We've been working from a 'carbon budget.' This is a calculation of how much greenhouse gas is already in the atmosphere and how much additional greenhouse gas we can emit if we're to stay within the supposed 2 degree Celsius warming target.
Right now there's nothing we can do about existing emissions and so the focus is on curbing new emissions. And that's where we've hit a major snag.
Joeri Rogelj, research scholar at the International Institute for Applied Systems Analysis in Austria, and European and Canadian colleagues propose in Nature Climate Change that all previous estimates of the quantities of carbon dioxide that can be released into the atmosphere before the thermometer rises to potentially catastrophic levels are too generous.
Instead of a range of permissible emissions estimates that ranged up to 2,390 bn tons from 2015 onwards, the very most humans could release would be 1,240 bn tons.
So, we had our new emissions pegged at 2,400 billion tons of greenhouse gas but the new research shows we have to cut that allowance by half, down to just over 1,200 billion tons.
To meet the old safety target we calculated that some 80% of proven fossil fuel reserves would have to be left in the ground, unburned. The remaining 2400 billion tons of emissions, our future quota, represented that 20% of proven fossil fuel reserves we could use to get us through the transition to alternative, clean energy.
If we're down to just 1,200 billion tons of future emissions that means we can only use 10% of proven fossil fuel reserves, not 20%. In other words, 90% of proven fossil fuel reserves must be abandoned, left in the ground. That multiplies the importance of shutting down the extraction of the highest cost and highest carbon fossil fuels and, yes, that means bitumen.
Here's the thing. These latest numbers are still based on that outdated 2C target for limiting warming. That's a political number that has lost its scientific validity. We now know that to avoid triggering natural feedback loops, runaway global warming, 1.5C is the limit and even that only gives us a reasonable chance.
And so it's crunch time. Brad Wall and even Rachel Notley are going to have to stand down. Justin is going to have to stand up and he'd better be wearing the long pants for this one. He's going to have to shut down the Tar Sands or wear the consequences for all of his cowardice.