Some observers of the climate conference in Paris, and of the preparations leading up to it, sense a greater degree of seriousness and commitment than they saw at earlier international gatherings on climate change. That's encouraging, although it remains to be seen what agreement, if any, will emerge from this conference now that the top leaders have given their speeches and gone home. Another ground for optimism is how, with enough of a stimulant from government in the form of subsidies for clean forms of energy, restrictions on dirty forms of it, and other incentives, market forces can provide momentum to keep going in the right direction. As President Obama noted in his press conference in France, this has already proven to be the case with the dramatic reduction over the last several years in the cost of photovoltaic cells (i.e., solar panels).

There still are plenty of grounds for pessimism about arresting climate change, however, given how apparent and widespread is small-minded thinking that focuses on the parochial and the pecuniary. In addition to any such thinking from abroad to which Mr. Obama was exposed at the conference, he need look no farther than his own capital to be reminded of it. The U.S. House of Representatives chose this moment to pass a resolution that would wreck rules reducing the amount of heat-trapping emissions from coal-fired power plants. It is remarkable that some of the same people who on other topics bemoan what they contend is insufficient exercise of U.S. leadership would do something like this, and that a member of Congress such as Edward Whitfield (R-KY) would say, “Why should this president penalize Americans and put us in jeopardy compared to other countries of the world and require us to do more than other countries are doing, just so he can go to France and claim to be the world leader on climate change?” The House's action also had much the same character as the notorious letter in March from Senate Republicans to Iran about the nuclear negotiations, in that both were designed to scuttle an international agreement by weakening U.S. credibility and bargaining power while the United States was trying to negotiate the accord.

These and other impediments to action mean that the world cannot afford to wait in considering seriously all available means to keep the warming of the planet from reaching levels that would be catastrophic and, within any time frame meaningful for human civilization, irreversible. This in turn means not only minimizing further damage of the environment by reducing greenhouse gas emissions and deforestation but also considering other possible interventions that would counteract the globe-warming effects of the damage already inflicted and that will still be inflicted in the future. This includes measures that come under the heading of geoengineering.

Small scientific communities already have been exploring some of the geoengineering techniques that could be tried. Some would entail accelerated soaking up of carbon on land and in the oceans through the dispersal of appropriate minerals. Other methods would involve reflecting more of the sun's energy outward through seeding of clouds at low altitudes over the oceans or dispersal of sulfur particles at high altitudes (the latter technique mimicking the cooling effect that some major volcanic eruptions have had).

The meager financing and policy attention that have been given so far to geoengineering partly reflects unease over the playing-God aspect of any such effort, an unease that also affects attitudes toward bioengineering. But turning away from any serious consideration of such measures because of the discomfort of having to make what may seem to be God-like choices is itself a choice: a choice not to use an available technology, and a choice that entails costs and risks that might otherwise have been avoided.

A more valid reason for hesitation in turning to geoengineering is that it might detract from the efforts to reduce carbon emissions and to exercise other discipline designed to minimize damage to the natural environment in the first place. Resort to geoengineering might appear to be a giving up on the achievability of damage-limiting goals and could dispel some of the optimism and momentum which President Obama was trying to sustain. But expanded discussion of geoengineering need not and should not be presented as a resort to plan B because we are giving up on plan A. Rather, it is part of addressing an extremely serious threat with all available tools. Even some of the more optimistic scenarios of compliance with emission-reduction goals would not necessarily hold global warming to the oft-cited limit of two degrees centigrade, and even that goal involves an awful lot of damage and degradation of the quality of human lives.

Properly framed, serious discussion of geoengineering might even serve as a spur to the damage-limiting environmental efforts by underscoring the gravity of the situation and clarifying some of the trade-offs involved. If you want to continue using badly polluting forms of energy, then you get that much closer to having to make more of those uncomfortable God-like decisions. Besides, a partially engineered atmosphere in which increased clouds and sulfur particles counteract the effects on temperature of the methane and carbon dioxide is certainly a much less desirable atmosphere to live in and breathe in than an atmosphere that had not been badly damaged in the first place. Another consideration is that some geoengineering measures may be more politically feasible, because of the nature of their economic implications, than some of the principal damage-limiting environmental measures. Even if coal industry interests continue to make the U.S. Congress an impediment to progress, seeding of clouds over the oceans does not have the obvious effect on those interests that rules about power plant emissions do.

There is much to discuss and investigate regarding the technology and financing of geoengineering. At least as important, however, is the political and decision-making side of the subject. Whole new international structures may need to be created before any decisions about particular geoengineering initiatives are made. A fundamental problem is that global warming is a planet-wide disaster in the making with no political authority with sufficient scope and powers to deal with the whole thing. That is why the entire problem of climate change has always had a tragedy-of-the-commons aspect.

Another problem is that different interests get affected differently by climate change, even without getting into geoengineering at all. There are some winners (e.g., increased agricultural opportunities in some cold-climate countries) along with losers, even though humankind as a whole is a big loser. When the objective is limited to minimizing the departure from nature as it was before humans started damaging it, then nature itself provides a standard. The political problem working with such an objective, while hard enough, is not made even harder as it would be by requiring agreement on objectives that are more the artifice of humans than just limiting destruction of nature by humans. With geoengineering, however, although the intention would be to mimic nature with regard to a particular dimension such as average global temperature, the rest really is manmade stuff. Points of convergence on which to reach an international consensus on what ought to be done would be all the harder to find. The local effects of some possible geoengineering efforts also might engage different local interests differently. For example, cloud-seeding in parts of the ocean that would be best suited for use of that technique might have some undesirable weather effects on nearby land areas.

Difficult problems indeed—all the more reason to start talking about them seriously sooner rather than later.