5 ways to think about the remarkable slowdown in global CO2 emissions

For much of the past century, the rate at which humans pumped carbon dioxide into the atmosphere increased inexorably year after year, and it seemed like we’d never make any progress on this big honking climate change problem.

But over the past three years, something genuinely shocking has happened. Global CO2 emissions from energy have stayed flat, even as the world economy has kept chugging along, according to a new report by the International Energy Agency. It’s the first time that’s happened without a sharp economic slowdown (as in the early 1980s):

(International Energy Agency)

This pause in CO2 emissions growth, the IEA says, was driven by “growing renewable power generation, switches from coal to natural gas, improvements in energy efficiency, as well as structural changes in the global economy.” Notably, US energy-related emissions fell 1.6 percent in 2016, thanks to the ongoing shift from coal to cleaner natural gas, wind, and solar. Chinese coal consumption appears to be declining (though stats can be unreliable there), led by a shift away from heavy industry. And Europe’s emissions stayed flat last year.

This is a big deal! But we’re still a long, long way from getting a handle on global warming. So here are five ways to think about this chart:

1) If the world wants to act aggressively to stop climate change, this is something to build on. That’s the hopeful news. Most scenarios for limiting total global warming to anywhere close to 2°C — the threshold broadly considered “dangerous” — envision global CO2 emissions peaking by 2020 and falling sharply thereafter. That’s still within our grasp, assuming we take further action. (A big if, as we’ll see.)

2) It’s a bit misleading to say the world has severed the link between CO2 emissions and economic growth, as the IEA implies. We still rely overwhelmingly on fossil fuels to power modern civilization, and if economic growth had been faster last year, emissions would’ve risen. As economist Robert Stavins says of “decoupling” claims, you have to consider the counterfactual. So CO2 could still rise in future years with further growth, particular as low-income countries get richer and build more cars and power plants.

More precisely, what’s happened is that the world now needs to emit somewhat less CO2 to produce a given level of GDP than it used to. In technical terms, the “carbon intensity” of the global economy is falling. We’re using cleaner fuels, and we’re more efficient at extracting value from the fuels we burn. But that process has to accelerate massively if we want CO2 emissions to drop as the economy keeps expanding.

This report from PricewaterhouseCoopers offers a nice way to envision this. Global carbon intensity fell 2.8 percent in 2015 — faster than the average between 2000 to 2015. That’s great. Except … to stay below 2°C of warming, carbon intensity would have to fall a whopping 6.5 percent every single year between now and 2100:

(PwC)

That’s a staggering pace — a pace France managed briefly when it rapidly scaled up its nuclear program in the 1970s, but that few other countries have ever matched. Even the climate pledges from various nations under the Paris climate deal only envision a 3 percent annual drop in carbon intensity. There’s a lot more work to do.

3) Climate action is still mostly confined to electricity. Right now, the bulk of progress on decarbonization is being made in the electricity sector, as this report from France’s Institute for Sustainable Development and International Relations (IDDRI) explains. Countries are replacing dirty coal plants with cleaner natural gas plants, hydropower dams, nuclear reactors, solar arrays, or wind farms. This is low-hanging fruit. You can swap in a gas plant for a coal plant and no one really notices the difference — except CO2 has fallen in half. Simple but effective.

The catch, however, is that electricity is only about one-third of global emissions. And, as IDDRI notes, we’ve made much less headway in the other sectors. Gasoline- and diesel-fueled cars still dominate roads worldwide, and electric vehicles remain a tiny (though growing!) market share. The world still relies heavily on natural gas and oil to heat buildings. And there’s been little progress in cleaning up industrial processes for cement, steel, and iron that are highly carbon-intensive.

Deep decarbonization means changing all of that — electrifying sectors that can be electrified (like heating or transport) and advancing cleaner technologies for the rest (like carbon capture for cement, or biofuels for airplanes). Plus dealing with forestry, agriculture, and so on. In many cases, we’ve barely begun.

What’s more, even the encouraging progress seen recently in the electricity sector won’t continue indefinitely without further, drastic changes. It’s fairly simple to build a gas plant instead of a coal plant or to add modest shares of wind and solar. But massively expanding renewables and ultimately zeroing out gas requires reworking grids and utility models. Scaling up nuclear power requires serious policy changes and/or technical innovation. Dealing with the world’s thousands of existing coal plants means either retiring them early or deploying carbon capture and storage. As Jesse Jenkins and Samuel Thernstrom explain in this new paper, it’s not too hard to cut electricity emissions by, say, one-half with existing technologies. But getting to zero will require dramatically new approaches.

4) This is a good framework for thinking about Donald Trump. Trump, recall, wants to dismantle US climate policies and slash clean energy research. In the short term, that probably won’t hamper the incremental decline in US emissions already underway, as natural gas and renewables keep pushing out coal in the power sector. (Indeed, Trump’s desire to export the newfound abundance of US natural gas might even help nudge down emissions further in places like Europe, by further crippling coal.) But Trump’s policies could easily hinder the push for deep decarbonization, which is what’s ultimately necessary to stop global warming.

5) Don’t forget methane. The IEA chart at the top of this post shows carbon dioxide emissions from energy — which account for roughly 75 percent of all man-made greenhouse gases. But it’s obviously not the only source. There’s also CO2 from deforestation and land-use change to consider, another important chunk.

There’s also methane, which is about 86 times as potent as trapping heat over a 20-year period as CO2. And as two recent studies found, methane concentrations in the atmosphere have been rising at an alarming clip:

(Saunois et al. 2016)

Mysteriously, no one’s exactly sure where all this new methane is coming from, though the expansion of agriculture throughout the tropics remains a prime suspect, particularly new rice paddies and cattle pastures. Methane leaks from growing oil and gas operations may also be a smaller (but important) contributor here.

The good news is that scientists and companies are slowly developing techniques for controlling methane: infrared cameras to detect (and help plug) methane leaks from natural gas pipelines; new types of feed that cause cows to belch less (no, really); even new genetically engineered rice varieties that don’t transfer as much methane from flooded paddies into the atmosphere. It’s solvable. And methane lingers in the atmosphere for a much shorter period than CO2, so action here would show quick results.

Even so, it’s a reminder of what a vast, multi-faceted challenge climate change poses.

Further reading

• The IEA also has a good report on what’s needed for “deep decarbonization” to stay below 2°C. By 2050: “Nearly 95% of electricity would need to be low-carbon” and “7 out of every 10 new cars would need to be electric, compared with 1 in 100 today.”
• Here’s a primer on why 2°C became the red line for international climate negotiations — as well as a discussion of what to do if we skate past it. (Note that the math on staying below 2°C looks increasingly brutal.)
• One final technical note: Carbon concentrations in the atmosphere rose at a record level in 2016, even though man-made emissions stayed flat. What gives? One factor here is that El Niño, which warmed the Pacific, likely affected CO2 uptake by the oceans — so more of the extra CO2 we emitted ended up in the atmosphere. That doesn’t change the big picture here, but it’s a wrinkle worth observing.
• Also note that atmospheric concentrations of CO2, currently hovering around 405 parts per million, will increase every year until we get net human emissions down near zero. It’s like a bathtub — you can slow the flow from the faucet, but the tub will keep filling until the faucet gets turned off completely.

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