from one region to another. Moreover, this process is further accentuated when combined with other non-climate factors such as soil compaction or loss of sediment supply by rivers… The impacts of sea-level rise are uncertain in many regions and the use of evolution models to address climate forcing is an important tool to help decision-making in urban planning.
By Benoît Meyssignac
The Long-Term Consequences of Climate Change on Oceans
Debates on mitigation and adaptation measures to adopt against climate change are based on observations and estimations over a range of less than 250 years. A recent study by Clark and his collaborators, published in Nature Climate Change, covers extremely long term (over 10 000 years) climate consequences. Their scope is linked to CO2 emissions. According to these scenarios, the temperature increase could exceed the 2 °C limit, and a 2 to 4 meters per century sea level rise could be expected in the next millennium. These results confirm the importance of keeping a large quantity of fossil resources untouched.
By Xavier Capet
Ocean Circulation and Climate: an Overview
Ocean circulation plays a central role in regulating climate and supporting marine life by transporting heat, carbon, oxygen, and nutrients throughout the world’s ocean. As human-emitted greenhouse gases continue to accumulate in the atmosphere, the Meridional Overturning Circulation (MOC) plays an increasingly important role in sequestering anthropogenic heat and carbon into the deep ocean, thus modulating the course of climate change. Anthropogenic warming, in turn, can influence global ocean circulation through enhancing ocean stratification by warming and freshening the high latitude upper oceans, rendering it an integral part in understanding and predicting climate over the 21st century. The interactions between the MOC and climate are poorly understood and underscore the need for enhanced observations, improved process understanding, and proper model representation of ocean circulation on several spatial and temporal scales.
By Bertrand Delorme and Yassir Eddebbar
The ocean is losing its breath
The decrease in oxygen content (deoxygenation) of coastal and oceanic waters worldwide has worsened in recent decades. The main causes are climate change (warmer water holds less oxygen and causes increased stratification, which reduces ventilation, i.e. oxygen replenishment of the ocean interior and estuaries), and measurably higher nutrient concentrations (eutrophication) due to intensified human activities affecting coastal areas. Open-ocean deoxygenation, warming and ocean acidification are all driven by increased atmospheric carbon dioxide (CO2); they constitutes multiple stressors for marine ecosystems, the socio-economic consequences of which are only just beginning to be appreciated.
By Kirsten Isensee (IOC-UNESCO), Lisa Levin (Scripps Institution of Oceanography, San Diego), Denise Breitburg (SERC, Edgewater), Marilaure Gregoire (MARE-ULG, Liège), Veronique Garçon (CNRS-LEGOS, Toulouse), Luis Valdés (IOC-UNESCO) with updates by LL on Aug. 9, 2016.
Ocean, Biodiversity and Climate
The marine environment has played a key role in the history of life and today’s ocean continues its primordial function in the evolution of life and climate. The recognized species diversity in the oceans does not exceed 13% of all currently described living species – fewer than 250,000 – but this can be due partly to our lack of knowledge, especially concerning deep zones of the oceans and microorganisms, and partly to the fact that marine ecosystems and the way of life in such a continuous medium disperse more easily species and they are less predisposed to endemism. In contrast, marine biomass can be considerable. Climate disturbance has a direct role in the loss of biological diversity, and this loss contributes in turn to the deregulation itself.
By Gilles Bœuf
Coral Reefs and Climate Change
Coral reefs are found in only a small percentage of global oceans, between 0.08 and 0.16%, but they shelter about one third of the marine species known today. This ecological success is due to a symbiosis between a coral and an intracellular microalga, commonly called zooxanthellae. “Organismic engineers”, they are the source of the largest biological constructions on the planet. Genuine oases of life, they support the direct sustenance of more than 500 million people in the world from fishing, but they engage human interest also for other reasons: protection of coasts against erosion, high value tourist areas… Ecological services from coral reefs are estimated at approximately 30 billion USD per year. Their growth depends on many factors (light, temperature, pH, nutrients, turbidity…). They are therefore extremely sensitive to the current changes in our environment: water temperature variability, ocean acidification, in addition to localized disruptions (pollution, sedimentation, coastal development, overfishing, marine shipping…). An increase of less than 1 degree above a threshold value is sufficient to cause bleaching. It breaks the coral symbiosis with their zooxanthellae throughout the populations, leading to the disappearance of the reef. Similarly, ocean acidification impedes the formation of coral skeleton and many other biological functions such as reproduction. We actually estimate that approximately 20% of the global coral reefs have already disappeared completely; 25% are in high danger; and 25% more will be threatened by 2050 if positive management action is not taken.
By Denis Allemand
Coral Bleaching, an Imminent Threat to Marine Biodiversity
For thirty years, the ocean mean temperature has been incessantly increasing, which reinforces the intensity and length of coral bleaching. From 2014 to 2016, following an unusual increase in ocean water temperature notably reinforced by a rather marked El Niño phenomenon, scientists observed an exceptionally intense and major bleaching event which could extend beyond 2017. Climate models expect a temperature increase of surface waters from 1 to 3°C by the end of the 21st century, which threatens the survival of coral reefs around the world beyond the year 2050. The resilience level remains low and limited; the stress coral reefs endure is emphasized by other anthropogenic factors (acidification, sea-level rise, overexploitation, pollution…). In order to protect this natural heritage, which over 500 million people depend upon around the world, it is necessary for governments to take action, beyond local measures, towards reducing human impacts on climate.
