Varun Dutt

Different approaches have been put forward over the years to understand the pros and cons of geoengineering - to deliberately manipulate the earth's climate in response to climate change. In the current scenario however, more research is needed to find the 'perfect' elusive solution.

After several unsuccessful United Nations (UN) negotiation rounds at Copenhagen and Cancun, and the countries not being able to reach an agreement on capping their greenhouse gas emissions, some researchers believe it is time to seriously look into developing a 'plan G' for stopping climate change: geoengineering.
Geoengineering entails the consideration of planet wide engineering projects intended to reduce the side effects of fossil fuel combustion. Rather than trying to stop or reduce emission levels, such engineering projects would: remove carbon dioxide directly from the atmosphere by carbon sequestration through CO2 air capture and ocean iron fertilisation; and, reduce the solar radiation heating the planet by injection of sulfate aerosols into the stratosphere. There are several proposals that fit into the two broad categories although they greatly vary both in terms of their acceptance and the likelihood that they can be feasible on a large scale.
At the first glance, geoengineering solutions hold promising prospects for humanity against climate change. However, scientists scrutinising the geoengineering approach say it could produce dangerous cascading effects, severely disrupting weather and agriculture, and might even fail to block the worst of the greenhouse effects anyway. Moreover, the adverse effects of geoengineering could be worse in south Asian countries like India and China.
Some recent studies published in the special geoengineering issue of Atmospheric Science Letters; April-June 2011, show worrying pitfalls with geoengineering in south Asia. The greatest threat is to the south Asian (Indian) monsoon, which is driven by the temperature difference between warm land and cooler seas. In one geoengineering scheme, it is proposed that a fleet of jets would crisscross the planet releasing around five megatons of sulphur dioxide gas every year. The gas would mix with water in the stratosphere to form minuscule particles called sulfate aerosols, which scatter incoming sunlight back to space before it warms the atmosphere or ground - that is exactly how volcanic eruptions cool the planet. However, according to Alan Robock of Rutgers University, oceans are harder to cool than land. As the sun effectively dims, warmer land cools faster than cooler oceans. Shrinking the land-sea temperature gap would weaken the summer monsoon over Asia and Africa - a possible catastrophe for the billions who depend on the monsoon rain for their crops. In fact, the eight month long eruption of the Laki fissure in Iceland in 1783-1784 (that put large quantities of sulphate particles into the atmosphere) has been known to directly contribute to famine in Africa, India, and Japan, during the same period.
The paper 'The radiative forcing potential of different climate geoengineering options' by T M Lenton and N E Vaughan published in Atmospheric Chemistry and Physics Discussions in 2009, also concludes that the method of injecting sulphate into the atmosphere becomes less effective as the atmosphere becomes more saturated with these particles. Moreover, it is feared that the sulphate injection into the atmosphere could damage the ozone layer as ozone-destroying reactions happen faster on surfaces, such as those provided by sulphate particles, than they do in open air. It is therefore likely that the addition of sulphate to the stratosphere would result in a loss of ozone, and thus result in more ultraviolet radiation getting through. Such ultraviolet radiation is likely to increase the incidence of skin cancer in south Asia as it receives more sunlight. Scientists point out that the eruption of Mount Pinatubo on the Philippine island of Luzon in 1991 led to such a loss of ozone in the area, even as it cooled the climate. The Montreal Protocol banned the use of ozone-depleting substances into the atmosphere and it is expected that the sulphate-based geoengineering option would certainly slow down the Montreal Protocol's ozone recovery and could likely even reverse it.
Furthermore, it is observed that nature already performs a similar sulphate particle trick between the tropics where tropical forests produce a 'blue haze', caused by biological aerosols that enhance condensation of water vapour into mist. A recent study by Renyi Zhanga et.al, titled 'Formation of nanoparticles of blue haze enhanced by anthropogenic pollution' published in Proceedings of the National Academy of Sciences (PNAS) in 2009, reported that industrial sulphur dioxide emissions significantly enhance the production of blue haze by plants. The blue haze in tropics today has however, turned into a smog that makes life unpleasant and hides the sun and the blue sky from view. Geoengineering with sulphates will spread this unpleasantness around the globe.
The problem with 'brown clouds' also provide a cautionary lesson against geoengineering in south Asian countries. Brown clouds are due to the burning of low grade fuels, deforestation, dust, and heavy traffic. They are most prevalent in the rapidly growing, overpopulated regions of the world such as India and China - hence the term 'Asian Brown Cloud', especially around metros like Beijing and New Delhi. The Atmospheric Brown Clouds - Regional Assessment Report with focus on Asia of the United Nations Environment Programme in 2008, suggested that, on the basis of ecosystem modelling, the elimination of atmospheric brown clouds could increase global warming by 0.3° to 2.2°C (and therefore brown clouds could be considered a natural geoengineering solution). Contrary to this is a previous report by J Srinivasan et al., published in 2002 in a paper titled 'Asian Brown Cloud - fact and fantasy' in Current Science that estimated that 2 million people die each year due to respiratory diseases, attributable to the brown cloud. Another report by V Ramanathan, et al. 'Warming trends in Asia amplified by brown cloud solar absorption' published in Nature in 2007, involving direct measurements of the air column within the clouds showed that brown clouds actually increase global warming due to atmospheric heating - so their role as a geoengineering solution is debatable. This difference between modelling and actual measurement should ring alarm bells for those who might consider brown clouds in south Asia as a geoengineering solution. Atmospheric aerosols will certainly kill millions before it stops global warming, if at all.
