31 August 2019 | New Scientist | 41developed proposals for remotely operated
drone ships able to deliver the spray, which
he presented to the UK government’s
Environmental Audit Committee’s 2017
inquiry into Arctic sustainability. The thing
holding him back is lack of funding.For the price of Neymar
Shortly after I started corresponding with
Salter, he sent me a photo of Brazilian
footballer Neymar, beaming as his transfer to
Paris St Germain was announced in 2017 at a
cost to the French club of £198 million. Salter’s
point was made clear when he detailed the
costs of his cloud-seeding project. For the price
of Neymar, researchers could conduct all the
preliminary trials and then run an entire fleet
of ships for two years that might start to
restore the damage done to the Arctic.
“Among ideas to prevent Arctic collapse,
the most viable in terms of the scale and
nature of the problem involve increasing the
reflection of sunlight from the atmosphere,”
says Wanser, who is also an adviser to the
University of Washington’s Marine Cloud
Brightening Project. “However, our effective
level of investment in sunlight reflection
is zero. This leaves us with an enormous
exposure to near-term climate risk and
not enough fast-acting options to keep
warming within safe levels.” Several scientific
assessments have identified marine cloud
brightening as one of the most promising
methods to manage sunlight levels, says Rob
Wood at the University of Washington.
We don’t yet know how effective cloud
brightening might be. But there is another
reason to do this research: it could help
solve one of the biggest puzzles related
to how warm our planet could get (see
“Cloudbusting”, left).
In the meantime, the region continues to
turn from white to blue. Wadhams, who has
led 40 expeditions to the Arctic, has seen
enormous change in that time. “When I started
going to the Arctic, you could think of the
whole of the northern hemisphere as a solid
continent,” he says. “Ice connected Eurasia and
North America. But now you have blue ocean.
Physically and psychologically, the world is
fragmented, and I think that is having an
important change in how people think.” ❚Rowan Hooper (@rowhoop) is head of
features at New Scientist and author
of Superhuman: Life at the extremes
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AMCloudbusting
Predicting warming means deciphering the role of clouds
Clouds play a vital part in controlling our
climate. Their reflection of the sun’s rays,
especially at the tropics, is essential for
cooling Earth. But we don’t know how
cloud formation will change as the planet
gets hotter. This means we don’t know
how much warmer Earth will become
for a given increase in carbon dioxide
concentration in the air.
Climate change deniers often point out
that there is too much variability in the
predictions climate models make about
warming. One reason is a lack of certainty
about so-called climate sensitivity. This is
a measure of the amount of warming that
results from a doubling of carbon dioxide
in the atmosphere. In climate models, it
ranges from 2°C to 5°C.
We don’t know if our climate is
particularly sensitive – in that a doubling
of CO₂ gives a correspondingly large
increase in heating – or if it is resilient.
But Tapio Schneider, a climate scientist
at California Institute of Technology in
Pasadena, says evidence from improved
recent climate models points towards
the planet being more sensitive than we
thought, which means we should be very
worried. If it is that sensitive, then we will
get 1°C of additional warming from
adding a mere 70 parts per million or so of
CO₂ to the atmosphere – which would take
about 20 years at the current rate. That
would take us over 2°C of global warming
since pre-industrial times, the level atwhich “severe impacts” are expected:
more wildfires, longer periods of drought
in some regions and an increase in the
number and intensity of tropical storms.
Cloud formation is boosted by
atmospheric particles called aerosols,
many of which are pollutants from dirty
industrial processes and fossil fuels. As
these particles have a cooling effect on
the planet, both directly and through their
action on cloud formation, phasing out
their sources will unmask previously
concealed greenhouse gas warming. So to
understand the extra bump of warming
we can expect when the atmosphere gets
cleaner, we need to figure out how clouds
contribute to climate sensitivity.
“Marine cloud-brightening experiments
have the potential to shed light on one of
the most vexing and important questions
in climate science, namely how aerosols
affect clouds,” says Schneider. “It behooves
us to do everything we can to understand
the climate system better, before we try to
manipulate it.”promising potential intervention is one that
doesn’t involve tinkering with the ice directly.
Instead, it entails brightening the clouds over
the Arctic.
The idea dates back to the 1990s, when John
Latham, now at the University of Manchester,
UK, started thinking about ways of limiting
the greenhouse effect by reducing the amount
of sunshine reaching the planet’s surface.
Latham was fascinated by something called
the Twomey effect, which describes how the
amount of solar radiation that clouds reflect
back into space depends on the concentration
of tiny particles around which cloud droplets
form. He realised that you could increase this
concentration over oceans by seeding clouds
with tiny droplets of salt water.
We know from satellite images of ship
tracks – the equivalent of the contrails left by
airplanes – that clouds can be seeded by the
sulphate emissions from ships. Latham and his
colleagues have produced computer models
showing how Arctic sea ice may be restored
by brightening ocean stratocumulus clouds.
These large, rounded clouds are by far the
most common kind seen in the Arctic, and are
usually found in groups covering huge areas.
On paper, it looks promising, but testing it
for real is quite another matter. To do so will
require a system that can spray an ultra-fine
mist of sea water into the lower atmosphere
over a large area of ocean. Stephen Salter, an
engineer at the University of Edinburgh, UK,
has well-advanced plans for this, having