Almost three quarters of the world’s oceans will experience a radical reordering of biodiversity the likes of which have not been seen in 3 million years, if the world’s governments do not succeed in keeping global warming below 2C, according to new research.
A study appearing in the journal Nature Climate Change this week used models to compare the distribution of marine biodiversity from three key periods in the Earth’s history to reconstruct historical large-scale patterns of biodiversity changes. The first, known as the Mid-Pliocene (roughly four million years ago) is crucially important for climate scientists, as it was the most recent time when average global temperatures were significantly warmer than the pre-industrial era for an extended period. In addition, the Pilocene epoch is sufficiently recent that the continents and ocean basins were little different to their present-day arrangement, making it a great example for us to explore what the late 21st Century could look like.
The second period the scientists looked at was the Last Glacial Maximum (LGM)—some 26-20,000 years ago, when ice sheets extended their furthest over the globe. And finally, the researchers considered the period from 1960-2013, when anthropogenic global warming began to spike. They then projected forward under various warming scenarios up to the end of this century trends and patterns they had spotted across the three periods.
The good news is that under a warming scenario in which we manage to keep below 2°C, with emissions peaking and then declining before 2020, changes to marine biodiversity may be relatively benign, and little different to the annual variability recorded since the sixties.
But current trends suggest that we will not keep within the 2°C limit. Instead, we are on track to hit 4.8°C of warming above pre-industrial levels by 2100. And so without aggressive action to mitigate emissions, at nearly 5°C of warming by century’s end, between 50 and 70 percent of the world’s oceans will experience a massive turnover in biodiversity akin to or even greater than that experienced between the LGM or mid-Pliocene and today.
For scenarios around two and a half degrees of warming, the rearrangement of biodiversity should actually lead to a boost in average local biodiversity as increases as a result of ‘invasion’ from species from elsewhere exceed the losses resulting from local extinction. At high levels of warming, however, the situation reverses.
The paper comes during the same week that a report was published from the Canadian Parks and Wilderness Society suggesting that the extent of Canada’s marine protected areas is far less than that of the US or Britain. The report notes that as species are threatened by ocean warming and acidification, zones set aside by provincial and federal legislation for species and habitat conservation become increasingly important. The CPAWS report says that just 0.11 percent of Canada’s ocean territory is fully closed to industries such as fishing and oil and gas extraction. The US and UK meanwhile maintain marine conservation zones that cover close to 10 percent of their ocean territory.
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