Risks of 'domino effect' of tipping points greater than
thought, study says
Scientists warn policymakers not to ignore links, and stress
that ‘every action counts’
Jonathan Watts
Thu 20 Dec 2018 19.00 GMT Last modified on Thu 20 Dec 2018
19.01 GMT
When arctic ice melts, less sunlight is reflected, which
raises global temperatures and increases the risk of forest fires. Photograph:
Mario Tama/Getty Images
Policymakers have severely underestimated the risks of
ecological tipping points, according to a study that shows 45% of all potential
environmental collapses are interrelated and could amplify one another.
The authors said their paper, published in the journal
Science, highlights how overstressed and overlapping natural systems are
combining to throw up a growing number of unwelcome surprises.
“The risks are
greater than assumed because the interactions are more dynamic,” said Juan
Rocha of the Stockholm Resilience Centre. “The important message is to
recognise the wickedness of the problem that humanity faces.”
The study collated existing research on ecosystem
transitions that can irreversibly tip to another state, such as coral reefs
bleaching and being overrun by algae, forests becoming savannahs and ice sheets
melting into oceans. It then cross-referenced the 30 types of shift to examine
the impacts they might have on one another and human society.
Only 19% were entirely isolated. Another 36% shared a common
cause, but were not likely to interact. The remaining 45% had the potential to
create either a one-way domino effect or mutually reinforcing feedbacks.
Among the latter pairings were Arctic ice sheets and boreal
forests. When the former melt, there is less ice to reflect the sun’s heat so
the temperature of the planet rises. This increases the risks of forest fires,
which discharge carbon into the air that adds to the greenhouse effect, which
melts more ice. Although geographically distant, each amplifies the other.
By contrast, a one-way domino-type impact is that between
coral reefs and mangrove forests. When the former are destroyed, it weakens
coastal defences and exposes mangroves to storms and ocean surges.
The deforestation of the Amazon is responsible for multiple
“cascading effects” – weakening rain systems, forests becoming savannah, and
reduced water supplies for cities like São Paulo and crops in the foothills of
the Andes. This, in turn, increases the pressure for more land clearance.
Until recently, the study of tipping points was
controversial, but it is increasingly accepted as an explanation for climate
changes that are happening with more speed and ferocity than earlier computer
models predicted. The loss of coral reefs and Arctic sea ice may already be
past the point of no return. There are signs the Antarctic is heading the same
way faster than thought.
Co-author Garry Peterson said the tipping of the west
Antarctic ice shelf was not on the radar of many scientists 10 years ago, but
now there was overwhelming evidence of the risks – including losses of chunks
of ice the size of New York – and some studies now suggest the tipping point
may have already been passed by the southern ice sheet, which may now be
releasing carbon into the atmosphere.
“We’re surprised at the rate of change in the Earth system.
So much is happening at the same time and at a faster speed than we would have
thought 20 years ago. That’s a real concern,” said Peterson. “We’re heading
ever faster towards the edge of a cliff.”
The fourth most downloaded academic research of 2018 was the
Hothouse Earth paper, which considered how tipping points could combine to push
the global climate into an uninhabitable state.
The authors of the new paper say their work goes beyond
climate studies by mapping a wider range of ecological stress points, such as
biodiversity loss, agricultural expansion, urbanisation and soil erosion. It
also focuses more on what is happening at the local level now, rather than
projecting geo-planetary trends into the future.
“We’re looking at things that affect people in their daily
lives. They’re things that are happening today,” said Peterson. “There is a
positive message as it expands the range of options for action. It is not just
at an international level. Mayors can also make a difference by addressing soil
erosion, or putting in place social policies that place less stress on the
environment, or building up natural coastal defences.”
Rocha has spent 10 years building a database of tipping
points, or “regime shifts” as he calls them. He urges policymakers to adopt a
similar interdisciplinary approach so they can better grasp what is happening.
“We’re trying to connect the dots between different research
communities,” said Rocha. “Governments also need to look more at interactions.
They should stop compartmentalising ministries like agriculture, fisheries and
international relations and try to manage environmental problems by embracing
the diversity of causes and mechanisms underlying them. Policies need to match
the scale of the problem.
“It’s a little depressing knowing we are not on a trajectory
to keep our ecosystem in a functional state, but these connections are also a
reason for hope; good management in one place can prevent severe environmental
degradation elsewhere. Every action counts.”
Sem comentários:
Enviar um comentário