CO2 emissions fell dramatically after the economic meltdown in 2008. Emissions bottomed out in 2012. There were small increases 2013 and 2014.

I will examine the Nature Communications paper below, but first let's look at the recent carbon dioxide emissions decline in the United States. I'll also look at the bullshit politicians and mainstream journalists come up with to explain that decline.

That statement is touchingly naive, but is undoubtedly an accurate assessment of the situation. On the other hand, what if no one wants to talk about the most important factors behind the emissions decline in the United States?

If we don’t understand the factors that led to this emissions reduction, we won’t know how to effectively reduce emissions in the future.

A recent paper which appeared in the journal Nature Communications has not gotten nearly the attention it deserves. This is not surprising in so far as the conclusions of those who wrote it are not compatible with human expansion on this planet. The paper is called Drivers of the US CO2 emissions 1997–2013 , and one of the co-authors was quoted in a Climate News Network story as follows:

Our politicians have of course taken credit for the declining emissions trend

Building on the strong progress made under President Obama to curb the emissions that are driving climate change and lead on the international stage, today the United States submitted its target to cut net greenhouse gas emissions to the United Nations Framework Convention on Climate Change (UNFCCC). The submission, referred to as an Intended Nationally Determined Contribution (INDC), is a formal statement of the U.S. target, announced in China last year, to reduce our emissions by 26-28% below 2005 levels by 2025, and to make best efforts to reduce by 28%.

Those are the current "official" emissions reduction targets of the United States, though other candidates have offered more ambitious plans (graph above).

Nearly all media reports have attributed the emissions decline to the substitution of natural gas for coal, or progress in getting renewables on-line. I will quote only vox.com's Brad Plumer below because he is far and away the best mainstream reporter covering emissions trends in the United States. Unfortunately, being the "best" mainstream reporter on this subject doesn't mean much. Consider the title of Plumer's April report US carbon emissions are rising again. Can Obama push them back down? (April 20, 2015).

Can Obama push down emissions? Really, Brad? Anyway, let's quote that story. (I added the numbering and changed the formatting). I will deconstruct Plumer's coverage at some length because it is instructive to do so.

One of the most promising climate-change stories of the last decade was the steep plunge in US carbon dioxide emissions after 2005. Before then, US emissions had been rising relentlessly for decades. Suddenly, they were falling. (1) That drop was partly due to the U.S. fracking boom, which created a glut of cheap natural gas and spurred utilities to burn less coal for electricity. (2) It was partly due to various clean-energy and efficiency measures. (3) And it was partly making real progress on global warming.

There you have it — one, two, three. Economic factors (growth?, recession?) are not even mentioned. But now Brad reverses himself. Or does he?

So why did emissions rebound in 2013 and 2014? For starters, the United States is no longer in the throes of a massive recession that crimped energy use. The population is growing, businesses are expanding, and people are starting to drive their cars more. That means everyone's burning more oil, coal, and natural gas — still America's three dominant energy sources.

That solitary paragraph turns out to be lip service. Having touched on the economic factors behind changes in emissions, Brad quickly returns to the happy story he wants to tell.

What's more, coal is no longer declining as quickly as it used to. Coal is the most carbon-intensive of all fossil fuels, and back in 2007 it supplied 50 percent of the nation's electricity. Then came the US fracking boom, which created a surfeit of cheap natural gas for utilities to use instead. By 2012, coal supplied just 37 percent of America's electricity, supplanted by gas and some renewables. Since natural gas produces just half as much carbon dioxide as coal when burned for electricity, this caused CO2 emissions to plummet. More recently, however, coal has been making a quiet comeback. Natural gas is no longer as dirt cheap as it was during the early fracking years, which has allowed coal to rebound to about 40 percent of electricity generation by 2014. That has helped nudged emissions back up.

And thus we are back to coal's comeback being the cause of recent small emissions increases in the United States. Let's update the story by looking at A green case for fracking (July 10, 2015).

... With the rise of fracking in Texas, Pennsylvania, Arkansas, and elsewhere, US natural gas production has surged, and many electric utilities have been switching from coal to cheaper natural gas. The Sierra Club embarked on a wildly successful campaign to convince utility regulators to retire hundreds of now-uneconomical coal plants. America's carbon dioxide emissions have fallen 10 percent since 2005 (though shale gas only deserves part of the credit for that). Yet even as this was all unfolding, environmentalists were quickly souring on the fracking boom...

Did you notice that parenthetical throw-away line with a link in it? — (though shale gas only deserves part of the credit for that). If you follow that link, it goes to an EIA analysis called Lower electricity-related CO2 emissions reflect lower carbon intensity and electricity use.

The EIA graphic is self-explanatory. I've added the introductory text.

U.S. energy-related carbon dioxide emissions (CO2) have declined in five of the past eight years. This trend has been led by emissions reductions in the electric power sector. Electricity demand growth has been lower than in the past and at the same time the power sector has become less carbon intensive (measured as CO2 emitted per kilowatthour of generation). Total emissions from the electric power sector in 2013 totaled 2,053 million metric tons (MMmt), about 15% below their 2005 level. U.S. electricity demand has decreased in recent years, as declines in the industrial sector continue to outweigh slight increases in residential and commercial demand. If electricity demand had continued to increase at its rate over the 1996-2005 period, emissions in 2013 would have been roughly 400 MMmt above actual 2013 levels, assuming carbon intensity remained constant. The power sector has become less carbon intensive for two reasons: the substitution of less-carbon-intensive natural gas-fired generation, displacing coal and petroleum generation, and the growth in noncarbon generation, especially from renewables such as wind and solar.

