Dispersing
fine (sub-micron) light-scattering particles into the upper atmosphere
could help to combat climate change, suggests a former U.K. government
advisor and chemical engineer.
The
technology concept developed in the U.K. advocates dispersing benign
titanium dioxide particles as used in paint, inks and sunscreens into
the stratosphere to deflect the sun’s rays. In a tce webinar on 15 May,
Peter Davidson, a Chartered Chemical Engineer, Fellow of IChemE and the
Royal Academy of Engineering, and a former senior innovation advisor to a
number of government departments, will call for this geoengineering
concept to be researched as an insurance policy to cope with possible
catastrophic effects of global warming if we don’t manage to reduce CO2
emissions fast enough.
“While
it’s essential that we work to reduce carbon dioxide emissions now, it
would be wise to have a well-researched emergency system in reserve as a
Plan B,” says Davidson.
The
idea may sound like science fiction; but the concept in fact mimics the
earth-cooling effects of large volcanic eruptions which occur several
times a century. When in 1991 Mount Pinatubo erupted in the Philippines,
it caused temperatures to drop by around 0.5 C around the globe for two
years, ending most talk of global warming during this period.
The
eruption threw 20 million tons of sulphur dioxide into the
stratosphere, forming a fine mist of sulphuric acid particles that
spread over the globe in a matter of months.
As
the size of volcanic aerosol particles is similar to the wavelength of
sunlight, they scattered a small proportion of the light (~1 %), and
hence its heat back into space. The Earth cooled.
Adding
sulphuric acid to the stratosphere degrades the ozone layer, and may
cause regional changes in precipitation. We need a benign but similarly
sized particle; Davidson suggests titanium dioxide (TiO2), mankind’s
most commonly-used pigment. It is stable in air, non-toxic and
seven-times more effective at scattering light than sulphuric acid.
Titanium is abundant in the earth’s crust and five million tonnes a year
of pigment is produced currently so supply appears feasible. If you are
reading this on a printed page the ink and the paper probably both have
a TiO2 pigment in them.
With
a candidate particle identified, the next challenge is devising a
system to effectively and economically lift and disperse millions of
tons of particles some 20 km (about 65,000 feet) up into the
stratosphere, so they stay up for a couple of years and do not
immediately get rained out.
Davidson
says: “The impact of global warming is predicted to be most severe on
the world’s poorest peoples, both because of their lack of resources and
because of where they happen to be living. I would hope we could ensure
that these peoples have a stake in decision-making and the opportunity
to have their voice heard, alongside the richer countries, and
appropriate NGO’s (for example environmentalists), as well as other
bodies.
“Ideally
an independent charitable trust funded by a variety of stakeholders
from around the world would research not only the technology but
suitable governance, legal and ethical frameworks,” adds Davidson.
The
total capital cost of the balloon, tethers, ultra high pressure pumps,
and the production and transport of the particles is estimated to be
£500m plus £600m in annual operating costs in a paper to be published by
the Royal Society. These costs are perhaps thirty times lower than the
next best technologies considered, such as large numbers of very
sophisticated jet aircraft, and do not have the same carbon footprint.
“Space mirrors on the scale needed and 20km tall towers are likely to be for the 22nd century not this one,” says Davidson.
Very
approximate estimates are that we’d need to disperse over a million
tonnes of titanium dioxide per year to keep planetary temperatures
constant if CO2 levels in the atmosphere double. If such an insurance
policy was needed we would have to do this for 50 to 150 years. Ocean
acidification would be a worry but this might be still worse if such
temperature control did not keep methane emissions from melting arctic
tundra or seas under control.
At current U.K. prices, supplying these particles would cost around £3bn per year or around 50p per person per year.
Davidson
says: “Creating a suitable insurance policy for climate remediation is
a vital task. It will not do to underestimate the challenges. Much
research and work on governance is still needed, but a vision is now on
offer for debate, and development where potential means of solving some
of the most difficult technical challenges have been identified. It
would be short-sighted to put-off research of such a safety-device—like
trying to develop a life-jacket when you’re swept out to sea and
struggling in the water.”
Source: IChemE