Further, a study by a group of researchers from Britain's National Oceanography Centre led by R T Pollard, investigated a different idea: dumping iron in the oceans to promote huge blooms of phytoplankton, tiny algae that consume carbon dioxide as they grow. Though much of the carbon thus absorbed returns to the atmosphere when the plankton die, around 8-9 per cent ends up locked away beneath the waves for decades or more. The results of the study appeared in a paper by Pollard, et al., in Nature in 2009. The experiment looked at the effects of iron on the growth of phytoplankton near the Crozet Islands in the southern Indian Ocean. The paper reports that geoengineers have overestimated the amount of carbon removed per ton of iron by between 15 and 50 times. Therefore, iron distribution in the oceans is not a promising geoengineering option as it was thought to be. Moreover, UNESCO's 20-page Report - Ocean Fertilisation: A Scienti?c Summary for Policy Makers 2010, by DWR Wallace, et al., delivers further discouraging news. According to the Report, the effects of tinkering with the ocean's chemistry are largely unknown:
"Large scale fertilisation could have unintended (and difficult to predict) impacts not only locally, e.g., risk of toxic algal blooms, but also far removed in space and time. Impact assessments need to include the possibility of such 'far-field' effects on biological productivity, sub-surface oxygen levels, biogas production and ocean acidification." (http://unesdoc.unesco.org/images/0019/001906/190674e.pdf)
Connected to dumping of iron, in 2007, civil society groups learnt that Ocean Nourishment Corporation (ONC) of Sydney, Australia, a private enterprise, had been given a 'go ahead' by the Philippines government to experimentally dump hundreds of tons of industrially-produced urea, most likely into the Sulu Sea between Philippines and Borneo in south Asia. Because a urea dump could have been dangerous and unacceptable to the marine environment in the area, different civil society groups urged the London Convention (the International Maritime Organisation body that oversees dumping of wastes at sea) to stop ONC from going ahead. The Convention responded favourably and the dumping was immediately aborted.
Few other geoengineering schemes have gained popularity - top of the list being the solar shade, a proposed gigantic umbrella in space that would shield the earth from the sun's rays. This is both the most effective and 'scalable' option, since a hotter earth would simply require a bigger or more opaque parasol. In theory, a solar shade could provide any amount of cooling, but the researchers estimate that it would have to have an area of 4.1 million sq km (half the size of Brazil) to offset half the warming expected over the next century, assuming no cuts in carbon dioxide emissions occur. A polite critic of such a plan might describe it as 'ambitious'.
The consequences or side effects of geoengineering are grave as well. Olivier Boucher of the British Met Office, the UK's national weather service, focused on a plan for ships to spray seawater up above the oceans, where it would evaporate to form a layer of sea-salt aerosols, making marine clouds brighter and reflecting more sunlight back to space. But because of the uncertainty of where clouds would cluster, uniform cooling effect was elusive. In all likelihood it would intensify greenhouse-induced drying in the Amazon, threatening the species that live there, as well as the rainforest's ability to act as a carbon sink.
On a global scale, perhaps, the most worrisome factor is how geoengineering might disrupt 'teleconnections'. These long distance links let atmospheric conditions in one place influence weather half a world away. The best known teleconnection is the El Niño or the Southern Oscillation: warm waters in the eastern Pacific that weaken the easterly trade winds, bringing floods to the Southern US and Peru but drought to Indonesia and Australia.
A study in 2007 by H Damon Matthews and Ken Caldeira, 'Transient climate-carbon simulations of planetary geoengineering', published in PNAS also concluded that the current geoengineering schemes, even under a scenario of increasing emissions, could cool earth within a few decades, to pre Industrial era revolution levels, but that failure of the system would result in a catastrophic, decade long spike in global temperatures with rates of warming 20 times greater than we are experiencing today, as carbon sequestered in plants and soils would be quickly released into the atmosphere. According to Ken Caldeira, "if we become addicted to a planetary sunshade, we could experience a painful withdrawal if our fix was suddenly cut off. This needs to be taken into consideration if we ever think about seriously implementing a geoengineering strategy".
In conclusion, even if safe and effective geoengineering approaches are found, scientists will not know now what the ultimate challenge may be (Table 1). Nevertheless, securing long term political and economic support for such geoengineering measures, especially in countries of south Asia where problems of food, shelter, and poverty loom large, will not be easy. No one would deny the fact that if the world becomes suddenly unwilling or unable to keep supplying say a solar shade even as we continue to pump out carbon dioxide, we will be worse off than where we started.

The author a Post-Doctoral Fellow, Carnegie Mellon University, Pittsburg, USA and Knowledge Editor, Financial Chronicle, New Delhi. vdutt@andrew.cmu.edu