By Leïla Ezzat and Lucile Courtial
A case for the deep Ocean
Encompassing 95% of the planet’s habitable volume, the deep ocean plays a major role in climate regulation, and thus new pressures on it and its components should be a major concern. The deep sea provides many ecosystem services, such as storing heat and anthropogenic carbon emitted in the atmosphere. These services are key to sequestrating CO2 and CH4 on longer time-scales, as well as in supporting nutrient cycling on which the entire foodweb (and so commercial activities such as fisheries) relies. Heat absorption and redistribution impacts human exploited-species ranges. Already absorbing many pollutants and waste, the deep ocean could also become a place for new activities such as mining. Setting up key mitigation and adaptation measures to climate change will require new knowledge, and implementation of a complete legal framework and management tools.
By Lisa A. Levin, Nadine Le Bris, Erik Cordes, Yassir Eddebbar, Rachel M. Jeffreys, Kirk N. Sato, Chih-Lin Wei, and the climate change work group of DOSI Deep-Ocean Stewardship Initiative
Ecosystem services of the deep Ocean
The concept of ecosystem services (ES) includes the ecological functions and the economic value of ecosystems which contribute to human well-being. This approach is already applied for coastal waters management, but it is rarely applied to the deep sea although it represents 97% of the ocean’s volume. The deep-sea ES include provisioning services such as fish catch or industrial agents, regulation services such as carbon storage, and cultural services such as inspiration for the arts. However, the deep sea is facing increasing pressures in the form of direct and indirect human activities. This synergy of impacts is widely unknown and the lack of regulation regarding certain parts of the ocean requires great caution.
By Jennifer T. Le and Kirk N. Sato
Marine Ecosystem Services in Europe
The concept of ecosystem services (ES) refers to the multiple benefits humans gain from maintaining ecosystem health and functions. This notion has theoretical and practical implications because it frames scientific findings into economic terms to raise awareness of the value of functional ecosystems. It follows that environmental management that incorporates the ecosystem service approach is economically efficient and sustainable. The ES approach is particularly useful for coastal and marine ecosystems because they traditionally lack spatial planning and protective regulation. Moreover, the concept of ecosystem services emphasizes the ocean’s function as a climate regulator, and its crucial role for mitigation and adaptation to climate change. Regional implementation of integrated management already exists in the European Union. The next step now is to apply the ES approach to other, threatened regions such as the Mediterranean in order to ensure ecosystem resilience and service provision.
By Clara Grillet, Claire Bertin, Jennifer T. Le and Adrien Comte
Marine Protected Areas Networks and Climat Change: a Political Advocacy
A healthy ocean will allow better ecosystems resilience to climate change, and consequently a reinforcement of ecosystem services crucial to the planet’s viability. In light of growing pressure on the ocean, which has to include the development of new human activities, political issues must combine CO2 emissions reduction with biodiversity conservation issues. Out of 10,000 marine protected areas worldwide, many only exist on paper. Twenty maritime countries cover 80% of the surface of all marine protected areas. Governance and joint management between public stakeholders, professionals and sea users are major obstacles for MPA networks operations. In order to ensure a viable climate for humanity, international and governmental policies should acquire an adaptation and mitigation logic, and include the ocean as a nature-based solution against climate change.
Ocean, environment, climate change and human migration
The ocean’s role in climate regulation is at the heart of climate change economic and social issues, especially those related to environmental migrations. Although the ocean curbs global warming, it is considerably affected by the major disruption that is climate change. Both its regulation role and the ecosystem services it provides are threatened. Sea-level rise and the increasing frequency of destructive climate phenomena, such as cyclones or spring tides, impact human communities and as a result may trigger migration movements. Anticipating these climate phenomena could reduce the vulnerability of natural environments and the communities relying upon them.
By Christine Causse, Daria Mokhnacheva and Guigone Camus
The ocean in national contributions of Mediterranean states
COP21 marked the enshrinement of national contributions in international climate negotiations. The ocean, presented at COP21 as “the forgotten element” of international climate negotiations, has been put back on the negotiation table. As for all subjects, the ocean had to be fervently defended to access the international political agenda. What are intended nationally determined contributions and how do States prepare them? Today, how is the ocean taken into account by Mediterranean States in their national contributions?
By Louise Ras
Which international law for Ocean and Climate?
The United Nations Convention on the Law of the Sea (UNCLOS) and the United Nations Framework Convention on Climate Change (UNFCCC) shape the legal backbone of sea and climate law on the international level. Framework conventions mark the beginning of specific legal systems that are destined to evolve. The UNCLOS takes into account only in an incidental manner certain aspects affecting climate in relation to the ocean. Climate change creates new challenges for the law of the sea, which then must adapt to tackle its impacts and showcase the ocean’s « regulating » role. Regulation of GHG emissions in maritime transport, ice-melt in the Arctic, or even sea-level rise have become the object of international discussions and call for further legal development. To affirm that the ocean has been completely left out of international climate negotiations would be at the very least imprecise. The ocean was mentioned at several occasions during debates and in international texts as one of the aspects of combating climate change. That being said, these references are incomplete and the relative legal provisions suffer from a limited legal scope. The effects of scientific and political mobilization concerning the links between ocean and climate set conditions for a consolidation of the integration of the ocean in climate law. The inclusion of the term « ocean » in the Paris Agreement, the IPCC special report on “Climate change and the oceans and the cryosphere”, or the existence of an ocean session at COP22 – where the implementation of the treaty will be discussed – all foretell a strengthening of the ocean in the climate regime.
By Bleuenn GUILLOUX and Romain SCHUMM