ENGINEERS ARE looking at ways of reversing global warming, not by lowering the carbon dioxide that causes it but through “geoengineering”, literally changing the face of the Earth to shed heat.
“If we can warm the planet, can we also cool it?” was the title chosen for a session at the AAAS that was marked as much by tensions between the “for” and “against” camps making presentations as by attempts to explain what geoengineering actually involves.
Geoengineering represents attempts to cool the planet by making changes to the Earth’s surface or to the atmosphere or to clouds. A simple example would be to paint black road surfaces white in order to reflect back solar radiation; another is “carbon capture”, taking carbon dioxide directly out of the atmosphere as a way to halt or reverse global warming. The panel was discussing more radical approaches, such as introducing substances into the atmosphere to bring about global cooling.
Dr Ken Caldeira of Stanford University, who was in favour of the geoengineering approach, described some of the ideas being studied. One involved the spraying of sulphur dioxide into the upper atmosphere where it would reflect away solar radiation, in much the same way that the sulphur discharges from a volcano do.
Another approach would see aluminium particles spread into the atmosphere, again to reflect away radiation. None of these techniques are being applied at the moment, however, as researchers attempt to study the long-term implications of tampering with something as fundamental as our atmosphere. “Most of the work going on now is modelling,” Dr Caldeira said.
Prof Martin Bunzl of Rutgers University acknowledged that the use of sulphur might be expected to lower average global temperatures by about 2 degrees but what other effects this approach might cause were unknown.
Nor could you switch off the effect quickly if it was discovered to cause harm. Temperatures would have to be brought back slowly to avoid causing environmental problems. He also dismissed the idea that these techniques could be applied on a small-scale basis, saying: “I don’t believe we can assess the true risk unless we go to a global scale.”
Prof Brad Allenby of Arizona State University was also dismissive of the geoengineering approach. The fractious nature of the panel debate showed “how sketchy our knowledge of geoengineering is”, he said. To pursue these ideas was “extraordinarily naive and extremely dangerous”.
Dr Philip Rasch of Pacific Northwest National Laboratory in Washington state said the ideas should be discussed in “an open dialogue”. He did not advocate immediate use of geoengineering but believed it should be researched so all options were known.
