Until recently, you might be forgiven for thinking the oceans were a trivial component of Earth’s climate system, and that the consequences of change were minimal. After all, only 5% of papers published on climate change involve ocean systems. The Intergovernmental Panel on Climate Change (IPCC), which evaluates the peer-reviewed scientific literature, did not devote a regional chapter to the ocean until its most recent major report.
Yet the ocean system could not be more important: it regulates the global temperature and atmosphere, feeds 3 billion people, and largely determines our weather. The ocean also has lots of “inertia” – which means getting the ocean to change takes a lot of energy, but once it begins to change, slowing it down becomes more or less impossible.
A paper published last week in Science, of which I am one of the authors, has issued a warning that our window of opportunity to save the oceans from major changes is in danger of slamming shut, bringing with it the risk we will encounter planetary-scale tipping points in the behaviour of the climate. Building on the IPCC’s extensive assessment last year of the effects of climate change on the oceans, my co-authors and I have compiled the latest evidence and projections about the ocean under rapid human-driven climate change.
The news is not good. Failure to act on climate change will see warmer and more stagnant oceans, with declining oxygen levels and productivity in some regions, and the removal or modification of ecosystems in other areas. Fisheries and national economies are in the crosshairs in many regions. Rising seas and intensifying storms, plus a loss of critical coastal features, will make life on the shores of a rapidly changing ocean dangerously different to today.
The latest is Pope Francis, who became the first pontiff to warn of ocean warming, acidification and sea-level rise, pointing out in his recent encyclical that “a quarter of the world’s population lives on the coast or nearby, and … the majority of our megacities are situated in coastal areas”.
Our research adds to the mounting evidence that these leaders are right when they say we need to act decisively on fossil fuel emissions and other drivers of climate change.
One of the most stunning conclusions from the IPCC’s report is the statement that “the current rate and magnitude of ocean acidification are at least ten times faster than any event within the last 65 million years”. Given that periods of rapid acidification over tens of thousands of years – slow by our current human-driven standard – resulted in mass extinction and ecological collapse, this alone should be reason to act.
In a few regions, such as the North Sea, temporary increases in fisheries production are being reported, as the ice retreats, seas warm, and productivity increases. But these benefits are few and far between, and are likely to disappear over time as the ocean warms and acidifies further.
Coral reefs perhaps provide the perfect parable for the Pope’s encyclical. Everyone appreciates their beauty and value, but few may be aware of the crucial role they play in terms of protecting coastlines, and supporting fisheries and other industries. They generate hundreds of billions of dollars each year and support some 500 million – mostly impoverished – people worldwide. Our report highlights the extreme sensitivity of these ecosystems to ocean warming and acidification.