ISIS Report 23/07/12
Unintended Hazards of Geoengineering
Reducing the solar radiation
that reaches Earth will have potentially significant consequences beyond limiting
the mean temperature of the planet; it may reduce annual rainfall, especially in
the Americas and northern Eurasia Prof. Peter Saunders
referenced version of this article is posted on ISIS members website
and is otherwise available for download here
Harvard geoengineers are set to spray sun-reflecting
chemical particles into the atmosphere to cool the planet from a balloon at 80
000 feet over Fort Sumner, New Mexico . Chief investigator David Keith
manages a multimillion dollar research fund awarded by Microsoft founder Bill
Gates, and has already commissioned a study by a US aerospace company that made
the case for large-scale deployment of solar radiation management technologies.
The experiment, to be conducted with James Anderson within a year, will release
tens to hundreds of kilograms of particles to measure the impacts on ozone
chemistry and test ways of making sulphate aerosols the appropriate size.
Many scientists are opposed to
geoengineering experiments, preferring to study the impacts of sulphuric dust
emitted by volcanoes, and to use modelling to identify the risks. A British
field test involving a balloon and hose-pipe to pump water into the sky, which
was part of the government-funded Stratospheric Particle Injection for Climate
Engineering (Spice) project (see  Skyhook to Save
the Climate?) was cancelled after public outcry.
But there are
good reasons why geoengineering should not be considered.
Why not to geoengineer
The obvious way to combat climate change is to cool the
planet by reducing emissions of greenhouse gases and removing them from the
atmosphere. That means using less energy, replacing fossil fuels by renewables,
halting deforestation, and adopting sustainable farming practices. As documented in two major reports published by ISIS [3, 4] Food Futures Now: *Organic
*Sustainable *Fossil Fuel Free , Green Energies - 100%
Renewable by 2050, all the necessary technologies
are available and getting better and cheaper every day, only the political will
offers an alternative quick fix, which is to reduce the amount of radiation
reaching Earth’s surface in the first place. There are several suggestions
about how this might be done, for example, by putting mirrors into space or sulphur particles
into the stratosphere, or by increasing the brightness of clouds by spraying sea
salt into them (see  GeoEngineering A Measure
of Desperation, SiS 41). Geoengineering
involves making changes on a planetary scale [5, 6].
A major drawback of
geoengineering, whether it involves solar radiation management (SRM) or other
measures such as fertilizing the oceans in the hope of increasing the
absorption of carbon by phytoplankton, is that it is
likely to be very difficult to reverse. If we sent small particles into the
stratosphere what could happen if they drifted out of position, or coalesced,
or came back down sooner than we anticipated? Not only could the result be a
massive waste of valuable resources, we could end up having done irreparable
harm to the planet.
But if we
could manage to put into the sky something that actually accomplishes what it
was designed to do, i.e., reduce the amount of radiation reaching Earth
by just the amount necessary to compensate for the reduction in outgoing
radiation caused by the greenhouse effect; wouldn’t that solve the problem of
climate change without having to deal with any of the political and economic
obstacles to more conventional measures?
Earth’s climate is a very complex system, and it responds to far more than just
the amount of energy in and energy out averaged over the four seasons and the
entire surface of the planet. The precise spatial and temporal variations in
energy distribution can have very different effects on global climate, and
different SRM measures will lead to different effects. Furthermore, SRM
measures are in no way equivalent to reducing greenhouse gas emissions. And
should SRM measures fail, we are still left with too much greenhouse gases in
It is not hard to see why the
differences should matter. For example, an important factor in driving the
weather is the differences in temperature and pressure between neighbouring
areas. The onshore breezes that are so common in coastal areas in the summer arise
because the air over the land is warmer, and therefore at a lower pressure than
the air over the sea. The temperature differential can also lead to the
formation of clouds near the shore where the two air masses meet. Neither the
breezes nor the clouds would be there if the temperature were the same on the
sea as on the land, even if the mean temperature for the area was the same.
two climate strategies that produced consistently different patterns of heating
and cooling on the surface of the Earth would have different effects on the
climate. What we need to know is whether the differences would be large enough
to matter, and only detailed modelling can tell us that. Work has begun, and
there is a long way to go before we can predict with
confidence what will happen; but it is already becoming clear that SRM would
have serious unintended consequences for the climate.
Earth’s climate is a highly
complex system and consequently very difficult to model. Judgements over which effects
to include and what approximations to make will differ from one research group
to another. That’s why it is important to have several climate models rather
than just one consensus simulation. When the different models make similar
predictions, we can be far more confident of the result. Given the complexity
of the climate and also of the models, it is not at all surprising that the
different models disagree on how much the
temperature will rise as the greenhouse gas concentration increases. On the
other hand, that they all agree Earth will get warmer and - under a reasonably
optimistic estimate of future carbon emissions - by no less than 2 °C, is a
very robust result that we would be very ill advised to ignore.
Comparing the effects of limiting
greenhouse gases on the one hand and reducing the incoming radiation on the
other is even more challenging than modelling the effects of increasing CO2
level. Work has begun and because it is important to be able to compare the
results from different models, much of it is being devoted to a project to find
out how consistent and therefore how trustworthy the different models are .
an international team led by H Schmidt at Max Planck Institute for Meteorology
in Hamburg compared four different climate models, one from the Institute
itself the others from Hadley Centre in the UK, Institut Pierre Simon Laplace
in France, and the Norwegian Meteorological Institute in Oslo respectively .
To start each model, the CO2 level is set to four times what it was
in the preindustrial era, and the solar constant - the amount of radiation reaching
the surface of Earth - adjusted so that Earth’s mean temperature remains what it
was in the preindustrial era. They then ran the models for 50 years.
As you would expect, the mean
temperature averaged over the entire surface of the Earth
remains roughly the same in all the models. On the other hand, the variation in
temperature as we move north or south is reduced from the preindustrial. Given
that, and bearing in mind the importance of temperature gradients in
determining the weather, it is not surprising that the patterns of
precipitation change. Rainfall is reduced on average over the entire planet,
with strong effects over the Americas and northern Eurasia.
The total global cloud cover is also reduced in all the models. This contributes
to the change in albedo (reflectivity) of the planet, which drops by about 2 %
in all four models. The models all predict a stronger effect in Europe
but disagree on what would happen in large parts of the tropics or subtropics.
Note that the reduction in albedo means that less of
the sun’s radiation is reflected from Earth, so more particles or mirrors would
be required to reduce the incoming radiation sufficiently to maintain the
preindustrial mean global temperature.
There are of course many
uncertainties in the calculations. The sudden quadrupling of CO2 is
not realistic, though the rise to four times the preindustrial level is within the bounds of the current climate change models,
albeit at the high end of the range of predictions. On the other hand, holding
the mean global temperature constant is very much a best case scenario, and
secondary effects such as decreased precipitation may well be underestimated.
An Earth with a high level of
greenhouse gases and a geoengineering scheme that compensates by reducing the
amount of incoming solar radiation is not the same as an Earth with
lower level of greenhouse gases and no shield. The mean annual temperature
averaged over the whole planet may be the same, but within that there will be
changes, some quite marked. It is highly likely that total precipitation will
be significantly (and unevenly) reduced, as will the total cloud cover. Beyond
that, it is too early to say what will happen, which is all the more reason for
being very cautious indeed about geoengineering.
It is obvious that if a
geoengineering project goes wrong, the planet could be badly damaged. We are
now discovering that there could be very harmful consequences even if it goes