About 15,000 delegates, environmentalists, scientists, journalists and others gathered in Copenhagen on Monday to begin two weeks of negotiations on what to do about climate change.
Why is this meeting happening?
It's called "COP-15" for the 15th Conference of Parties to the 1992 U.N. Framework Convention on Climate Change. The 1992 deal is better known as the Rio treaty. That agreement was ratified by 192 nations, including the United States. Since then, delegations have met each year to discuss how the world can combat global warming.
The most important previous meeting was in Kyoto, Japan, in 1997 when a treaty protocol ordered cuts in carbon dioxide and other global warming gases by 37 industrialized nations. The United States rejected that pact.
But neither the agreements in Rio de Janeiro nor Kyoto curb greenhouse gas emissions enough to meet scientists' goals.
What's expected to be accomplished at this summit?
The first week of the conference will focus on refining the complex text of a draft treaty. But major decisions will await the arrival next week of environment ministers and the heads of state in the final days of the conference, which ends Dec. 18.
Copenhagen is expected, at best, to reach political agreements by industrial nations to cap emissions by 2020, to be followed by a binding treaty next year. Developing nations also are expected to rein in fossil fuel use and slow growth in emissions.
Another important element involves rich nations paying poor ones to help them deal with droughts, floods and other effects of climate change, and to install clean-energy technology to curb their own emissions.
According to the BBC, another goal is a carbon trading scheme aimed at ending the destruction of the world's forests by 2030.
What would such an international agreement achieve?
A study released Sunday by the U.S. Environmental Protection Agency said the emissions reductions pledged in recent days would fall far short of what's needed to keep temperatures from rising to dangerous levels. That benchmark is anything more than 3.6 degrees (2 degrees Celsius) above temperatures before the Industrial Revolution, when widespread use of coal and other fossil fuels began.
If that is to be met, scientists say that developed countries will need to cut their greenhouse gas emissions by 25 to 40 percent by 2020 and by 80 to 95 percent by 2050. Developed countries must substantially reduce the growth rate in their emissions.
What happened Monday?
On the sidelines, climate activists competed for attention on deforestation, clean energy and low-carbon growth. Activists plan to hold protests in Copenhagen and around the world on Dec. 12 to demand that delegates act.
The BBC reported that small island states want a lower target for warming, 1.5 C (2.7 F), to lessen the impact from rising sea levels. Some African nations, and even China, may support this.
What about the United States?
President Obama will attend the end of the conference, which is taken as a signal that an agreement was getting closer. The House passed climate legislation this summer, but the bill has been delayed in the Senate.