In short, reduced demand growth for electricity accounted for 53% of the reduction in U.S. emissions from the power sector. That decrease came entirely from declines in industrial use of electricity.

Fuel switching (coal => natural gas) and renewables, which count as decreases in the carbon intensity of power generation, account for the rest of the decline. Also bear in mind that only 38% of all U.S. carbon dioxide emissions come from the power sector.



Source

All of which brings me (finally!) to the Nature Communications paper I started off with. A copy of the paper is available here, but for now I will quote the Smithsonian article describing the results.

For decades, the United States increased the amount of carbon pumped into the atmosphere each successive year. But recently emissions have begun to decline, dropping about 11 percent between 2007 and 2013. Some scientists and media reports attributed the change to the rise of hydraulic fracturing, or fracking and the replacement of "dirty" coal with clean-burning natural gas. But a new analysis of national consumption patterns finds that natural gas played only a minor role in the carbon story—the root of the decline can be found in the Great Recession of 2007.

Here is the graph we're interested in. It's complex, so give yourself a moment to examine it, and read the accompanying caption.



Summary Figure 1 in the Nature Communications paper. From 2007 to 2009, when carbon emissions declined the most, 83 percent of the decrease was due to economic factors, including consumption and production changes. Just 17 percent of the decline related to changes in the nation's fuel mix.

There it is — 83% of the emissions decrease from 2007-2009 was due to economic factors, including consumption (red line) and production structure (blue line). But maybe that's not surprising because the fracking boom didn't really take off until after 2009. What happened after 2009?

From the Smithsonian article again (emphasis added).

After 2009, as the economy began to recover and Americans started consuming goods in greater volumes, carbon emissions decreased by only 0.2 percent each year, on average. At that point, the shale gas boom began to have an effect on carbon emissions. But even then, it wasn’t the biggest factor in the decline. Changes in production and consumption dominated from 2009 to 2011, and after that, a mild winter in 2012 and high gas prices from 2011 to 2013 meant that Americans used less energy overall, emitting less carbon. The Obama Administration has set targets for reducing U.S. carbon emissions by 17 percent in 2020 and 83 percent in 2050, relative to 1997 levels. Getting there won’t be easy. “Further increases in the use of natural gas in the U.S. may not have a large effect on global greenhouse gas emissions and warming, and further emissions reductions due to decreases in energy intensity are not inevitable,” says study coauthor Laixiang Sun of the University of Maryland. The natural gas boom could even make the situation worse. In the short term, gas will compete with renewables, such as wind and solar, notes Hubacek. Plus, coal may be on the decline in the United States, but the nation is still exporting the fuel to China and other countries, which, in effect, exports the resulting carbon emissions around the world.

That's all bad enough, but let's talk about "offshoring" of U.S. emissions. I will now quote the original Nature Communications paper (emphasis added below). You will recall that U.S. power sector emissions declined due to a decline in industrial demand.

Shifts in the production structure [blue line above] of the US economy between 2007 and 2013 have consistently exerted a downward influence used by various industry sectors has evolved and become more efficient (blue bars in Fig. 3). Yet this structural shift also reflects the progressive offshoring of emissions-intensive industries to China and other developing countries over the analyzed period. For instance, between 2009 and 2011, when changes in domestic production structure exerted a downward influence on US CO2 emissions (1%, blue bar in Figure 3 below), we calculated that the net import of emissions embodied in US trade increased by 32% (supplementary Fig. 3). Trade data for the 2011–2013 period is not yet available. [My note— I can not access supplementary Figure 3.]



Contributions of different factors to changes in U.S. CO2 emissions specific to different final demand components, 1997-2013

In other words, the United States "imports" emissions by buying goods from China and elsewhere after the industries which produce those goods have been offshored. The United States ends up "importing" far more emissions than the decline in domestic emissions we get from offshoring.

Detailed Figure 3 and summary Figure 1 reveal that consumption volume (red line) and population (yellow line) are by far the largest positive contributors to U.S. CO2 emissions.

Are we surprised? Not at all. And there is every reason to believe that this observation is also true of every developed or developing nation on Earth. One of the co-authors had this to say:

Steven Davis and his co-authors conclude that without new policies that limit CO2 emissions, it may be difficult to keep emissions down as the U.S. economy continues to recover. And in fact, U.S. CO2 emissions rose in 2013 and 2014. "Lots of people are enthusiastic about the fact that we suddenly have affordable and abundant supplies of natural gas, including many who are concerned about the climate," Davis said. "Our study shows the overriding importance of other factors and warns against wishful thinking."

Yes, "lots of people" (like Brad Plumer) are "enthusiastic" about the switch from coal to natural gas, or the alleged surge in renewables, but it was primarily changes in economic production and consumption which drove emissions levels after 2007. The much ballyhooed emissions decline was predominantly the result of an economy in severe recession, and later, a "recovering" but stagnant economy/ This trend continues today.

Meanwhile, Brad Plumer is now talking about the resurgence in vehicles miles traveled. Americans are hitting the road again, which increases "tailpipe" emissions. Transportation accounts for 32% of total U.S. emissions (by sector, see the graph above), but Plumer only mentions CO2 emissions in passing at the very end of his story.

Nearly everything journalists write about this issue exhibits a consistent pattern of avoidance and denial. Nobody wants to talk about the real reasons behind U.S. CO2 emissions levels because economic and population growth are untouchable; they are taboo. Which brings me back to my Flatland essays, where I try to explain why humans can't talk about the main factors driving CO2 emissions here in the United States and elsewhere on Earth.

But that was not my subject today.