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Ocean and coastal species and habitats are struggling with a rapid shift to conditions that haven’t been seen in thousands of years, the Intergovernmental Panel on Climate Change (IPCC) reports in this week’s assessment of climate adaptation, impacts, and vulnerability.
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“Anthropogenic climate change has exposed ocean and coastal ecosystems to conditions that are unprecedented over millennia,” and these factors have “greatly impacted” life in the ocean and along the coasts, the IPCC writes. Surface warming in the last half century has shifted marine species towards the poles at 60 kilometres per decade, while seasonal events for fish occur three days earlier per decade.
Covering 71% of the globe, oceans provide animal protein for 3.3 billion people and livelihoods for 60 million. They regulate global climate, sequester anthropogenic atmospheric CO2, produce half the world’s photosynthetic oxygen, and provide a wealth of aesthetic and cultural resources, although the report does not quantify the economic benefits from tourism or other ocean industries.
Warming, acidification, and deoxygenation are increasing the threat to fish and invertebrates which, in turn, drives habitat loss and population declines. “At warming levels beyond 2°C by 2100, risks of extirpation, extinction, and ecosystem collapse escalate rapidly,” the report warns, and extreme global warming levels of greater than 5.2°C may cause mass extinction of marine species.
Marine heat waves are more frequent and intense, which “exposes species and ecosystems to environmental conditions beyond their tolerance and acclimation limits.” These heat waves are responsible for mass mortalities among coral reefs, rocky shores, kelp forests, seagrasses, mangroves, and semi-enclosed seas, as well as recent events along the west coast of North America and the east coast of Australia which “drive abrupt shifts in community composition that may persist for years.”
As reefs, kelp forests, and seagrass meadows undergo irreversible phase shifts, marine habitats will collapse. Without adaptation, the report says “the rate of sea level rise is very likely to exceed that of reef growth by 2050,” and altered timing of plankton blooms increases the risk of a mismatch with fish spawning seasons.
“Although impacts of multiple climate and non-climate drivers can be beneficial or neutral to marine life, most are detrimental,” the report warns, and warming worsens the severe impacts from “dead zones” or low oxygen areas in oceans. Overfishing and urbanization also increase the vulnerability of coastal ecosystems to sea level rise and changes in wave energy, but the report suggests humans have the means to reduce their pressure on ecosystems that will decrease their vulnerability.
“Climate-driven impacts on ocean and coastal environments have caused measurable changes in specific industries, economic losses, emotional harm, and altered cultural and recreational activities around the world,” and these impacts are increasing the geographic spread and risk of marine-borne pathogens which endanger human health, the IPCC says. Both climatic and non-climate factors expose densely-populated coastal zones to flooding and decrease physical protection of people, property, and culturally important sites.
It is virtually certain that ocean conditions will continue to diverge from a pre-industrial state as a result of climatic drivers, the authors add. Even if average warming remains below 2°C, the richness of marine species near the equator and in the Arctic will continue to decline. Even in the deep ocean, “all global warming levels will cause faster movements of temperature niches by 2100 than those that have driven extensive reorganization of marine biodiversity at the ocean surface over the past 50 years.”
Risks from sea level rise for coastal ecosystems and people “are very likely to increase tenfold well before 2100 without adaptation and mitigation action,” the IPCC says. Sea level rise will increase the risk of coastal erosion and loss of coastal habitat, while salinization of groundwater will compromise coastal ecosystems and livelihoods.
Without major efforts to reduce emissions and adapt to climate impacts, “most coral reefs, mangroves, and salt marshes will be unable to keep up with sea level rise by 2050,” and ecological impacts will escalate rapidly beyond that time, and resulting decreases in natural shoreline protection will place increasing numbers of people at risk. “The ability to adapt to current coastal impacts, cope with future coastal risks, and prevent further acceleration of sea level rise beyond 2050 depends on immediate implementation of mitigation and adaptation actions,” the report warns.
New studies and model simulations are providing evidence of how changing climate effects oceans, as well as how human communities experience these impacts.
Climate change will alter many ecosystem services, the IPCC finds, but the impacts on humans will depend on the overall vulnerability of each community, which is strongly influenced by local context and development pathways. The report suggests fishers will be less vulnerable if they are able to move, diversify, or leverage technology to sustain harvests, while rules to eliminate overfishing will increase the future capacity of fisheries to adapt. Communities that depend on marine resources, including Indigenous Peoples, will be at increased risk of losing cultural heritage and traditional seafood-sourced nutrition.
Early warning systems and public education about environmental change, developed and delivered within local and cultural contexts, can decrease those risks, the report notes. Humans are already adapting to climate-driven changes in marine systems, and while more adaptation will be required even under low-emission scenarios, transformative adaptation will be essential if emissions exceed that minimum.
“Without transformation, global inequities will likely increase between regions and conflicts between jurisdictions may emerge and escalate,” the report states.
Ultimately, while “available adaptation options are unable to offset climate change impacts on marine ecosystems” the IPCC says, transformative adaptation combined with ambitious and urgent mitigation measure, “can meaningfully reduce impacts.” Marine protected areas can contribute substantially to adaptation and mitigation if they are designed to address climate change, strategically implemented, and well governed.
But “climate change has caused substantial damages, and increasingly irreversible losses, in terrestrial, freshwater, and coastal and open ocean marine ecosystems,” the section concludes. “The extent and magnitude of climate change impacts are larger than estimated in previous assessments,” with adverse socioeconomic consequences. And at this point, “some losses are already irreversible” while other impacts “are approaching irreversibility.”
