Triple threat to the Ocean

© Yanis Zenter

The ocean is the largest ecosystem on Earth. It covers 70% of the planet and has absorbed about 90% the of atmosphere’s heat generated by GHG emissions and taken 30% of carbon emissions, which has dampened global warming. However, this ability to buffer the impacts of climate change has become overloaded:

1. Today the ocean is warmer than at any time since humans began recording climate data in the 1880s. In January 2018, scientists reported that the ocean is warming 40% faster than predicted five years earlier. 

2. The ocean has less oxygen, indeed, warmer water contains less oxygen than cooler water. Direct measurements show that the amount of oxygen in the global ocean has decreased by about 2% in the last 50 years.

3. The ocean is more acidic because the increasing absorption of carbon dioxide from the atmosphere changes the ocean’s chemistry and lowers its pH.

© Generalitat de Catalunya 

Warmer water, decreased oxygen levels and water acidification have huge impactes on the Earth Ocean:

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Thickness of the Artic sea has decreased significantly since the 1960s. Sea ice is projected to decline throughout the 21st century in both hemispheres, and the Arctic Ocean may be ice-free in Summer by 2030.


© Agencia EFE


The global temperature influences water and ice volumes and, hence sea level, which in turn affects coastal habitats and ecosystems. Sea levels have risen during the 20th century and are expected to rise between 0.5 and 1.4 m by 2100. Rising sea levels could mean the end of some island nations and impacts on coastal populations.


© Agents rurals 


Hurricanes and other tropical storms get their energy from warm ocean water. As the upper layer of the ocean warms, hurricanes and other tropical storms become stronger, with faster winds and heavier rain.


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The increased acidity of sea water makes it harder for corals to form their skeletons and for shellfish to build the shells they need for protection. Beyond 2050, corals will become increasingly rare due to ocean acidification.


Who is affected by climate change?

Climate change in the ocean is a reality that already has a significant impact on humans and ecosystems, and the whole living world.

Flora and fauna

On us, humans

The Paris Agreement is a legally binding international treaty on climate change adopted by 196 countries which became effective in 2016. Its objective is to limit global warming below 2°C, preferably not exceeding 1.5°C compared to the pre-industrial era (1850-1900). To achieve this goal, it is urgent that countries reduce GHG emissions to achieve a climate neutral planet by the middle of this century. For the first time, a binding agreement brings together every country in a common cause with ambitious goals to combat climate change and adapt to its impacts.

The ocean as part of the solution to climate change

The ocean is an integral part of the Earth’s climate system and contributes to mitigate and to adapt to climate change. It must be managed according to an ecosystem-based approach, without compromising the ability of future generations to meet their needs. This is in line with the United Nations’ Sustainable Development Goals and is also one of the goals of the Decade of Ocean Science for Sustainable Development (2021-2030). A healthy ocean has the potential to reduce GHG emissions, which is absolutely necessary if we want to reach the Paris Climate Agreement by 2050.

© Jordi Riera

Building resilience with marine protected areas (MPAs)

MPAs can restore ocean health by preserving habitat integrity: they improve ecosystem resilience, support fisheries productivity, protect biodiversity and safeguard unique cultural traditions historically linked to the sea. In addition, MPAs are pilot sites for monitoring climate change and they serve as a link with the scientific community to anticipate steps for more effective adaptation to global warming.

Currently, MPAs with full or high protection cover only 2.6% of the global ocean. Protecting at least 30% of the ocean through MPAs would be ideal to meet a wide range of economic and environmental goals. Despite their key potential role in mitigating and adapting to climate change, most existing MPAs do not have sufficient human or financial resources to adequately implement conservation and management measures. It is essential to increase political commitment to boost the governance of MPAs and their access to resources to deal with climate change.

Climate change impact on flora and fauna


Raising temperature have already determined changes in the distribution of many species around the world. Most frequent distribution shifts occur along the vertical (depth) and latitudinal gradients.


Many organisms around the world are losing suitable habitats due to rising sea levels, more extreme climate and warming, while others are increasingly affected by disease and parasites. By 2070, a third of the planet’s animal and plant species would be in danger of extinction due to climate change, at least at local level.


Normally, Posidonia oceanica blooms in autumn, while its fruits reach full development in spring. However, recent experiments have shown that a simulated heat wave induces flowering in the plant. Heat waves are becoming more frequent in the Mediterranean and their impact on the reproductive biology of marine organisms is still not fully understood.


Higher temperatures are favoring spreading of tropical invasive species at higher latitudes, which has negative effects on resident species and native biodiversity.

Climate change impact on us, humans

Oceans and coastal habitats are a real treasure. Every day they deliver a variety of important ecosystem services, such as moderating extreme weather events, health, tourism, seafood and fish production, and other benefits related to aesthetics, leisure, culture and spirit:


Ecosystems are the first line of defense for coastal communities: they reduce the impact of storms, coastal erosion and flooding. HEalthy mangrove forests, salt marshes, seagrass meadows, dune ecosystems, wetlands and coastal wetlands are better than man-made defence infrastructures !


Depending on the performance of GHG emissions, the maximum catch potential could decrease between 2.8%–12.1% by 2050. The impact will be much greater in some specific regions and the population with the highest levels of poverty – especially small-scale fishers and fish farmers in developing countries – are the most vulnerable to climate change.


At 1.5°C of global warming above pre-industrial levels, the Intergovernmental Panel on Climate Change (IPCC) predicts a loss of 70% to 90% of the world’s coral reefs. At 2°C, this figure rises to 99%. Loss of coral reefs will have a negative impact on the biodiversity and productivity of the oceans and also on tourism.


The ocean allows scuba diving, snorkelling, boat trips, fishing, kayaking, relaxation and other recreational activities that attract tourists from all over the world to coastal areas. Climate change poses a potentially catastrophic threat to all of these activities. To give just one example of its size, the Great Barrier Reef supports a tourism industry worth $6 billion, and 64,000 jobs that depend on a healthy coral reef. Travel and tourism, including indirect and induced impacts, generate on average around 15% of the GDP of Mediterranean countries. An increase in the number of days of extreme heat can seriously affect this sector.