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Extreme
weather events such as wildfires and droughts will accelerate change in
stressed systems, leading to quicker tipping points of ecological
decline, according to a new study published today in Nature Sustainability.
The
research team used computer modelling to look at four ecosystems under
threat to work out what factors might lead to tipping points, beyond
which collapse would be inevitable.
In
some systems, the combination of adding new extreme events on top of
other ongoing stresses brought the timing of a predicted tipping point
closer to the present by as much as 80 per cent.
Stresses
Ultimately,
say the authors, a “perfect storm” of continuous stress from factors
such as unsustainable land use, agricultural expansion and climate
change, when coupled with disruptive episodes like floods and fires,
will act in concert to rapidly imperil natural systems. “Over a fifth of
ecosystems worldwide are in danger of collapsing,” said Professor Simon
Willcock, who co-led the study. “However, ongoing stresses and extreme
events interact to accelerate rapid changes that may well be out of our
control. Once these reach a tipping point, it’s too late.”
The
team looked at two lake ecosystems and two forestry examples, including
the historic collapse of the Easter Island (Rapa Nui) civilisation,
widely thought to have been the result of over-population combined with
unsustainable exploitation of tree cover.
The
models were run over 70,000 times for each ecosystem, with variables
adjusted on each occasion. Up to 15 per cent of collapses occurred as a
result of new stresses or extreme events, even while the main stress was
kept constant.
In
other words, even if ecosystems are managed more sustainably by keeping
the main stress levels like deforestation constant, new stresses like
global warming and extreme weather events could still bring forward a
collapse.
Tipping
The
number of extreme climate events has increased since 1980 and global
warming even at 1.5 °C will increase those numbers further. Scientists
are also concerned about possible knock-on effects as one collapsing
ecosystem impacts on neighbouring ecosystems.
“In
the past two years, the world has come together around the climate and
ecological crises through the UN Climate Change and Biodiversity
Conferences,” said Willcock. “But we should remember that the causes of
the crises are interlinked – that they have already collided – and that
inaction over both may result in dire consequences.”
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