It is time to take stock of our current climate trajectory, and consider what it means for climate policy. In Part 1 of this week long series, we argued that our current climate trajectory means we must 1) redouble efforts to reduce CO2 emissions as quickly as possible, and 2) we must proactively build resilience to the uncertain impacts of a changing climate. Part 2 examined why voluntary economic contraction is a not a viable strategy for reducing emissions “as quickly as possible.” Part 3 explained why implementing a robust clean energy innovation strategy is the key way to making clean energy cheaper than fossil fuels, thus enabling the rapid adoption of low-carbon energy sources and drastically reducing CO2 as quickly as possible. Part 4 discussed why adaptation through innovation is central to preparing for the impacts of a warmer world. Finally, Part 5 discusses how reducing a set of non-CO2pollutants and greenhouse gases can make a significant, near-term dent in warming and buy time to decarbonize the energy system.
As we have argued previously in this series, averting as much dangerous climate change impacts as possible hinges on our efforts to drive innovation and make clean energy cost competitive with fossil fuels. The cost of decarbonization is the key moderating force affecting the pace of carbon dioxide (CO2) reductions, and innovation is the key to lowering these costs and accelerating climate progress. However, CO2 isn’t the only powerful contributor to global warming, and scientists have identified opportunities to make a significant, near-term dent in warming by tackling other greenhouse gases and pollutants.
While we cannot effectively manage human impact on the climate over the long-run without decarbonizing the global energy system — a task that hinges on the energy innovation efforts described in Part 3 of this series — in the short term, we would do well to seize opportunities to reduce non-CO2emissions, particularly those with immediate co-benefits (e.g. profitable byproducts, improved public health, or better agricultural yields) that align incentives for rapid action.
Scientists estimate that at least 30 percent and as high as 50 percent roughly 30-40 percent of the manmade increase in average global temperature measured to date is a function of climate destabilizers other than CO2, including methane, soot, tropospheric ozone precursor gases, and deforestation. These non-CO2 factors will remain significant contributors to global climate change in coming decades.
This month, an international team of two dozen climate scientists publishedtheir latest findings, indicating that aggressively tackling soot and methane emissions, the #2 and #3 most potent contributors to climate change (after CO2), could reduce the amount of global warming in 2050 by 0.5°C. Methane emissions derive mostly from landfills, agriculture (particularly rice farming), livestock, and natural gas and coal extraction, while soot, otherwise called “black carbon”, results from the incomplete combustion of fossil fuels and derives primarily from primitive cook stoves used throughout much of the developing world, as well as diesel engines and coal-burning power plants.
Reducing global warming by 0.5°C may not sound like much, but when it comes to climate change, every tenth of a degree matters, and slowing near-term warming is particularly important to avoid triggering feedback loops that could accelerate further warming. Tackling methane and soot could reduce the scientists’ projections of average warming in 2050 by 40 percent, which could mean the difference between triggering serious feedbacks in the global climate systems or not.
And the best news about methane and soot is that there are numerous ways to effectively control these two climate destabilizers, often at minimal initial costs and with large near-term benefits.
All 14 of the best methods to reduce methane and soot identified by the team of scientists — including capturing methane at landfills and coal mines, cleaning up cook stoves and diesel engines, and changing agriculture techniques for rice paddies and manure collection — are already being used efficiently in many places, but are not universally adopted, the study’s lead author, Drew Shindell of NASA, told the Associated Press. That means, just as our colleagues argued in Climate Pragmatism, that there are numerous opportunities to cost-effectively tackle these “no regrets” pollutants “through traditional air pollution regulations, the spread of best practices, and multilateral cooperation.”
Better yet, reducing methane and soot emissions would have significant, near-term benefits in addition to helping mitigate climate change. Cleaning up soot pollution could prevent between 700,000 and 4.7 million premature deaths each year, according to the international team of researchers, while capturing methane from coal mines, landfills, and agricultural waste can yield natural gas, a less carbon intensive and increasingly valuable fuel. The scientists also estimate that aggressively cutting methane and soot could boost agriculture yields worldwide by almost 150 million tons and yield overall net benefits 10 times greater than the initial costs of tackling the pollutants.
Yet for those most concerned about climate change, there’s an added imperative to tackling these non-CO2 climate forces: cutting emissions of soot and methane could be the fastest ways to reduce near-term warming and thus buy critical time to decarbonize the global energy supply system.
It all comes down to basic chemistry: CO2 accumulates in the atmosphere and persists there for a hundred years or more before being sequestered by natural forces or breaking down chemically. The longevity and sheer quantity of CO2 means that over the long term, the cumulative amount of CO2emissions is the biggest and most important driver of long-term warming. However, the corollary of this fact is that driving CO2 emissions downwards now does little to reduce warming in the near-term. All that CO2 already in the atmosphere persists, and it continues to lock us into warming that is taking us closer to climate tipping points.
Not so with methane or soot. Cutting emissions of these two agents will yield almost immediate reductions in total global warming. Methane resides in the atmosphere for only 9-15 years, while black carbon precipitates out of the atmosphere after a matter of weeks.
That means that once we cut back on new emissions, the warming effect of soot and methane begins to abate almost immediately. That’s why climate scientist’s estimate over a 20 year time frame, black carbon has an impactmany thousand times greater than CO2 on a ton-for-ton basis, while methane has a more than 70-times greater warming effect than an equivalent amount of CO2.
If our current climate trajectory has us hurtling towards a world of substantial warming, aggressive reductions of soot, methane, and other non-CO2 climate “forcings” (i.e. nitrogen oxides and fluorinated gases) should be a central component of any climate policy strategy. These are the “fast acting” efforts that can yield critical near-term reductions in warming while delivering substantial co-benefits that justify the relatively modest costs of mitigation. There’s no reason not to act on this front, and fast.