It's been called the last opportunity the human race has to save the planet. When delegates from nearly 190 nations gather in Copenhagen, Denmark, between Dec. 7 and 18 for the United Nations COP15 conference on climate change, they bring with them the hopes, expectations and fears of billions of people around the world now at risk from irreversible, catastrophic climate change due to rises in greenhouse gas emissions.</PARAGRAPH> <PARAGRAPH>The purpose of the Copenhagen meeting is to forge a successor to the 1997 Kyoto Protocol on greenhouse gas emissions, which expires in 2012. The Copenhagen Protocol, as it will become known, will be the internationally agreed framework for reducing emissions between 2012 and 2020. It is expected to include numerical target reductions for developed countries and at least quantifiable, measurable emissions reductions plans for developing countries, as well as a basic outline for how those targets can be met, financially and technologically.</PARAGRAPH> <PARAGRAPH>The Copenhagen gathering is &#8212; virtually all world leaders, diplomats, scientists, policymakers and environmentalists agree &#8212; the most important conference of its kind since Kyoto. At least 15,000 people are expected at the conference itself, but the city of Copenhagen has suggested up to 100,000 may be present at related events outside the Bella Center conference hall.</PARAGRAPH> <PARAGRAPH>Among the expected attendees are Hollywood and European film stars involved in environmental issues, Nobel laureates including former U.S. Vice President Al Gore, scientists, environmental and development NGOs, anarchists, antiglobalization protesters, industry representatives ranging from traditional oil and gas firms who are strongly against strong targets to renewable energy firms, and green businesses that strongly support them.</PARAGRAPH> <PARAGRAPH>Even those who deny climate change is happening because of mankind's burning of fossil fuels are likely to be roaming the halls of the conference center, trying to persuade negotiators to do nothing.</PARAGRAPH> <PARAGRAPH>The highlight of the conference, though, will no doubt be the gathering of world leaders Dec. 17 to 18 to seal a deal. Nearly 50 world leaders, including Prime Minister Yukio Hatoyama and U.S. President Barack Obama, have indicated they will attend or plan to while others have said they'll go if they are sure a satisfactory deal can be signed. </PARAGRAPH> <PARAGRAPH>Such a gathering of presidents and prime ministers at a U.N. climate change conference is unprecedented and reflects the broad public consensus, and the growing fear, worldwide that time is running out to take action that will prevent severe floods, famines, desertification, rising sea levels, and mass extinctions of plant and animal species due to increased levels of greenhouse gases in the atmosphere.</PARAGRAPH> <SUBHEAD> Broad public consensus</SUBHEAD> <PARAGRAPH> Preparations for Copenhagen began in earnest at a U.N. conference in December 2007. Earlier that year, the Intergovernmental Panel on Climate Change –

, the international group of climate scientists and advisory group to the U.N. whose opinions represent the consensus of the vast majority of the world's leading climate experts, issued a stark warning: Unless the world takes quick action to curb greenhouse gases, especially carbon dioxide, the Earth's average temperature would, over the coming century, increase between 1.5 and 2.5 degrees Celsius compared to the global average temperature between 1980 and 1999.

If that happens, the IPCC said, up to 30 percent of all animal and plant life would face extinction by the end of this century. In addition, an increase in droughts, desertification, severe flooding due to typhoons, rising sea levels due to melting icebergs and disruptive weather patterns worldwide could lead to millions of people becoming "climate refugees," with countries just a few meters above sea level like the Maldives in danger of disappearing underwater completely.

The IPCC offered a number of suggestions to mitigate the most damaging effects of climate change. The scientists suggested that, in order to stabilize CO2 and other greenhouse gas concentrations at 450 parts per million by the end of this century, the highest level where it might still be possible to mitigate the worst effects, according to their climate models, developed countries need to reduce their emissions between 25 percent and 40 percent by 2020, based on their 1990 emission. If the concentration rises above 450 ppm, climate catastrophe is all but certain. Speed is also of the essence, the IPCC added, as world emissions needed to peak by 2015 in order for the concentration level to eventually settle at 450 ppm.

The IPCC did not specifically call on developing nations to announce numerical targets for reduction, though. It has always been the position of countries such as China, India and Brazil that today's climate crisis was caused by developed nations that have been burning coal and oil since the mid-1800s, and that it's their responsibility to take the lead in reducing emissions. The U.N. seemed to agree, but the IPCC did warn that developing nations could not continue "business as usual" when it came to setting reduction goals.