Much is being made of a new paper in Nature Geoscience in which the authors recalculate "Emission budgets and pathways consistent with limiting warming to 1.5 °C." Whether the authors are justified in their marginally optimistic conclusions — and there's plenty of debate about that — there really isn't much in the way of policy guidance here. Just look at this money quote in Nature:
“The Paris goal of 1.5 °C is not impossible — it’s just very, very difficult,” says lead author Richard Millar, a climate researcher at the University of Oxford, UK.
Or as Millar and his colleagues put in in their abstract:
Hence, limiting warming to 1.5 °C is not yet a geophysical impossibility, but is likely to require delivery on strengthened pledges for 2030 followed by challengingly deep and rapid mitigation.
Yes, well. Ahem. "Challengingly deep" isn't exactly cause for breaking out the champagne, now, is it? But there is a policy lesson hiding elsewhere in this paper, regardless of just how mind-bendingly difficult it will be to keep temperatures and sea-level rise to manageable levels. What Millar et al. did was delve into the tricky world of short-term climate projections, which rely a heck of a lot on economic and technology factors.
The Nature story addresses the problem at the end.
Uncertainty about the details of humanity’s carbon budget don’t matter so much when scientists are modelling the cumulative effect of greenhouse gases over the course of centuries. But fine details matter a great deal when researchers are looking at what level of greenhouse-gas emissions would bump warming to 1.5 °C, because, in that case, scientists’ goal is to tease out the precise effects of heat-trapping gases over a few decades.
“When we start thinking about really ambitious mitigation goals in the really near term, everything starts to matter,” Millar says.
Consider that last line for a second. "Everything starts to matter." That would include factors like short-lived radiative forcing elements such as fugitive methane emissions. Plenty of climatologists who focus on long-term modeling tend to pooh-pooh the influence of the methane that escapes into the atmosphere before it's turned into CO2 in gas-fired power plants. And that makes sense because methane turns into CO2 in a matter of a few decades, so why worry about it? It's how countries like the US and the UK can claim to have reduced carbon footprints by converting from coal to natural gas.
But in the near-term, say 20 years, methane is 86 times as powerful a greenhouse gas as CO2, so it has a massive potential impact, if only briefly, and even if only a small fraction of the natural gas leaks out from the wells and pipes. Indeed, those lower emission rates from switching to natural gas, while reducing CO2 levels, may actually increase total carbon emissions, in the near-term.
So if what you care about is what happens in the near-term, then natural gas and everything else really does matter. And what happens if the climate forcing resulting from briefly elevated methane emissions is enough to trigger positive feedback loop of carbon release from the permafrost or ocean depths? What are the implications for the expected need for carbon-drawdown technologies once we've peaked emissions, but end up with atmospheric carbon levels that are way too high? These are not esoteric questions.
Besides, from a political point of view, near-term effects are far more powerful motivators of policy-making than is the specter of a miserable world 100 years from now. Why not take advantage of this new understanding that "everything matters" and run with it?
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