Even
though it sounds like science fiction, researchers are taking a second
look at a controversial idea that uses futuristic ships to shoot salt
water high into the sky over the oceans, creating clouds that reflect
sunlight and thus counter global warming.
University
of Washington atmospheric physicist Rob Wood describes a possible way
to run an experiment to test the concept on a small scale in a
comprehensive paper published this month in the journal Philosophical Transactions of the Royal Society.
The
point of the paper—which includes updates on the latest study into what
kind of ship would be best to spray the salt water into the sky, how
large the water droplets should be and the potential climatological
impacts—is to encourage more scientists to consider the idea of marine
cloud brightening and even poke holes in it. He and a colleague detail
an experiment to test the concept.
“What
we’re trying to do is make the case that this is a beneficial
experiment to do,” Wood said. With enough interest in cloud brightening
from the scientific community, funding for an experiment may become
possible, he said.
The
theory behind so-called marine cloud brightening is that adding
particles, in this case sea salt, to the sky over the ocean would form
large, long-lived clouds. Clouds appear when water forms around
particles. Since there is a limited amount of water in the air, adding
more particles creates more, but smaller, droplets.
“It
turns out that a greater number of smaller drops has a greater surface
area, so it means the clouds reflect a greater amount of light back into
space,” Wood said. That creates a cooling effect on Earth.
Marine
cloud brightening is part of a broader concept known as geoengineering
which encompasses efforts to use technology to manipulate the
environment. Brightening, like other geoengineering proposals, is
controversial for its ethical and political ramifications and the
uncertainty around its impact. But those aren’t reasons not to study it,
Wood said.
“I
would rather that responsible scientists test the idea than groups that
might have a vested interest in proving its success,” he said. The
danger with private organizations experimenting with geoengineering is
that “there is an assumption that it’s got to work,” he said.
Wood
and his colleagues propose trying a small-scale experiment to test
feasibility and begin to study effects. The test should start by
deploying sprayers on a ship or barge to ensure that they can inject
enough particles of the targeted size to the appropriate elevation, Wood
and a colleague wrote in the report. An airplane equipped with sensors
would study the physical and chemical characteristics of the particles
and how they disperse.
The
next step would be to use additional airplanes to study how the cloud
develops and how long it remains. The final phase of the experiment
would send out five to 10 ships spread out across a 100 km, or 62 mile,
stretch. The resulting clouds would be large enough so that scientists
could use satellites to examine them and their ability to reflect light.
Wood
said there is very little chance of long-term effects from such an
experiment. Based on studies of pollutants, which emit particles that
cause a similar reaction in clouds, scientists know that the impact of
adding particles to clouds lasts only a few days.
Still,
such an experiment would be unusual in the world of climate science,
where scientists observe rather than actually try to change the
atmosphere.
Wood
notes that running the experiment would advance knowledge around how
particles like pollutants impact the climate, although the main reason
to do it would be to test the geoengineering idea.
A
phenomenon that inspired marine cloud brightening is ship trails:
clouds that form behind the paths of ships crossing the ocean, similar
to the trails that airplanes leave across the sky. Ship trails form
around particles released from burning fuel.
But in some cases ship trails make clouds darker. “We don’t really know why that is,” Wood said.
Despite increasing interest from scientists like Wood, there is still strong resistance to cloud brightening.
“It’s
a quick-fix idea when really what we need to do is move toward a
low-carbon emission economy, which is turning out to be a long process,”
Wood said. “I think we ought to know about the possibilities, just in
case.”
The authors of the paper are treading cautiously.
“We
stress that there would be no justification for deployment of [marine
cloud brightening] unless it was clearly established that no significant
adverse consequences would result. There would also need to be an
international agreement firmly in favor of such action,” they wrote in
the paper’s summary.
There
are 25 authors on the paper, including scientists from University of
Leeds, University of Edinburgh and the Pacific Northwest National
Laboratory. The lead author is John Latham of the National Center for
Atmospheric Research and the University of Manchester, who pioneered the
idea of marine cloud brightening.
Source: University of Washington
