Climate debate: What's warming us up? Human activity or Mother Nature?

C&EN's cover story notes that global warming believers and skeptics actually agree on a cluster of core points:

• Earth's atmospheric load of carbon dioxide -- the main greenhouse gas -- has increased since the Industrial Revolution began in the late 1700s.
• Carbon dioxide bloat results largely from burning of coal and other fossil fuels.
• Average global temperatures have risen since 1850, with most of the warming occurring since 1970.

"But here is where the cordial agreements stop," writes Stephen K. Ritter, a senior correspondent for C&EN. "At the heart of the global warming debate is whether warming is directly the result of increasing anthropogenic CO₂ levels, or if it is simply part of Earth's natural climatic variation."

Ritter presents a sweeping panorama of global climate change science from the point of view of those who support both scenarios. The story notes that the debate is growing ever more contentious in light of the recent disclosure of e-mail messages suggesting that some scientists supporting the human activities scenario tried to suppress publication of opposing viewpoints.

Most climate scientists maintain that man-made global warming is happening, the article states. This majority opinion has been disseminated in peer-reviewed reports over the past 20 years by the Intergovernmental Panel on Climate Change (IPCC), an entity established by the United Nations and the World Meteorological Organization.

Climatologist Michael Hulme of the University of East Anglia, in England, told Ritter that the scientific evidence backing the basic idea of human activity changing the global climate system is now overwhelming, even if scientific predictions for future climate change are still shrouded in uncertainty.

"It is vital that we understand the many valid reasons for disagreeing about global warming and climate change," Hulme says in the article. "We must recognize that they are rooted in different political, national, organizational, religious, and intellectual cultures -- our different ways of seeing the world.

"But we must not hide behind the dangerously false premise that consensus science leads to consensus politics," Hulme adds. "In the end, politics will always trump science. Making constructive use of the idea of climate change means that we need better politics, not merely better science."

However, global-warming skeptics argue that there is still a lot of guesswork in how scientists come to their conclusions. They take exception to the notion that there is a "consensus" agreement on the science -- that the science is settled and devastating man-made global warming is a foregone conclusion.

"The only contentious aspect of the IPCC assessment is attribution -- what is the cause of global warming and climate change," says atmospheric physicist S. Fred Singer, who is president of the Science & Environmental Policy Project, a public policy institute based in Arlington, Va. "We have looked at every bit of data that IPCC has brought forth, and we see no credible evidence for human-caused global warming. None."

In response to the latest IPCC report, Singer and other scientists formed the Nongovernmental International Panel on Climate Change (NIPCC). NIPCC is an international coalition of scientists -- 35 participants relative to the 2,500 participants in IPCC's 2007 assessment--convened to provide a "second opinion" on the scientific evidence available on the causes and consequences of climate change. The NIPCC report was published by the Heartland Institute, a Chicago-based public policy organization. Unlike the IPCC report, the NIPCC conclusions are not peer-reviewed.