Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Geoengineering schemes under scrutiny

Researchers divided over the wisdom of climate manipulation.

The cooling aerosols pumped into the atmosphere by the 1991 eruption of Mount Pinatubo inspire one proposed approach to fight global warming. Credit: NASA

Geoengineering — the deliberate manipulation of climate to counteract global warming — might not be taking off just yet, but the push to fund more research into it is increasing.

This week, Novim, a think tank based in Santa Barbara, California, released a report that investigated the feasibility of one of the wilder-sounding geoengineering schemes: pumping tiny particles into the upper atmosphere to block sunlight and trigger global cooling.

"It's the most serious technical report to date," says David Keith of the University of Calgary in Alberta, Canada, who has been researching geoengineering for two decades. Keith was an author on the report, which was led by Steve Koonin, now chief scientist for the US Department of Energy, and Jason Blackstock of the International Institute for Applied Systems Analysis in Laxenburg, Austria.

It's the most serious technical report to date. David Keith

Among other things, it concludes that spraying sulphate aerosols — to mimic the cooling effects of a major volcanic eruption — is technically feasible. But the political and ethical challenges facing such a worldwide intervention remain virtually unknown, as do its unintentional side effects.

Those potential side effects could include irrevocably altering precipitation patterns, argue Gabriele Hegerl, of the Grant Institute in Edinburgh, UK, and Susan Solomon, of the US National Oceanic and Atmospheric Administration in Boulder, Colorado, in a paper published online on 6 August in Science1.

They cite the instance of the 1991 eruption of Mount Pinatubo on Luzon island in the Philippines, which injected sulphur particles high into the stratosphere, causing global precipitation and river flow to drop dramatically. "Geoengineering schemes optimized to cancel greenhouse warming will lead to a less intense global hydrological cycle and major regional changes," agrees Philip Duffy, a researcher at Climate Central in Palo Alto, California.

Outlandish schemes

Duffy and Keith both spoke in Albuquerque, New Mexico, at the annual conference of the Ecological Society of America. They participated in a symposium on 6 August that aimed to make ecologists more aware of the field, which, until now, has mainly been dominated by experts in climate, the atmosphere or the ocean.

Geoengineering schemes are often notable for their sheer outlandishness. The sulphate scheme studied in the Novim report would require giant hoses or cannons to constantly blast particles into the air. Other plans call for installing tens of thousands of reflective sunshades in orbit to block incoming sunlight, or for seeding vast swathes of the ocean with iron in an effort to trigger plankton blooms that would suck down carbon dioxide from the atmosphere.

Keith notes that both the public and researchers often confuse the two main approaches to geoengineering: solar radiation management, which aims to block incoming light using techniques such as aerosols or sunshades, and carbon cycle engineering, which uses techniques such as ocean fertilization. Solar management is relatively cheap and fast, but comes with unknown effects on the climate system; engineering of the carbon cycle is slow and expensive "but gets the carbon out", he says.

Humble beginnings?

Keith and the other authors of the Novim report argue that research should begin into the effects of small-scale geoengineering experiments. "You don't have to do it on a large scale," he says. The report recommends, for instance, preliminary work on determining the best way to deliver and disperse sulphur aerosols, and on wind-field and other modelling to work out how the particles might spread throughout the stratosphere. It also lays out what sort of field tests might be needed to validate this work, including "a non-trivial stratospheric aerosol loading to be maintained for several years".

It does not put numbers on the cost of such research, nor does it identify which country should take the lead on it. It calls for "international processes" to be put in place to develop guidelines for coordinating potential responses from various countries.

In another report issued today, the Copenhagen Consensus Center — a Denmark-based group founded by Bjørn Lomborg, author of the book The Skeptical Environmentalist — tackles the potential costs of several geoengineering schemes. It argues for spending US$750 million every year for the next decade on geoengineering research, particularly on solar radiation management and the study of its side effects.

Meanwhile, the UK Royal Society is expected to release a detailed report on geoengineering options in September, the first major scientific academy to do so.


  1. Hegerl, G. C. and Solomon, S. Science advance online publication doi:10.1126/science.1178530 (2009).

Download references


Related links

Related links

Related links in Nature Research

Nature Reports Climate Change

Related external links

The Novim report on climate engineering

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Witze, A. Geoengineering schemes under scrutiny. Nature (2009).

Download citation

  • Published:

  • DOI:


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing