Great Barrier Reef Faces “Existential” Danger from Global Heating, Study Finds
New scientific warning that ocean temperatures are hottest in 400 years comes in wake of an international court determining that GHG emissions constitute marine pollution.
Anthropogenic global heating poses an “existential threat” to the Great Barrier Reef, scientists warn in a new study that finds that this natural wonder has in recent years simmered in ocean temperatures that have been at their highest in 400 years.
This observed warming, the researchers say, is undoubtedly due to human activities – primarily fossil fuel consumption – that release heat-trapping pollution, much of which is absorbed by the oceans. Coral reefs can become heat-stressed under elevated temperatures, resulting in coral bleaching whereby the corals expel their symbiotic algae and turn into eerie white skeletons. Sometimes reefs can recover, but as oceans continue to heat up and bleaching events become more frequent, these marine ecosystems could be facing permanent deterioration.
Limiting global heating to 1.5°C above preindustrial levels (current warming is around 1.2°C) would likely lead to the loss of 70 to 90 percent of the world’s corals, and allowing heating to rise above 2°C, the researchers warn, “would have disastrous consequences for coral ecosystems and the hundreds of millions of people who currently depend on them.”
Failing to rein in greenhouse gas emissions that cause global heating, and continuing on the current business-as-usual trajectory, is basically a death sentence for the Great Barrier Reef, which is “at risk of experiencing temperatures conducive to near-annual coral bleaching, with negative consequences for biodiversity and ecosystems services.” That’s according to a study from scientists at Australian universities, published August 7 in the journal Nature, titled “Highest ocean heat in four centuries places Great Barrier Reef in danger.”
The Great Barrier Reef, stretching over 1,400 miles off the coast of northeastern Australia, is the world’s largest living structure.
I visited part of the Great Barrier Reef during a semester abroad in Australia in 2011, and even back then the corals were showing signs of bleaching.
But it is increasingly vulnerable to marine heatwaves and stresses from anthropogenic climate change. The reef has experienced five mass bleaching events since 2016, which coincide with five of the warmest years in terms of sea surface temperatures in the Coral Sea over the past 400 years, the study finds. “The mass coral bleaching years of 2016, 2017, 2020, 2022 and 2024, and the heat event of 2004, stand out as the warmest events across the whole 407-year record,” the new study states.
The outlook for the Great Barrier Reef is grim, as the researchers say that corals are unlikely to be able to adapt fast enough to keep pace with accelerated global heating.
“In the absence of rapid, coordinated and ambitious global action to combat climate change, we will likely witness the demise of one of Earth’s great natural wonders,” the study concludes.
“The Great Barrier Reef is facing catastrophe if anthropogenic climate change is not immediately addressed. The very corals that have lived for hundreds of years and that gave us the data for our study are themselves under serious threat,” Helen McGregor, professor at the University of Wollongong and study co-author, said in a news release.
“Without urgent intervention, our iconic Great Barrier Reef is at risk of near-annual bleaching from high ocean temperatures. The Reef’s fundamental ecological integrity and outstanding universal value are at stake,” said Benjamin Henley, the study’s lead author and a lecturer at the University of Melbourne.
“We can never lose hope. Every fraction of a degree of warming we avoid will lead to a better future for the human and natural systems of our planet,” Henley added. “We hope that our study equips policymakers with more evidence to pursue deeper cuts in greenhouse gas emissions internationally.”
“Tides Change”
Current policies and promises from countries to reduce these emissions are not aligned with the internationally agreed-upon goals of the Paris Climate Agreement to limit global heating to well below 2°C and to pursue efforts to prevent temperature rise above 1.5°C. According to the UN Environment Programme’s 2023 Emissions Gap report, the world is on track for a 2.5-2.9°C temperature rise this century, underscoring the urgent need for steep emissions reductions this decade if the Paris Agreement goals are to have any chance of being realized.
In May, the International Tribunal for the Law of the Sea (ITLOS), considered as a kind of world oceans court, delivered a landmark advisory opinion clarifying that countries have legal obligations to take all necessary measures to reduce anthropogenic greenhouse gas emissions. Such emissions, the Tribunal found, constitute a form of pollution of the marine environment. The Tribunal’s finding is based on the best available science including the reports of the Intergovernmental Panel on Climate Change (IPCC), which clearly indicate that climate change driven by rising GHG emissions produces multiple deleterious effects on the oceans. Countries therefore have duties under international ocean law to reduce and control pollution of the marine environment from anthropogenic GHG emissions and to protect marine environment habitat and other threatened forms of marine life from the effects of climate change, according to the ITLOS advisory opinion.
The opinion interpreted the scope of state duties under a 1982 ocean treaty called the UN Convention on the Law of the Sea, which 169 countries are party to. The United States is not formally party to the Convention.
The US, of course, is the world’s largest historical emitter of greenhouse gases and currently the second biggest global climate polluter, and the top oil and gas producer. Yet, holding the US accountable for its significant contribution to the climate problem under international or even domestic law seems to be extremely difficult. Should former president Donald Trump retake the White House in the upcoming election, the US is expected to pull back out of the Paris Agreement and may even try to exit the UN Framework Convention on Climate Change (UNFCCC).
I noted this context in a question I raised during a webinar last month on the ITLOS climate change advisory opinion, asking what impact such an opinion from an international tribunal – which is nonbinding anyway – might have on the policies and decisions of the US. Since the US is not a signatory to UN ocean treaty and not formally subject to decisions from ITLOS, it seems that the advisory opinion would have little if any impact.
Joie Chowdhury, a senior attorney at the Center for International Environmental Law and one of the panelists on the webinar, acknowledged that the US is in a tough spot with the looming threat of authoritarianism and hostility to climate and environmental protection coming from the country’s highest domestic court.
“The US right now is in such a difficult space, the Supreme Court is in such a difficult space,” she said, “but tides change and we can keep fighting and we can keep doing what we can.”