The most comprehensive report to date on climate change, drawn from over 9,200 scientific publications and over 2 million gigabytes of data, confirms what some climate scientists have been saying for years now: the warming of the global climate is "unequivocal," and it is "extremely likely" that humans are to blame for most of the rise in temperatures observed since the mid-1900s.
Here, five major points to take away from today's 36-page report, which is a summary for policymakers of the full 2,500-page assessment due out in January:
5. The last 30 years have been hot...
According to the report, each of the last three decades has been warmer than the last, and warmer than any preceding decade since 1850. In the northern hemisphere, the last 30 years, from 1983–2012, have likely been hotter than any 30-year period in the last 1,400 years.
4. ... and it's getting hotter.
The report projects that global surface temperatures are likely going to rise by two degrees by the end of this century, resulting in heat waves, increased rain fall, decreased Arctic ice cover and, of course, rising sea levels. The report actually lays out four different scenarios based on different greenhouse gas concentrations: under the most conservative, the planet should warm by 1.5 degrees, and under the least, by as much as 4.5 degrees.
3. That doesn't mean that global temperatures can't "pause."
A lot of attention has been given to the fact that average temperatures have pretty much stayed the same for the last 15 years, leading some to believe that the planet has gotten as warm as it's going to get. But the report suggests that selecting short, arbitrary time periods can skew the data: "Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends." In particular, the last 15 years began with a very strong El Niño, a temporary warming of surface ocean waters in the eastern Pacific.
2. Greenhouse gases are almost certainly to blame.
The concentration of atmospheric carbon dioxide, methane and nitrous oxide — the primary greenhouse gases — is now at levels that are "unprecedented in at least the last 800,000 years," says the report. CO2 levels are now 40 per cent higher than they were in pre-industrial times, and the ocean has absorbed about 30 per cent of that CO2, causing large-scale acidification. The report concludes that the human influence on the climate system "is clear."
1. Don't look to "geoengineering" to fix everything.
Today's report casts doubt on the prospects for so-called "geoengineering" proposals to deal with climate change. There are still significant limitations that make it difficult for humans to remove carbon dioxide from the atmosphere with technology, it says. And as for solar radiation management, which would attempt to reflect a portion of sunlight directly back into space, the report points out that although it may keep temperatures at bay, it won't do anything to address other effects of high CO2 levels, like ocean acidification.
Back in 2012, climate scientist Michael E. Mann was in the red chair to talk to George about hockey sticks and the relationship between the Canadian government and scientists.