Engineering our way out of global
climate warming may not be as easy as simply reducing the incoming solar
energy, according to a team of University
of Bristol and Penn State University climate scientists. Designing
the approach to control both sea level rise and rates of surface air
temperature changes requires a balancing act to accommodate the diverging needs
of different locations.
“Basic physics and past
observations suggest that reducing the net influx of solar energy will cool the
Earth,” said Peter J. Irvine, graduate student, University
of Bristol, U.K.,
and participant in the Worldwide Universities Network Research Mobility
Programme to Penn
State. “However,
surface air temperatures would respond much more quickly and sea levels will
respond much more slowly.”
Current solar radiation
management approaches include satellites that block the sun, making the Earth’s
surface more reflective or mimicking the effects of volcanoes by placing
aerosol particles in the upper atmosphere.
“These solar radiation
management approaches could be cheaper than reducing carbon dioxide
emissions,” said Klaus Keller, associate professor of geosciences, Penn State.
“But they are an imperfect substitute for reducing carbon dioxide
emissions and carry considerable risks.”
How well they work at reducing
sea level rise or surface air temperatures depends on how they are implemented.
“Strategies designed to
reverse sea-level rise differ from the strategies designed to limit the rate of
temperature changes,” said Ryan Sriver, research associate in geosciences,
Penn State.
To stop or reverse sea-level
rise, the incoming solar radiation would have to be decreased rapidly, but this
approach would produce rapid cooling. Adopting a more gradual approach would
reduce the risks due to rapid cooling, but would allow for considerable
sea-level rise.
The researchers note that people
living close to sea level are likely more concerned about sea-level rise than
about the rates of surface temperature changes. In contrast, those living far
from the oceans, are likely more concerned about rates of surface temperature
changes that can influence agricultural or energy usage.
The researchers used a model to
analyze the tension between controlling sea-level rise and rates of surface
temperature changes. They ran 120 scenarios with differing combinations of
solar radiation management (SRM) including one called “business as
usual,” which has no SRM.
They note that their model
includes many approximations. For example, it does not include a mechanistic
representation of ice sheets. They also did not consider scenarios that combine
solar radiation management and reducing carbon dioxide emissions.
They report in Nature Climate Change that the forcing
required to stop sea-level rise could cause a rapid cooling with a rate similar
to the peak business-as-usual warming rate.
“While abrupt cooling may
sound like a good idea, it could be more damaging than the increasing
temperatures caused by increasing carbon dioxide,” said Keller.
“The rate of cooling can be
a problem if it exceeds the capacity of the plants and animals to adapt,”
said Sriver.
Another consideration when
implementing solar radiation management approaches is that these approaches can
require a long-term commitment. The researchers showed that “termination
of solar radiation management was found to produce warming rates up to five
times greater than the maximum rates under the business-as-usual scenario,
whereas sea-level rise rates were only 30% higher.”
To avoid such harsh changes,
should SRM be discontinued, requires a slow phase out over many decades. This
places a commitment on future generations.
