Science in Society Archive

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

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 [1]. 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 [2] 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 I-SIS [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 is missing.

Geoengineering 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 [5] 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?

Unfortunately, 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 our atmosphere.

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.

Thus, 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.

The models

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 [7].

Recently, 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 [8]. 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. 

To conclude

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 right.

Article first published 23/07/12


  1. “US geoengineers to spray sun-reflecting chemicals from balloon”, Martin Lukacs, Guardian, 17 July 2012,
  2. Saunders PT    Skyhook to Save the Climate? Science in Society 52, 44-45, 2011.
  3. Ho MW, Burcher S, Lim LC et a. Food Futures Now, Organic, Sustainable, Fossil Fuel Free, ISIS/TWN, London/Penang, 2008.
  4. Ho MW, Cherry B, Burcher S and Saunders PT. Green Energies, 100% Renewables by 2050, ISIS/TWN, London/Penang, 2009.
  5. Saunders PT and Ho MW. Geoengineering a measure of desperation. Science in Society 41, 2-3, 2009.
  6. Lenton TM and Vaughan NE. The radiative forcing potential of different climate geoengineering options. Atmospheric Chemistry and Physics 9, 5539-61. doi:10.5194/acp-9-5539-2009
  7. Kravitz B, Robock A, Boucher O, Schmidt H, Taylor K, Stenchikov G and Schulz M. The Geoengineering Model Intercomparison Project (GeoMIP). Atmospheric Science Letters 2011, 12, 162-167, doi:10.1002/asl.316.
  8. Schmidt H, Alterskjaer K, Bou Karam D, Boucher O, Jones A, Kristjánsson JE, Niemeier U, Schulz M, Aaheim A, Bendhu F, Lawrence M and Timmreck C. Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO2; climate responses simulated by four earth system models. Earth System Dynamics 2012, 3, 63-78, doi:10.5194/esd-63-2012

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susan rigali Comment left 23rd July 2012 16:04:03
Seems the skies over Los Angeles have been part of this experiment for quite awhile. Many believe the government is spraying "chemtrails" as some sort of population abatement and poison. Somewhat accurate as independent laboratory tests show extremely high levels of barium, copper, manganese, zinc, and aluminum. Barium and aluminum are commonly found in chemtrail fallout. These two compounds were also described by Dr. Teller in his weather modification paper as two possible agents that could be spread by aircraft into the upper atmosphere. His intention was to use them as reflective agents for sunlight in an effort to reduce global heating. "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?" Or if solar reflectors were put into use in thermal components many fields of energy could be produced absorbing the radiant warming effects while reducing reliance on fossil fuels. Agricultural practices, manufacturing, heating and cooling environment, and food production need to be transformed. I contain and employ this process in cooking. The obvious efforts by science has always seemed a battle with nature, through controls. A more relaxed atmosphere where engagement of natural processes could benefit progress and resource availability to many.

Robert Davidson MD, PhD Comment left 23rd July 2012 16:04:53
Geo-engineering is a VERY important topic to humanity. It's taking place without the FULL input of the scientific and medical community. I had heard that aluminum particulates were being placed in the stratosphere. If true, this IMO poses an unacceptable risk of aluminum toxicity to those who might inhale the particles. Aluminum salts are known to cause a strong linear increase in the zeta potential (to more positive values) of our blood. Aluminum salts are known to be neurotoxic. Aluminum salts are likely IMO to lower the agglutination threshold of red blood cells, interfere with the colloidal stability of our blood, and potentiate thrombohemorrhagic phenomena.

Rory Short Comment left 23rd July 2012 18:06:53
The same mindset,which generates the behaviour that is causing our current climate problems, is proposing geo-engineering technologies as a solution to the climate problems but the same thinking that created a problem cannot solve the problem it created, for that a mindset change is needed and that is a tough call.

David Llewellyn Foster Comment left 24th July 2012 07:07:26
As I see it, there is still an enormous cultural reluctance to engage reality as organismic rather than as mechanistic. The problem is not just a cognitive bias, but an inability to use (Blake's) natural imagination, to literally alter our perception and converse "bacterially" for example. Since our formal knowledge of bacterial life is said to be around 2% of its likely potential, it seems to me we are struggling to accommodate procrustean concepts in very limited mental vessels. Time to open it all up in my opinion, to think the unimagined by venturing into realms of pure consciousness, and allowing those realms to inform the symbolic understanding we call science.

Dylan Comment left 25th July 2012 08:08:34
Skybor - the Intended hazards of geoengineering "It is the understanding of the Committee that the following examples are illustrative of phenomena that could be caused by the use of environmental modification techniques as defined in Article II of the Convention: earthquakes, tsunamis; an upset in the ecological balance of a region; changes in weather patterns (clouds, precipitation, cyclones of various types and tornadic storms); changes in climate patterns; changes in ocean currents; changes in the state of the ozone layer; and changes in the state of the ionosphere." Enmod Treaty 1977 Looks like "Solar Radiation management" has been with us at least since the 70`s, coinciding with the onset of "Climate Change". Dare we ask the question - what if they are the same thing? Funny that these chemtrails start getting reported around the same time that global warming sets in and around the same time as the ENMOD treaty is signed in the 70s. If these counterfeit clouds are laid down more predominantly at night, in the winter hemisphere, closer to the poles and microwaved away more predominantly during the day, in the summer hemisphere, towards the equator - global warming will result, even when the sunspot cycle is winding down, unprecendented in history. And .... now they come up with their "solution" to their Solar radiation rigging. Rigged wheels and loaded dice Chemtrails and Weather Derivatives Why in the world are they spraying?

Richard Knowles, B.Sc.(Biol.) Comment left 27th July 2012 14:02:03
Every time we try to fix something, it always leads to more problems. We encourage more studies to create meaningless jobs to solve problems we have both helped create and some that are natural to occur. We do so not to save mother earth but to save our human race from annihilation. Instead, we should allow the earth to balance itself out. It will. It is a self repairing and evolving, algorithmically complex wonder unfathomed by even the greatest human mind. We as humans will suffer for the damage we have created but the earth will shrug us off like a case of bad fleas. We deserve it.

jeeon majumdar Comment left 3rd August 2012 03:03:11
Of course this technology is FKD . The driver here is important: The global freak market. Bill Gates and other major financiers can run amok in the name of Phillanthropy. I am not a Marxist here but as a diagnosis, I believe with the marxists.

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