Tipping points not backed by science
The scientists, from America, Australia and Britain, argue that global-scale ecological tipping points are unlikely and that ecological change over large areas seems to follow a smoother, more gradual pattern.
They dismiss recent efforts to define 'planetary tipping points' – critical levels of biodiversity loss or land-use change that would have a global impact – saying their argument has important implications for science and policy-makers.
"This is good news because it says we might avoid the doom-and-gloom scenario of abrupt, irreversible change," says Professor Barry Brook, lead author of a paper published in the journal Trends in Ecology & Evolution.
"A focus on planetary tipping points may both distract from the vast ecological transformations that have already occurred, and lead to unjustified fatalism about the catastrophic effects of tipping points,” says Brook, director of climate change at the University of Adelaide.
The ecologists say an emphasis on a point of no return is not particularly helpful in generating the conservation action needed. The efforts to reduce human impacts on the global ecology must continue but without undue attention to trying to avoid “arbitrary thresholds".
A tipping point occurs when an ecosystem attribute such as species abundance or carbon sequestration responds rapidly and possibly irreversibly to a human pressure such as land-use change or climate change. Many local and regional-level ecosystems, including lakes and grasslands, are known to behave this way.
According to the team, a planetary tipping point could theoretically occur if ecosystems across Earth responded in similar ways to the same human pressures, or if there were strong connections between continents that allowed for rapid diffusion of impacts across the planet.
But the ecologists say these criteria are highly unlikely to be met “in the real world" because ecosystems on different continents are not strongly connected. Likewise, the responses of ecosystems to human pressures, such as climate change or land-use change, depend on local circumstances and will therefore differ between localities.
In their study, the scientists examined four principal drivers of terrestrial ecosystem change: climate change, land-use change, habitat fragmentation and biodiversity loss. They found each of these was unlikely to induce global tipping points.
The co-author of the paper, Associate Professor Erle Ellis from the US University of Maryland in Baltimore County, says as much as four-fifths of the biosphere is today characterised by ecosystems that locally, over centuries and millennia, have undergone human-driven regime shifts of one or more kinds.
“Recognising this reality and seeking appropriate conservation efforts at local and regional levels might be a more fruitful way forward for ecology and global change science," Ellis says.