The ocean is the Earth’s vast, life-sustaining circulatory system, covering over two-thirds of its surface. It is a critical engine of the climate, regulating global temperatures by absorbing most of the planet’s excess heat and over a quarter of human-generated carbon dioxide. It is also the Earth’s life support, generating over half of the oxygen we breathe.
The ocean teams with a spectacular variety of life, from photoplanktons, the microscropic organisms that form the base of the marine food web, to blue whales, the largest animals on Earth. This rich biodiversity supports human well-being, providing a crucial source of protein for over three billion people and supporting millions of jobs in fisheries and tourism.
Yet, this immense body of water is now under threat because of anthropogenic climate change. A recent report warns that the planet has reached its first catastrophic climate tipping point, with warm-water coral reefs facing “widespread dieback”. The impending collapse of these reefs heralds a new reality where underwater environments are increasingly unstable, harming both marine ecosystems and humanity. Here are some of the major consequences of the impacts of climate change on the ocean:
Global coral bleaching
Marine heatwaves, one of the causes of coral bleaching, have doubled in frequency, duration, and intensity. Nearly 60% of the world’s ocean surface experienced at least one period of marine heatwaves in 2021. The majority of marine heatwaves arose between 2006 and 2015, leading to widespread coral bleaching and reef degradation. Coral bleaching occurs when coral reefs, under stress, expel symbiotic algae. Although bleaching doesn’t cause direct death, it leaves these invertebrates more vulnerable to starvation and disease, affecting at least 25% of all marine species that rely on coral ecosystems.
A global bleaching event induced by high temperatures has been underway since 2023. Recognised as the worst global bleaching event on record, it has hurt 80% of the world’s reefs across the Pacific, Indian, and Atlantic oceans. According to the UN Environment Programme, if marine heatwaves persist, every one of the world’s coral reefs could bleach by the end of the century.
Marine biodiversity collapse
Beyond coral bleaching, rising temperatures increase the risk of irreversible loss of coastal and marine ecosystems. These irremediable changes are already observable today, such as damaged mangrove forests and cold water species migrating to higher latitudes and altitudes. At a 1.1ºC increase in temperature today, approximately 60% of the world’s marine ecosystems have already been degraded or are being used unsustainably. Alarmingly, over half of the world’s marine species may become extinct by 2100, based on the latest estimates from the UN Educational, Scientific, and Cultural Organisation.
Rising sea levels
The rise of sea levels has accelerated in the last few years due to the melting of glaciers and ice sheets in the polar regions of the world. The World Meteorological Organisation found that the global mean sea level reached a new record high in 2023, rising by an average of 4.77 mm annually from 2014 to 2023—this is more than double the rate between 1993 and 2002.
Rising sea levels exacerbate extreme events, notably deadly storm surges and coastal hazards, including flooding, erosion, and landslides. Once centennial occurrences, extreme weather events are now forecasted to happen annually in many regions around the world. The Intergovernmental Panel on Climate Change (IPCC) has identified the areas most vulnerable to substantial sea-level rise: the western Tropical Pacific, the South-west Pacific, the North Pacific, the South-west Indian Ocean, and the South Atlantic. Currently, more than 680 million people, nearly 10% of the global population, live in low-lying coastal areas directly threatened by rising seas.
Conclusion: We must fight for our oceans
Despite these grim findings, all hope is not lost, with campaigners and conservationists devising systemic solutions to save our oceans. Acting upon these can play a major role in helping the world mitigate the worst effects of climate change, reducing global emissions by about 35%. Emission reductions of this magnitude are equivalent to four times the annual emissions of European Union countries, demonstrating the transformative potential of prioritising ocean-based climate actions.
A recent Ocean Panel study identified actions we can take:
- Scaling ocean-based renewable energy: Harness wind, tidal, and wave power to generate clean electricity and reduce fossil fuel dependence.
- Decarbonising ocean-based transport: Transition shipping to zero-emission vessels powered by hydrogen, ammonia, or batteries to cut the industry’s 3% share of global emissions.
- Conserving and restoring coastal and marine ecosystems: Protect mangrove forests, seagrass meadows, and coral reefs to sequester carbon, restore fisheries, and shield coastal communities.
- Utilising low-carbon food from the ocean: Develop sustainable aquaculture and algae-based proteins to feed populations while improving water quality and reducing emissions.
- Decarbonising ocean-based tourism: Adopt sustainable tourism practices, such as electric boats and low-impact accommodations, to protect marine environments.
- Reducing offshore oil and gas: Phase out fossil fuel extraction to prevent pollution and accelerate the transition to renewable energy.
These solutions are not isolated efforts, but interconnected strategies that reinforce one another. When implemented together at scale, they create a comprehensive framework for ocean recovery. The challenge now lies not in identifying what needs to be done, but in mobilising the political will, investment, and global cooperation required to implement these changes before irreversible damage to our ocean systems becomes inevitable.
Author: Eva Morisot