There’s a wonderful old saying that you should never make forecasts, especially about the future. Its origins have been obscured by the mists of time, although it probably began as a Danish proverb and came down to us in various formulations from the likes of the great Danish physicist Niels Bohr, Mark Twain and the greatest of recent philosophers — Yogi Berra.

Unfortunately, we’re going to be spending a lot of time in the future, so forecasts become pretty important — particularly when it comes to accelerating problems like climate change. And so, the wonks of the world have been mapping out various scenarios and running enormous computer models on supercomputers, some of which are so complex that they take more than a year to compute.

One of them — the infamous, high-end RCP8.5 — has been the subject of a festering, sometimes vicious, debate among researchers for years. It suddenly erupted into the public sphere in the past week, after one of the important research consortiums agreed that it, along with the low-end scenarios, would be dropped from their next round of models.

The crux of the matter is that RCP8.5 is really based on emissions of greenhouse gases while what matters to living beings is the impacts of climate change. The RCP8.5 scenario looks implausible in terms of fossil fuel burning, but the impacts are still very much in play. I hear from many of you who use these newsletters in your interactions with people who think climate action should be slowed or stopped, and this controversy is the latest weapon in their arsenal, so let’s get into it.

RCP8.5 was based on a super-high climate pollution pathway. It was always intended to map a “burn it all” world and the upper bounds of burning fossil fuels. When it was originally released in 2011, global emissions had soared 30 per cent in the previous decade. Clean energy was expensive and electric vehicles were mostly golf carts and curiosities. And, in the years immediately after RCP8.5 was published, climate pollution exceeded the worst-case scenario.

But, even in that context, the assumptions were bleak: that the world’s population would soar beyond projections and energy technology would sputter, so we’d burn five or six times more coal. RCP8.5 plotted the climate pollution that would result.

There’s a CanCon sidenote to this backstory. It was a University of British Columbia post-doctoral researcher named Justin Ritchie who showed that the coal-burning assumptions were implausible, requiring more coal than we could ever dig up. Ritchie says that five different journals initially declined to publish the research, which was eventually co-published with UBC professor Hadi Dowlatabadi in 2017.

Nevertheless, the scenario came to be known........

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