2014年经济学人 气候变化与地质工程学 地球发光令人担心（在线收听）

Climate change and geoengineering

Fears of a bright planet

Experiments designed to learn more about ways of geoengineering the climate should be allowed to proceed

SHINY things absorb less heat when left in the sun. This means that if the Earth could be made a little shinier it would be less susceptible to global warming. Ways to brighten it, such as adding nanoscale specks of salt to low clouds, making them whiter, or putting a thin haze of particles into the stratosphere, are the province of “geoengineering”. The small band of scientists which have been studying this subject over the past decade or so have mostly been using computer models. Some of them are now proposing outdoor experiments—using seawater-fed sprayers to churn out particles of the exact size needed to brighten clouds, or spewing sulphur particles from underneath a large balloon 20km up in the sky.

The aims are modest. The scientists hope to understand some of the processes on which these technologies depend, as a way of both gauging their feasibility (can you reliably make tiny puffs of sea salt brighten clouds?) and assessing their risks (how much damage to the ozone layer might a stratospheric haze do, and how might such damage be minimized?). The experiments would be far too small to have any climatic effects. The amount of sulphur put into the stratosphere by the experimental balloon would be 2% of what a passenger jet crossing the Atlantic emits in an hour.

Nonetheless, these experiments—and this whole line of research—are hugely controversial. Many scientists are skeptical about geoengineering and most greens are outraged. Opponents object to them for a range of reasons. Some are against the very idea of geoengineering and any experiments in the area, even those which pose no immediate risk to the environment. They abhor the hubris involved in trying to affect the mechanics of the climate and despair at the potential diversion of attention from controlling carbon emissions as the route to countering climate change. They find the idea of some–possibly many—countries having the power to change the climate for the whole planet a geopolitical nightmare. Even modest experiments in geoengineering, according to this logic, are the beginnings of a slippery slope, one that will engender a false sense of security and domesticate an idea that should have always remained outrageous.

Yet caving in to this opposition would raise, rather than reduce, the dangers to the planet. Geoengineering is not an alternative to mitigating climate change by cutting carbon emissions, but it may be needed as a complement to it. Although pressure for cuts in carbon emissions through negotiations such as those currently taking place in Lima is yielding results—witness the recent agreement by China and America on new reduction targets—it has so far been insufficient to the task, and emissions look set to rise for decades yet.

Even if emissions do eventually start to fall, the cuts will take decades to have any effect so temperatures are likely to go on going up for some time. Although they have not soared in the past couple of decades as they did in the 1980s and 1990s, there is a fair chance that this year will tie with the hottest on record. The planet is not getting cooler and the pressures on the climate are unlikely to go away. It is therefore not too hard to imagine a world, decades hence, in which emissions are falling but temperatures are rising steeply and the ability to adapt to them has been stretched too far. An additional way to stabilize temperatures might then seem in order. Geoengineering offers that possibility.

Knowledge can be dangerous; ignorance can be worse

Research on a question of such gravity will have implications beyond its scientific results. But that is a reason to hold the scientists to high standards, not to duck the experiment entirely. If the research consists of safe, well-conceived experiments designed to improve scientific understanding of the processes involved; if it is conducted by people who openly discuss with the public the implications of their research; if it is funded by bodies that take the need for transparency and debate about the risks inherent in such research seriously: then it deserves to be approved.

There are all sorts of reasons why geoengineering may prove impossible, either politically or scientifically. It may be too dangerous to countenance, and the circumstances which might make it an appealing complement to cutting emissions may never arise. But to treat research into the subject as taboo on the basis that ignorance is a viable defense against folly would be a dangerous mistake.