Nature 458, 1077-1078 (30 April 2009) | doi:10.1038/4581077a; Published online 29 April 2009
Without a solid commitment from the world's leaders, innovative ways to combat climate change are likely to come to nothing.
It is not too late yet — but we may be very close. The 500 billion tonnes of carbon that humans have added to the atmosphere lie heavily on the world, and the burden swells by at least 9 billion tonnes a year (see page 1117). If present trends continue, humankind will have emitted a trillion tonnes of carbon into the atmosphere well before 2050, and that could be enough to push the planet into the danger zone. And there is no reason to think that the pressure will stop then. The coal seams and tar sands of the world hold enough carbon for humankind to emit another trillion tonnes — and the apocalyptic scenarios extend from there (see page 1104).
Nations urgently need to cut their output of carbon dioxide. The difficulty of that task is manifest: emissions have continued to rise despite almost two decades of rhetoric, diplomacy and action on the matter. But that unhappy fact should not be taken as a licence for fatalism. Governments have a wide range of pollution-cutting tools at their command, most notably tradable permit regimes, taxes on fuels, regulations on power generation and energy efficiency, and subsidies for renewable energy and improved technologies. These tools can work if applied seriously — so citizens around the world must demand that seriousness from their leaders, both within their individual nations and in the international framework that will be discussed at the United Nations Climate Change Conference in Copenhagen this December.
As essential as it is, however, simply agreeing to cut emissions will not be enough. The fossil fuels burned up so far have already committed the world to a serious amount of climate change, even if carbon emissions were somehow to cease overnight (see page 1091). And given the current economic turmoil, the wherewithal to adapt to these changes is in short supply, especially among the world's poor nations. Adaptation measures will be needed in rich and poor countries alike — but those that have grown wealthy through the past emission of carbon have a moral duty to help those now threatened by that legacy (see page 1102).
Even a complete halt to carbon pollution would not bring the world's temperatures down substantially for several centuries.
The latest scientific research suggests that even a complete halt to carbon pollution would not bring the world's temperatures down substantially for several centuries. If further research reveals that a prolonged period of elevated temperatures would endanger the polar ice sheets, or otherwise destabilize the Earth system, nations may have to contemplate actively removing CO2 from the atmosphere. Indeed, the United Nations Intergovernmental Panel on Climate Change is already developing scenarios for the idea that long-term safety may require sucking up carbon, and various innovators and entrepreneurs are developing technologies that might be able to accomplish that feat (see page 1094). At the moment, those technologies seem ruinously expensive and technically difficult. But if the very steep learning curve can be climbed, then the benefits will be great.
More radical still is the possibility of cooling the planet through some kind of 'geoengineering' that would dim the incoming sunlight (see page 1097). The effects of such approaches are much more worrying than those of capturing carbon from the air, however. The cooling from geoengineering would not exactly balance the warming from greenhouse gases, which would cause complications even if the technology itself was feasible — something for which the evidence has been circumstantial, at best.
But discussions about the possibilities offered by geoengineering could also lull the world's leaders into complacency — if they lead them to believe that the technology will provide an escape hatch if the climate ever does reach a tipping point. This does not mean that the discussions should be avoided, but rather that the speculations need to be backed up with a solid body of research. Moreover, geoengineering research should be framed not as a hope for deus ex machina fixes to sudden global deterioration, but as a palliative cushion for the worst excesses of the peak years that are inevitable even after emissions start to be cut. A world slightly shaded from the Sun while its carbon levels are brought down by means of active capture would be a strangely unnatural place — but not necessarily a bad one, compared with the alternatives.
Research on local and regional interventions to cool Earth should be undertaken now — ideally in a way that provides basic information to climate researchers. Most sciences are in the habit of poking that which they study to gauge its response. Climate researchers lack such a tradition, and might have something to gain by starting one up. The attention to far-off goals, however, must not obscure short-term opportunities. In addition to cutting CO2 emissions, global leaders should curb the release of other substances warming the climate, notably methane and soot, also known as 'black carbon'. Tackling such pollutants will bring other benefits, too, such as reducing the respiratory problems associated with cooking over smoky fires and with high levels of tropospheric ozone.
With so many challenges still to be faced, the climate problem may seem insurmountable. But there is still time left to act, and there is hope to be found in human ingenuity. Humans have a long history of finding new ways to tackle problems, and new ways to circumvent the worst. Without commitment from the highest levels, such ingenuity is likely to come to naught. But with such a commitment, and with a worldwide determination to make a serious cut in emissions, there is much that can usefully, and invigoratingly, be done.
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