But large developing countries can and should be expected to act, too. At the 2009 Copenhagen climate conference, China agreed to moderate but serious reductions in its economy's carbon intensity how much carbon dioxide it produces for every unit of gross domestic product a result possible only because President Barack Obama brought a carbon-cutting pledge to the table. If countries merely sustain their Copenhagen commitments, that alone will bend the global emissions curve down, a 2013 MIT analysis found.
Since Copenhagen, China has offered a mixed picture, not confirmation that it will do nothing. The country has built coal-fired plants, but its rulers are also investing in nuclear power, experimenting with carbon pricing and emphasizing environmental considerations with increasing urgency. The government has little choice; air quality in the north has become a noxious social problem, and China faces a variety of climate risks.
Next year, international negotiators will meet in Paris. They will bring their national contributions, already vetted at home, to the conference and bundle them together. This system may not drive down emissions as quickly as the top-down treaty of activists' dreams. But it is achievable, and the pledges will be more reliable.
Experts at MIT and elsewhere anticipate that some countries, such as India and South Africa, will bring little to the table but that China will expand on its previous commitments. Added to others' pledges, backed by efforts already underway, this would move the global emissions curve down more, heading off catastrophic high-emissions scenarios. Even so, the emissions trajectory would still be above the path scientists recommend to keep global temperature rise moderate. In other words, sustained, contentious diplomatic effort will be required after Paris. The United States must be a driver; no country has pumped more greenhouse gas into the atmosphere, and no global effort will succeed without U.S. buy-in and leadership.
In trade agreements, other environmental accords and arms-reduction pacts, countries have shown they can overcome mutual suspicion when cooperation offers clear, long-term benefits. A U.S. commitment would offer other countries confidence that the United States will jump with them and allow U.S. diplomats to isolate laggards. Congress can help: Putting a price on U.S. carbon emissions, and applying a charge on imports from countries without a strong anti-emissions policy, would give China and others an incentive to implement plans of their own.
The world will not give up fossil fuels tomorrow or many years from tomorrow. The transition scientists recommend will be slow, and the world may have to adapt to risks it did not have enough sense to avoid. But pointing out the difficulty of the problem is not a strategy. It is an excuse to shrink from one of history's greatest challenges.