Soaring
ocean temperature is 'greatest hidden challenge of our generation'
IUCN
report warns that ‘truly staggering’ rate of warming is changing
the behaviour of marine species, reducing fishing zones and spreading
disease
Oliver Milman in
Honolulu
Monday 5 September
2016 19.00 BST
The soaring
temperature of the oceans is the “greatest hidden challenge of our
generation” that is altering the make-up of marine species,
shrinking fishing areas and starting to spread disease to humans,
according to the most comprehensive analysis yet of ocean warming.
The oceans have
already sucked up an enormous amount of heat due to escalating
greenhouse gas emissions, affecting marine species from microbes to
whales, according to an International Union for Conservation of
Nature (IUCN) report involving the work of 80 scientists from a dozen
countries.
The profound changes
underway in the oceans are starting to impact people, the report
states. “Due to a domino effect, key human sectors are at threat,
especially fisheries, aquaculture, coastal risk management, health
and coastal tourism.”
Dan Laffoley, IUCN
marine adviser and one of the report’s lead authors, said: “What
we are seeing now is running well ahead of what we can cope with. The
overall outlook is pretty gloomy.
“We perhaps
haven’t realised the gross effect we are having on the oceans, we
don’t appreciate what they do for us. We are locking ourselves into
a future where a lot of the poorer people in the world will miss
out.”
The scale of warming
in the ocean, which covers around 70% of the planet, is “truly
staggering”, the report states. The upper few metres of ocean have
warmed by around 0.13C a decade since the start of the 20th century,
with a 1-4C increase in global ocean warming by the end of this
century.
The ocean has
absorbed more than 90% of the extra heat created by human activity.
If the same amount of heat that has been buried in the upper 2km of
the ocean had gone into the atmosphere, the surface of the Earth
would have warmed by a devastating 36C, rather than 1C, over the past
century.
At some point, the
report says, warming waters could unlock billions of tonnes of frozen
methane, a powerful greenhouse gas, from the seabed and cook the
surface of the planet. This could occur even if emissions are
drastically cut, due to the lag time between emitting greenhouse
gases and their visible consequences.
Warming is already
causing fish, seabirds, sea turtles, jellyfish and other species to
change their behaviour and habitat, it says. Species are fleeing to
the cooler poles, away from the equator, at a rate that is up to five
times faster than the shifts seen by species on land.
Even in the north
Atlantic, fish will move northwards by nearly 30km per decade until
2050 in search of suitable temperatures, with shifts already
documented for pilchard, anchovy, mackerel and herring.
The warming is
having its greatest impact upon the building blocks of life in the
seas, such as phytoplankton, zooplankton and krill. Changes in
abundance and reproduction are, in turn, feeding their way up the
food chain, with some fish pushed out of their preferred range and
others diminished by invasive arrivals.
With more than 550
types of marine fishes and invertebrates already considered
threatened, ocean warming will exacerbate the declines of some
species, the report also found.
The movement of fish
will create winners and losers among the 4.3 billion people in the
world who rely heavily upon fish for sustenance. In south-east Asia,
harvests from fisheries could drop by nearly a third by 2050 if
emissions are not severely curtailed. Global production from capture
fisheries has already levelled off at 90m tonnes a year, mainly due
to overfishing, at a time when millions more tonnes will need to be
caught to feed a human population expected to grow to 9 billion by
2050.
Humans are also set
to suffer from the spread of disease as the ocean continues to heat
up. The IUCN report found there is growing evidence of vibrio
bacterial disease, which can cause cholera, and harmful algal bloom
species that can cause food poisoning. People are also being affected
by more severe, if not more numerous, hurricanes due to the extra
energy in the ocean and atmosphere.
Coral reefs, which
support around a quarter of all marine species, are suffering from
episodes of bleaching that have included three-fold in the past 30
years. This bleaching occurs when prolonged high temperatures cause
coral to expel its symbiotic algae, causing it to whiten and
ultimately die, such as the mass mortality that has gripped the Great
Barrier Reef.
Ocean acidification,
where rising carbon dioxide absorption increases the acidity of the
water, is making it harder for animals such as crabs, shrimps and
clams to form their calcium carbonate shells.
The IUCN report
recommends expanding protected areas of the ocean and, above all,
reduce the amount of heat-trapping gases pumped into the atmosphere.
“The only way to
preserve the rich diversity of marine life, and to safeguard the
protection and resources the ocean provides us with, is to cut
greenhouse gas emissions rapidly and substantially,” said Inger
Andersen, director general of the IUCN.
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