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First described by the Intergovernmental Panel on Climate Change (IPCC) – the UN body tasked with advancing scientific knowledge about climate change – climate tipping points are critical thresholds which, when exceeded, can lead to significant, irreversible changes in the climate system.
“Many knowledge gaps remain with regards to these tipping points, notably their consequences for the marine ecosystem,” says Christoph Heinze, a biogeochemical ocean modeller at the University of Bergen, Norway, and project coordinator of the COMFORT project. “Our objective with COMFORT was to better understand what would happen when the tipping points are crossed and, most importantly, how we can limit the damage caused by abrupt, non-linear change.”
The COMFORT project team focused on three of the best known and most troubling consequences of climate change for marine ecosystems. The first is the warming of oceans, which drives the loss of sea ice, increases sea levels and causes shifts in local habitats. The second is ocean acidification, where dissolved carbon dioxide reduces pH levels, and can interfere with the ability of corals and shellfish to make their shells. And the final one is deoxygenation, where natural and induced conditions can result in bodies of water that have no dissolved oxygen, and are uninhabitable for fish . Experts commonly refer to these as the “triple threat” to oceans, as their combination increases the likelihood of oceans reaching irreversible tipping points.
The team – comprising ocean physicists, biogeochemists and ecologists – used data analysis and predictive models to project the impact of human drivers on ocean systems. “With this integrative method, we could obtain a more comprehensive understanding of the ocean’s response to climate change,” notes Heinze.
The need to act now
Their findings are alarming, pointing to an emerging climate feedback loop that is accelerating sudden, permanent change in marine environments. “Our predictions imply abrupt changes and regime shifts in the oceans, which critically affect marine species and ecosystems.”
The team identified a rash of sudden changes that have occurred in multiple oceanic provinces. These include sharp rises in the frequency of extreme events such as marine heatwaves, sudden seasonal acidification events, and temporary drawdown of oxygen, all of which can inflict long-lasting shock-induced ecosystem shifts.
COMFORT’s findings indicate that some flexibility remains to avert the worst impacts of the changes, and offer insight for policymakers into the best strategies for proactive and decisive remediation measures. These could include large-scale carbon dioxide removal, and the selection of marine protected areas similar to national parks and nature reserves on land.
These could be effective if combined with curbs on nutrient pollution from fertiliser run-off and industry, plastic litter and overfishing, says Heinze, although the key measure to be tackled is rising levels of carbon dioxide. “We need a drastic reduction in greenhouse emissions,” he adds. “It’s much better and more cost-effective to do it now rather than hoping that potential future geoengineering solutions will solve some of our problems.”
Even so, some changes are unavoidable. Substantial and immediate reductions in greenhouse gas emissions would only slow the loss of Arctic Sea ice and the weakening of the Gulf Stream, but not stop it, while the triple threat of rising temperatures and falling ocean pH and oxygen levels would persist over millennia.
Time to turn the wheel
The findings underscore the urgent need for the whole international community to work in unison. The COMFORT project generated a large number of scientific publications and has made significant contributions to the IPCC’s latest Assessment Report (IPCC AR6).
With the project completed, its members continue their work on other climate-related investigations worldwide. “There is a major need for extended ocean observations, along with improved observational networks and Earth system models to enhance our understanding of oceanic processes,” Heinze explains. “I also think there should be a task force giving more concrete policy advice based on the knowledge we already have. How can we help to steer through the climate crisis with the least damage, so that life remains a worthwhile adventure? There is not much time and the wheel has to be turned around now.”