An article written by Professor Andy Ridgwell, Professor Chris Freeman and Professor Richard Lampitt.

The idea of deliberately manipulating the climate of a planet is a familiar theme in science fiction. Known as ‘terraforming’, cold planets, such as Mars or even the Moon, would be warmed by the addition of atmospheric greenhouse gases, while excessively hot planets such as Venus would be cooled by reducing the strength of solar radiation via space-based “sunshades”. Increasing concern about the potentially very serious consequences of global warming on our own planet has led to an explosion of interest in whether Earth’s climate could be deliberately modified to counteract global warming and climate change, a process known as “geoengineering”.  In September 2009, the Royal Society published its seminal report Geoengineering the climate: science, governance and uncertainty, describing this emerging field. 

Professor John Shepherd FRS explains geoengineering (3 mins, requires Flash Player).

The history of geoengineering actually pre-dates much of the science fiction literature on terraforming. The Swedish scientist Svante Arrhenius ForMemRS (1859–1927), who first recognised the important link between carbon dioxide (CO2) and the ‘greenhouse effect’, considered the climatic implications of industrial activities and the burning of coal. He wondered whether coal burning should be increased in order to enhance greenhouse warming, considering it beneficial because of the harsh Swedish winters.

    Professor Stephen Salter on spraying sea water to make clouds whiter
    (3 mins).
  • Listen here.

However, the first serious consideration of geoengineering was not until the 1960s and 70s when, at the height of the Cold War, the former USSR considered ways to warm its vast, icy tundra in the hope of generating fertile farm land. Today, the feasibility and desirability of geoengineering are being seriously assessed by researchers and governments as a means of altering the Earth’s climate system to ameliorate the global warming impacts of continuing CO2 emissions.

Flettner cloud seeding vessel with turbines (credit: John MacNeil).

Geoengineering encapsulates a multitude of schemes and ideas; some practical and costed, some almost pure science fiction. All are aimed at reducing global warming and adopt one of two basic lines of approach to the climate system:  removing CO2 from the air and thus restricting the intensity of the greenhouse effect, or directly reducing the amount of solar energy absorbed by the Earth (“solar radiation management” or SRM). The scales and magnitude of impact of the different interventions range from a complete reversal of recent surface warming globally and the capture of all fossil fuel CO2 released to date, down to a reduction in the severity of heat waves and drought in specific regions. As geoengineering is increasingly brought into the national and international debate, the distinctions between the two different approaches and the scale of intervention may become critical. Carbon capture deals with the root of the problem: the ‘excess’ CO2 present in the atmosphere. SRM schemes might cool the planet but are only addressing the symptoms, not the underlying cause. In addressing only the greenhouse gas induced warming, the geochemical consequences of CO2 released into the atmosphere then dissolving into ocean surface waters - “ocean acidification” - would continue unabated and the current diversity and economic value of marine ecosystems and resources may be damaged. Global radiation balancing schemes should thus arguably only be used should a rapid “emergency” response to rising temperatures be required. In contrast, small scale and regional deployments of SRM schemes (through, for example the incremental deployment approach described by Lee Lane of the US House Committee on Science & Technology (2009)) may find a natural place in a mix of efforts to mitigate climate changes because the costs are generally much lower. 

    Dr James Lovelock FRS on the Royal Society report on geoengineering
    (2 mins).
  • Listen here.

Clearly, the impacts, benefits, uncertainties and costs of proposed schemes must be weighed and assessed. There may be unexpected negative side effects of many or all of the proposed schemes, and a great deal more research on their effectiveness and impacts, as well as full assessment of the technologies required, is needed before any decision can be taken. While we are already progressively modifying our climate system by releasing vast amounts of CO2 to the atmosphere, the decision to directly intervene in the climate system and implement some form of large-scale geoengineering cannot be taken lightly, as it is intimately bound up with the welfare of future generations and the stability of ecosystems. Short term gain in reduced surface temperatures may result in higher CO2 in the long term or centuries-long commitments to expensive geoengineering procedures. 

Satellite image of phytoplankton bloom occurring from the Southern Ocean Iron Enrichment Experiment (SOIREE). The arced distribution is due to oceanic currents. (image: NASA).

It is essential to reduce emissions as quickly as possible in order to create the most room for manoeuvre. If geoengineering is deemed necessary, the negative consequences and risks will be much smaller if less CO2 is to be countered. It cannot be overemphasised that geoengineering must never be relied upon to stop global warming. For that, emissions cuts remain key. However it would be foolhardy not to formulate our “Plan B”, and to advance geoengineering science and technology to create that option, should policy makers fail to grasp the urgency of the problem and emergency action be required in decades to come.

Banner image: Sources and sinks of atmospheric carbon dioxide across Earth, measured in 2003 (credit: NASA)

Discussion meeting

This article is based on the discussion meeting 'Geoengineering – taking control of the planets climate' which was held on 8-9 November 2010.

Related policy report

Geoengineering the climate: science, governance and uncertainty

Published September 2009.

From the Royal Society's archives

Meteorological record keeping was a staple, but passive, activity of 17th and 18th century gentlemen and extreme weather conditions were always worthy of discussion and publication. Interest increased in 1859 due to the wreck of the passenger vessel Royal Charter, which left 450 people dead off the coast of Anglesey after a hurricane force gale. As his former ship-mate was publishing On the origin of species, HMS Beagle´s erstwhile commander Captain Robert Fitzroy (then leader of the British Government´s statistical office for meteorology) started producing weather forecasts: the first appeared in 1860, but they were routinely wrong. However, he established the Meteorological Office as a scientific body of real merit.

John Evelyn FRS’s 1661 book Fumifugium: or, the inconvenience of the aer, and smoke of London dissipated...1contended that air pollution made London resemble Mount Etna and correctly identified the cause as "that Hellish and dismall Cloud of SEA-COALE". Evelyn´s suggested solution was to move industrial activity five or six miles out of London, but his book was ahead of its time and when presented to King Charles II it made only a minor impression. The idea that human beings might have an impact on the atmosphere of the entire globe only began to be recognised in the late 19th century - Svante Arrhenius ForMemRS discussed the idea in his book Worlds in the making2.

However, it has been only in the past few decades, with the advent of powerful computers for simulating ideas about how the climate system and carbon cycle works and might be modified, that the notion of deliberately taking control of climate and geoengineering entered the scientific (and increasingly political) arena. David Keith said in his recent paper Engineering the planet: "I judge it likely that this century will see serious debate about - and perhaps implementation of – deliberate planetary-scale engineering."3

[1] J. Evelyn (1772), Fumifugium: or, The inconvenience of the aer, and smoake of London dissipated, together with some remedies humbly proposed, Published for B.White , London, (New ed., i.e. 1st ed reprinted)

[2] S. Arrhenius (1906), Världarnas utveckling published as Worlds in the making: the evolution of the Universe, by Svante Arrhenius; translated (from the Swedish) by H. Borns, Harper, London, 1908

[3] D. W. Keith (2010). Engineering the Planet, Chapter 49 in Climate Change Science and Policy edited by S. Schneider and M. Mastrandrea, Island Press, Washington DC, 2010