The report lists 15 key findings about the changes at the Earth's northern regions. Fifteen. Here are four that alarmed me particularly:
1) The past six years (2005–2010) have been the warmest period ever recorded in the Arctic. Higher surface air temperatures are driving changes in the cryosphere.
3) The extent and duration of snow cover and sea ice have decreased across the Arctic. Temperatures in the permafrost have risen by up to 2 °C. The southern limit of permafrost has moved northward in Russia and Canada.
7) The Arctic Ocean is projected to become nearly ice-free in summer within this century, likely within the next thirty to forty years.
12) Loss of ice and snow in the Arctic enhances climate warming by increasing absorption of the sun’s energy at the surface of the planet. It could also dramatically increase emissions of carbon dioxide and methane and change large-scale ocean currents. The combined outcome of these effects is not yet known.
That last sentence is -- pardon the expression -- chilling. The real truth of this is we don't know how this will affect the planet. We know what's happening (sea levels are rising as the Earth warms, for example), and we have a good idea why it's happening (despite deniers' claims), but we don't know the long-term effects. All we can say for sure is, they won't be fun.
And speaking of deniers, a claim I've heard bandied about is that a single volcano eruption pours more carbon dioxide into the air than humans do over the course of a year (the time scale may vary depending on the claimant, but as you'll see it doesn't matter).
Guess what? That's totally wrong. As geologist Terry Gelrach points out in a paper in the American Geophysical Union's Eos newsletter (PDF), human contribution to atmospheric CO2 completely outstrips anything the Earth puts out; humans put over 30 billion tons -- that's billion with a b, folks -- of CO2 in the air annually, while volcanoes emit about 0.3 billion tons.
In other words, when it comes to carbon dioxide, humans outgas volcanoes by a factor of 100. As Gerlach points out, light duty vehicles (cars and pickup trucks) put out ten times as much CO2 as volcanoes do alone. In fact, human emission is greater than even what a supervolcano like Yellowstone would put out.
Clearly volcanoes have nothing on us. They're hardly a fluctuation on what we're doing.
So, the next time you hear someone trying to use that unfactoid to deny climate change, let them know what the truth really is.