Grand words and pledges flowed out of the United Nations climate change summit in New York this week, as they always do when the world pauses to remember the dangers of melting glaciers and rising seas. This time, businesses — including a few oil companies — joined U.S. President Barack Obama and other world leaders in vowing to rein in climate-warming emissions. Yet, as the Washington Post's Wonkblog put it, "What good is a climate summit without emissions cuts?"

Still, the dignitaries departing New York should not be too down on themselves: They face a virtually impossible task. Reaching an international agreement on any environmental topic (much less the ridiculously complicated issue of climate change) has rarely happened over the last 15 years. Such agreements, which in the past have helped fix the ozone hole above Antarctica and ban nuclear weapons testing in the air and sea, are now themselves a kind of endangered species, partly because once-robust American leadership on this front has faltered.

Using a University of Oregon database, I ran a search to see how the number of environmental agreements has changed over time. Looking just at multilateral deals, I found that the number of agreements (including, commonly, amendments that revise prior agreements) spiked in the 1990s and then dropped off in the 21st century. To be specific: There were 107 agreements in the 1960s; then 143 in the 1970s; 175 in the '80s; 353 in the '90s; 244 in 2000s; and 70 so far in the 2010s (the final entry on the multilateral database, the Minamata Convention on Mercury, is from late 2013).

The 1992 Earth Summit in Rio de Janeiro, attended by U.S. President George H.W. Bush, probably marked the high point for international environmental action, says John Knox, a professor of international law at Wake Forest University. Major agreements came swiftly, many of them produced out of the Rio summit itself: the 1992 U.N. Framework Convention on Climate Change; the Rio Declaration on Environment and Development; Agenda 21, a nonbinding 1992 sustainable development plan; and the 1992 Convention on Biological Diversity. The long-term success of these agreements is certainly debatable, but they did lay the groundwork for modern efforts to combat climate change and protect wildlife on land and in the sea. The 1992 climate convention, for example, sought to stabilize greenhouse gas emissions at levels below the danger zone, and the 1997 Kyoto Protocol followed on with countries' specific emissions-reductions targets. It was an optimistic time, notes Jutta Brunnée, a professor and the interim dean at the University of Toronto's Faculty of Law who specializes in international law. The Berlin Wall had just fallen, and momentum for a new world order seemed to reign. In retrospect, she says, the Rio climate agreement seems like a "miracle" that could not be reproduced today.

By the time Kyoto hit in 1997, the downslide was beginning. Since the 2001 Stockholm Convention on Persistent Organic Pollutants, only one major environmental agreement has been drafted: 2013's Minamata Convention on Mercury, an effort to contain mercury mining and pollution from sources like dental fillings. It has yet to be ratified. (Plenty of minor agreements have been drafted too, like the "Agreement on the Central Asian and Caucasus Regional Fisheries and Aquaculture Commission" or the "Agreement on the Nile River Basin Cooperative Framework.") But the effort to curb climate-warming emissions, which come from every industry and every nation and relate to several types of pollutants (carbon dioxide, methane, refrigerants, and so on), will be vastly more complex than any other agreement. "It's staggering what needs to happen to get a grip on climate change," says Brunnée. "It's not as easy as eliminating one chemical."

To be fair, Knox and Brunnée say that some of the low-hanging fruit in terms of environmental agreements has been plucked, like efforts to plug the ozone hole, minimize nuclear testing, and combat pollutants like mercury. All of those are ongoing efforts, requiring international negotiators to come together to approve amendments that may adjust or tighten prior requirements.

But it is also true that American leadership has waned. The United States was a pivotal force in prior agreements, such as those reducing ozone (the Montreal Protocol) or banning nuclear weapons tests. Now, notes Knox, the U.S. Senate cannot even muster the will to ratify even popular treaties such as the Law of the Sea, which is backed by groups as diverse as environmentalists and the Pentagon. (It establishes standards for deep-sea mining and fishing and clarifies countries' rights in ocean waters near land.) The holdup for the most part does not lie in the executive branch — President George W. Bush backed the Law of the Sea treaty, for example, and in vain asked the Senate for ratification of more obscure treaties such as the Agreement on the Conservation of Albatrosses and Petrels and the International Treaty on Plant Genetic Resources for Food and Agriculture. It is the Senate that is paralyzed.

With the United States clearly divided and ambivalent about joining international environmental agreements, the energy and enthusiasm in the rest of the world for those agreements wane. It even seems likely that wildly successful agreements of the past would be held up should they encounter today's partisan divide. The Montreal Protocol, a 1987 agreement that is helping phase out substances that had dangerously depleted the protective ozone layer high in the stratosphere, is regarded as a huge success. But were it to have been negotiated today, the Senate roadblock would likely loom. "It's certainly hard to see how even something as obviously in the U.S. self-interest as the Montreal Protocol could get through," Knox of Wake Forest says.

It's not just the environment. International agreements in general have had a rougher time over the past 20 years. No major international trade agreement has passed since the 1990s, notes Knox. Climate change is another 20-year effort that remains far, far from complete. These holdups may reflect the realities of a world growing up, from unipolar to multipolar, with countries less eager to fall into line, especially as they increasingly understand the importance and ramifications of these agreements. But environmental issues have unquestionably become a political and economic lightning rod, with the international difficulties simply reflecting domestic American realities.

Forty years ago, before the free market conservative movement that culminated in the Tea Party truly dug in, environmentalism enjoyed its political heyday. President Richard Nixon, a Republican, created the Environmental Protection Agency and signed the Endangered Species Act and the Clean Air Act, two landmark environmental laws whose influence remains strong to this day. Four decades later, Republicans seek to repeal or weaken such laws as the party has shifted rightward. The most recent major U.S. environmental legislation, says Knox, was the 1990 Clean Air Act amendments — nearly a quarter-century ago. Back then, George H.W. Bush was president, Newt Gingrich and his Contract with America were still four years in the future, and acid rain was on everyone's mind when both the Senate and the House overwhelmingly passed the legislation, with bipartisan support. Internationally, says Brunnée, environmental issues may also be harder to work through than other issues, like human rights, because of the economic impact they carry. They are also tripped up by doubters: Whereas no one can dispute streams of refugees, plenty of people like to question climate science. That has prompted plenty of American lawmakers, and some might argue the entire nation of Australia, to back away from the idea of cap-and-trade or a carbon tax as industry interests win out.

None of this history bodes well for the climate. Obama seems committed and is vowing to slash emissions through executive actions. But even if fixing climate change were relatively simple — a flat carbon tax all-around! — both American and global politics would make it much tougher to push through than 20 years ago. Where before the world looked to American leadership for the landmark environmental agreements of the past, today it sees mostly bitter partisanship and disagreement. Long-term, collaborative thinking is not in vogue. Congress will never pass cap-and-trade, at least until Miami starts flooding. And other big polluters, like China and India, will not lightly sign onto an international accord that could upend their economies, at least in the near term. The giddy optimism of the Rio days has given way to a long, almost paralyzing slog.

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