Telling Americans that scientists don't agree is the classic climate denial strategy. It's been over a decade since consultant Frank Luntz famously furnished the GOP with strategies to kill climate action during the Bush years, recommending in a leaked memo [PDF]: "you need to continue to make the lack of scientific certainty a primary issue." Oh, yeah, and avoid truth: "A compelling story, even if factually inaccurate, can be more emotionally compelling than a dry recitation of the truth." It seems to have worked: Only a minority of Americans believes global warming is caused by humans: 42 percent, according to a 2012 Pew study.

A carbon tax of $25 per ton of emissions would cut the deficit by $1 trillion over a decade, according to the Congressional Budget Office (CBO).

At an average global temperature rise of 4C, the hottest days experienced would be 6C to 12C hotter, sea levels would rise by 80 cm or higher and the yields for key crops such as maize, wheat and rice would drop by as much as 40 per cent. "Those sorts of things would be absolutely devastating - they would be catastrophic" she said. "There's a widespread view that four degrees could be incompatible with organised global community and would inevitably lead to conflict and disruption and could potentially be beyond adaptation. Ecosystems are already being threatened - at four degrees we have irreversible impacts on ecosystems."

According to the research, 90 companies on the list of top emitters produced 63% of the cumulative global emissions of industrial carbon dioxide and methane between 1751 to 2010, amounting to about 914 gigatons of CO2 emissions. Aside from seven cement manufacturers, the rest of the emitters were [large] energy companies producing oil, gas, and coal.

America, we need to talk.
Have a seat.
Remember when President George W. Bush told you seven years ago that you’re addicted to oil?
It’s time to get serious about your problem. So here’s a little tough love.

That’s it. That is the logic behind the pervasive view on climate change on the right: We don’t like the solutions to this problem, so we officially declare this not to be a problem.

Whitehouse concluded that ignoring climate change was not only bad public policy, it was also immoral. He said God would not grant humanity amnesty from its own folly.

But what if some of those [fossil fuel] reserves can never be dug up and burned? ... If governments were determined to implement their climate policies, a lot of that carbon would have to be left in the ground...

"It feels like the inevitable march toward disaster," said Maureen E. Raymo, a scientist at the Lamont-Doherty Earth Observatory, a unit of Columbia University.

These villages, whose residents are nearly all native Alaskans, are already experiencing the flooding and erosion that are the signature effects of climate change in Alaska. The residents of a number of villages - including Newtok - are now actively working to leave their homes and the lands they have occupied for centuries and move to safer locations.

At the meeting, "Water in the Anthropocene," the scientists said that the of over-pumping of underground aquifers, soaring populations, pollution, the over-use of fertilizers, and climate change are seriously threatening supplies of freshwater around much of the globe. Continuing on the current path will mean that most of Earth's population "will be living under the handicap of severe water pressure," the scientists said, adding, "This handicap will be self-inflicted and is, we believe, entirely avoidable."

There are uncertainties about climate science such as tipping points and feedback effects. But these pale in comparison to the biggest source of uncertainties: people. Here are some of the major things we don't know and really can't know about future society.