GLOBAL WARMING

Global warming has become perhaps the most complicated issue facing world leaders. On the one hand, warnings from the scientific community are becoming louder, as an increasing body of science points to rising dangers from the ongoing buildup of human-related greenhouse gases — produced mainly by the burning of fossil fuels and forests. On the other, the technological, economic and political issues that have to be resolved before a concerted worldwide effort to reduce emissions can begin have gotten no simpler, particularly in the face of a global economic slowdown.

World leaders gathered in Copenhagen in December 2009 for a session tha that had been years in the making but that fell short of even the lowered expectations with which it opened. The 192 nations in attendance at the end merely agreed to try to reach a binding accord before at a follow up meeting in Cancun, Mexico, in December 2010. By the summer, Ban-Ki Moon, the United Nations Secretary General, was saying that no sweeping accord was likely, and recommending that a better approach might consist of small steps in separate fields that built toward wider consensus.

At the heart of the international debate is a momentous tussle between rich and poor countries over who steps up first and who pays most for changed energy menus.

In the United States, Democratic leaders in the Senate in July 2010 gave up on reaching even a scaled-down climate bill, in the face of opposition from Republicans and some energy-state Democrats. The House had passed a broad cap-and-trade bill in 2009.

In the meantime, recent fluctuations in temperature have intensified the public debate over how urgently to respond. A string of large snowstorms in the Washington area and freezing weather in Florida in the winter of 2009-2010 were seized on by climate change skeptics. But the combination of flooding, heat waves and droughts in the summer were taken by most researchers trained in climate analysis as evidence to show that weather extremes are getting worse.

The long-term warming trend over the last century has been well-established, and scientists immersed in studying the climate are projecting substantial disruption in water supplies, agriculture, ecosystems and coastal communities. Passionate activists at both ends of the discourse are pushing ever harder for or against rapid action, while polls show the public locked durably in three camps — with roughly a fifth of American voters eager for action, a similar proportion aggressively rejecting projections of catastrophe and most people tuned out or confused.

http://topics.nytimes.com/top/news/science/topics/globalwarming/index.html