“No False Choices: To Preserve A Livable Climate, We Need To Slash Both CO2 And Methane ASAP“
The bad news is that humanity has dawdled for so long that our only realistic chance to avoid multiple, irreversible, catastrophic climate impacts is to slash both carbon dioxide and the “super pollutants” like methane sharply starting as soon as possible.
As Dr. Jeffrey Sachs, Director of Columbia’s Earth Institute, told MSNBCTuesday:
We’ve been told the basic falsehood that somehow fracking is going to save us, which is basically the opposite of the truth.
What kind of good news can the world expect after ignoring near-unanimous expert advice for 25 years? Well, we can almost certainly avert the worst impacts for billions of people, but only by aggressively curtailing both CO2 (which lingers in the atmosphere for hundreds of years) and the super pollutants (which are much more potent at trapping heat in the short-term than CO2, but which have a much shorter atmospheric lifetime).
Some confusion has been generated on this issue by a Tuesday New York Times piece, “Picking Lesser of Two Climate Evils,” which frames our optimum climate strategy as a choice between targeting CO2 and targeting super pollutants like methane, hydrofluorocarbons, and black carbon, that together cause some 40% of the warming we’re experiencing now.
But that is a “false choice,” as longtime NASA climate scientist Drew Shindell explained to me. We have to do both to maximize lives saved and minimize the chances of dangerous warming. That’s a point Climate Progress has made consistently.
The New York Times piece builds off an analysis by climatologist Raymond Pierrehumbert on “Short-Lived Climate Pollution” (SLCP). He concludes that an “implementation of SLCP mitigation that substitutes to any significant extent for carbon dioxide mitigation will lead to a climate irreversibly warmer than will a strategy with delayed SLCP mitigation. SLCP mitigation does not buy time for implementation of stringent controls on CO2 emissions.”
I think that conclusion is correct: Absent an effort to sharply reduce CO2 emissions ASAP, everything else is a sideshow if not an outright distraction.
But I think this assertion by Pierrehumbert is not tenable: “There is little to be gained by implementing SLCP mitigation before stringent carbon dioxide controls are in place and have caused annual emissions to approach zero.” That seems to me a false choice, suggesting that humanity is somehow incapable of reducing all greenhouse gases at the same time.
Also, it ignores the risk that we might cross irreversible warming thresholds in the coming decades that further accelerate warming — such as permafrost melt — before the impact of the CO2 reductions can be felt. And it ignores the very low cost of reducing SLCPs compared to the relatively higher cost of reducing CO2 as you approach zero (i.e. after you have exhausted all of the low-cost CO2-reduction strategies). The SLCPs account for much of current warming, and they must be dealt with.
The case where this matters most is natural gas, since natural gas is mostly methane, leaks at every point in the production and distribution process, but also releases CO2 when burned as a fuel. Methane is a whopping 86 times stronger at trapping heat than CO2 over a 20-year time scale, but “only” 34 times stronger over a 100-year time scale. And, as the IPCC wrote in its recent review of the science, “There is no scientific argument for selecting 100 years compared with other choices. The choice of time horizon is a value judgement since it depends on the relative weight assigned to effects at different times.”
The key point is that using natural gas to replace coal poses risks in all time periods. And, when you do the math based on actual observations of methane leakage, it turns out, as I’ve discussed, “By The Time Natural Gas Has A Net Climate Benefit You’ll Likely Be Dead And The Climate Ruined.”
As Sachs told MSNBC, “We have to move decisively” to carbon-free energy sources, including renewables and even nuclear. “This is pretty basic stuff.”
Here are more of Dr. Shindell’s thoughts on the subject:
I would strongly argue that there are two distinct environmental problems, one is long-term climate change for which CO2 is the dominant driver, and one is the combination of near-term climate change and air quality, for which SLCPs dominate. I don’t believe society is only capable of considering one problem at a time so that putting effort into cutting SLCPs would undermine efforts to cut CO2 — we consider multiple problems all the time (e.g. promoting clean water does not undermine promoting clean air, and there are countless such examples).
Demanding that CO2 reductions be made first, as has been promoted by some of the anti-SLCP crowd, runs the danger of blocking any action on SLCPs for many many years given the dismal state of progress on CO2. That would lead to many premature deaths that could have been prevented, larger near-term climate change that is already affecting people around the world, etc. So there are dangers either way if solving one problem is stalled due to the other, and so it’s important to keep working on both in my opinion. If our leadership can’t manage two environmental problems at once, then rather than choosing one or the other I’d say we should choose new leadership.
SLCP reductions don’t buy time for CO2 reductions, but they do provide more time for adaptation and improve the chances of avoiding tipping points by delaying the time at which we reach them so that if CO2 reductions take place they’ll have more time to have their impact.
Since Prof. Bob Howarth of Cornell has been remarkably prescient in raising concerns about methane leakage, I asked him to comment on Pierrehumbert’s findings:
1) It is a false choice to say we must rely on coal or natural gas. When I conclude the greenhouse gas footprint of natural gas is worse than that of coal on the decadal time scale, I am not arguing for coal. Rather, we should wean ourselves from all fossil fuels, and natural gas is not a bridge fuel towards doing so.
2) He ignores potential tipping points in the climate system which we increasingly run the risk of hitting if we do not reduce methane emissions. If the tipping points are hit, we will have runaway global warming that will be devastating. And we cannot avoid warming the planet to dangerously high temperatures (1.5 to 2 deg C) over the coming few decades by reducing carbon dioxide emissions. We must reduce methane emissions to lower this rate of warming on this time scale.
3) And yes, he ignores the problems with global climate disruption over the coming few decades, apparently feeling any damage on this time scale is OK if we are address the long-term problem.
I think I have done a good job of summarizing these issues and arguments in my May 2014 paper (Howarth, R. W. 2014. A bridge to nowhere: Methane emissions and the greenhouse gas footprint of natural gas.
UPDATE: Dr. Michael Tobis — climate blogger and modeler par excellence — points out that if we just reduce CO2 use sharply, then we would see a short-term boost in warming from the reduction in sulfate aerosols associated with the sharp coal reductions (see here). So that is yet another important reason we need to go after both coal and SLCPs.