A leaked draft of the report points out that the link between fossil-fuel burning and climate change is already observable: "It is extremely likely that human influence on climate caused more than half of the observed increase in global average surface temperature from 1951 to 2010. There is high confidence that this has warmed the ocean, melted snow and ice, raised global mean sea level and changed some climate extremes in the second half of the 20th century." If you look beyond the tables and charts and graphs that fill the reports, you can see the Arctic vanishing, great cities like Miami and Shanghai drowning, droughts causing famine in Africa, and millions of refugees fleeing climate-related catastrophes. Rajendra Pachauri, the head of the IPCC, recently told a group of climate scientists that if we want to avoid this fate, governments must act now to cut carbon pollution: "We have five minutes before midnight."
"For a lot of scientists, ClimateGate was a real awakening," says Naomi Oreskes, a science historian at Harvard and co-author of Merchants of Doubt, which chronicles the fossil-fuel industry's long battle to undermine climate science. "It was clear that if you were going to work on climate change, you were a public figure. And it was no longer enough to just do the science. You also had to go out and explain it to people – and defend it." By then, Santer reports, he was receiving countless death threats. "Most of the world does not have a problem with denial of climate change," says Anthony Leiserowitz, director of the Yale Project on Climate Change Communication. "It's only an issue in Australia, Canada and, most significantly, the United States." Although the U.S. population as a whole is moving toward accepting the reality of climate change, Congress remains a scientific backwater. One recent analysis by the Center for American Progress found that almost a third of the 535 members of the House and Senate are climate deniers. Not coincidentally, those 161 reps have taken more than $54 million in political contributions from the fossil-fuel industry.
The second issue that has come up is the question of a "hiatus," or pause in surface-temperature warming. Texas Sen. Ted Cruz, winner of a climate-denier award from Texas green groups, recently proclaimed that "there has been no recorded warming since 1998." Not exactly, Ted. According to the IPCC draft report, the rate of warming at the planet's surface is lower over the past 15 years, but warming has not stopped. In fact, since the 1950s, each successive decade has been hotter than the last, and the 2000s were the hottest decade since modern record-keeping began in 1880. Scientists have a variety of explanations for this, including the fact that more heat is being transferred deeper into the ocean and that volcanic eruptions have blocked sunlight. "We never expected warming to be linear," says Kevin Trenberth, senior scientist at the Climate Analysis Section at the National Center for Atmospheric Research in Boulder, Colorado.
The past few years have seen an expansion of Antarctica's coastal ice sheets – a byproduct, ironically, of climate change, which has brought increased snow and rainfall to the continent. Meanwhile, Antarctica's inland ice sheets are melting at an alarming rate – 1,350 billion tons of ice disappeared into the ocean between 1992 and 2011. And that rate is increasing, fueling global rises in sea level.
Many skeptics claim that ice ages have come and gone over the millennia, and global warming is no different. But those earlier climate shifts were caused by phenomena like changes in the Earth's orbit. The current rise in global temperatures has coincided with a nearly 40 percent rise in CO2 levels over the past 150 years.
True, perhaps, for rich countries. But the worst impacts of climate change – drought, famine, disease – will disproportionately strike the poorest nations. And even the well-off will be hit hard: Between 2011 and 2012, the U.S. government dished out more than $100 billion in climate-related emergency spending.
This may be true for the Earth's surface, but, according to NASA's Josh Willis, it doesn't tell the whole story, because "over 90 percent of the heat trapped by global warming is going into the oceans."