It's possible the world will not manage to mitigate emissions of greenhouse gases, and instead stomp on the fossil fuels and speed up global warming.
That's what it looks like right now, with the black diamonds below representing observed emissions, and tracking towards the upper end of estimates:
Today the world's oldest continuously operating scientific body, the United Kingdom's Royal Publishing Society, published a suite of papers looking at the likelihood of a rise of 4 degrees Celsius (7 degrees Fahrenheit) here on earth this century.
Climate Progress writes it up here, mixing this prospect in with a number of other citations to papers and articles on emissions scenarios, methane release, drought, deforestation, desertification, among other scientific prophecies.
It's well blogged, but as an alternative for those of us unable to keep quite so many thoughts clearly in mind, this post will focus on a single important paper, called
When could global warming reach 4°C?
and attempt to bring forward just three, or perhaps four, of its central points.
First, when it comes to assessing the skill of global temperature projections, authors Richard Betts et al point out that we have a history already, from the last thirty years of estimates and observations:
It is unwise to rely on simulations that are outliers in the distribution—indeed the most extreme members of the ensemble simulated warming of 1°C or above by 2000, while warming observed between 1850–1899 and 2001–2005 was between 0.57°C and 0.95°C, with a best estimate of 0.76°C .
In other words, our best estimates to date have been pretty solid, actually.
Second, a scenario without mitigation cannot be ruled out, given the steady rise of emissions, even in the face of a huge economic downturn:
While it is still too early to say whether any particular scenario is being tracked by current emissions, A1FI is considered to be as plausible as other non-mitigation scenarios and cannot be ruled out. (A1FI is a part of the A1 family of scenarios, with ‘FI’ standing for ‘fossil intensive’.)
And finally, a plausible scenario calls for a 4 degree Celsius rise by 2070:
Our best estimate is that a temperature rise of 4°C would be reached in the 2070s, and if carbon-cycle feedbacks are strong, then 4°C could be reached in the early 2060s—this latter projection appears to be consistent with the upper end of the IPCC’s likely range of warming for the A1FI scenario.