March 1, 2017

U.S. Carbon Sinks Not Nearly as Robust as Thought



On February 15, EPA issued its annual draft U.S. Greenhouse Gas Inventory, covering the years 1990-2015. The good news is that, between 2014 and 2015, U.S. emissions dropped from 6,736 MMT CO2 equivalent to 6,586 MMT (about 2.2%). This reversed the upward trend of the previous two years, when emissions had increased from 6,537 MMT in 2012 to 6,736 MMT in 2014 (about 3%). But this good news was clouded by further data revisions that demonstrate once again how far the United States is from meeting its Paris climate commitments.

Some readers will note that these are not the U.S. emissions numbers they are familiar with. That is because we have concluded that using gross U.S. emissions—the amount of greenhouse gases that are actually emitted—is a far more useful metric than the net emissions figure embraced by climate wonks and, more importantly, international climate negotiators. Net emissions are calculated by taking gross emissions and then subtracting the “carbon sink” activity (things that result in reduced natural emissions or increased natural absorption of CO2).

This is known officially as “Land Use, Land Use Change, and Forestry,” and is referred to by the horrible acronym “LULUCF.” LULUCF is the sum of all the carbon sink capacity of forests,¹ minus increased emissions resulting from various sorts of land use activity such as forest fires, converting land to cropland, etc.  LULUCF is a very important measure for countries like Brazil or Indonesia, where actions to preserve or chop down rainforests can have major impacts not only on a country’s’ net CO2 emissions, but on the entire planet’s emissions balance.

There are two reasons why, in terms of U.S. climate policy, we should ignore LULUCF. First, changes in gross emissions are the only way to measure the effectiveness of climate mitigation policy. Those efforts are entirely geared towards reducing emissions and not, in the United States, towards increasing carbon sinks. Changes in LULUCF—and thus in net emissions—do not tell us anything about whether our policies are actually reducing emissions. More importantly, as we will see, taking credit for assumed reductions in LULUCF in future years clouds the scale of the challenge of what needs to be done about gross emissions.

Second, the LULUCF numbers are simply subject to too many major revisions. Last year, we noted that EPA had originally calculated the 2013 LULUCF value as 882 MMT, then proposed revising it to 682 MMT, and then finally arrived at 784 MMT. That swing is nothing compared to what EPA is now proposing as the 2013 value: 370 MMT. In other words, EPA is estimating that the 2013 LULUCF value was actually less than half of the 784 MMT EPA pegged it at only a few months ago. The same is true for the 2014 value. Last year, EPA put that number at 763 MMT. Now it is 369 MMT, and almost exactly the 366 MMT value EPA is estimating for 2015.

This would not be a problem if the absolute value of the LULUCF number were insignificant. But it is not.  The change in the LULUCF value for 2014 is 394 MMT, equal to 6% of U.S. emissions. By comparison, methane emissions from all the nation’s natural gas pipelines were only 176 MMT. EPA’s change in the extent of U.S. carbon sinks is roughly equal to Italy’s net 2013 emissions.   

We do not mean to criticize EPA or its methodology. On the contrary, these changes show that the agency is valiantly trying to improve the accuracy of their numbers. Calculating how much carbon is absorbed per acre of forest (for each of the myriad forest types and ecologies in the United States), how much carbon is emitted when grassland is converted to cropland, etc., is an intellectually gargantuan—and at the global level, a critically important—task. It seems clear, however, that we do not yet have reliable methodologies to accomplish it.

LULUCF, however, is a significant component of our international commitments. The U.S. commitment at Paris was to reduce net emissions by 26-28% from 2005 to 2025. Because of changes to LULUCF, the 2005 net emissions baseline has fluctuated over the last three Inventories; from 6,438 MMT, to 6,680 MMT, and is now 7,000 MMT, a change of some 562 MMT. In contrast, the gross emission calculation for 2005 (which is also—properly—subject to recalculation) has varied from 7,350 MMT, to 7,379 MMT, to 7,316 MMT. This is a net change of only 34 MMT—more than an order of magnitude, less than the variation in net emissions.

But here’s the problem. The U.S. commitment is to reduce that 2005 number by 26-28% by 2025. Using EPA’s latest numbers, this means the 2025 net emissions target is 5,180 MMT.  The latest U.S. report to the U.N. (issued in early 2016) indicated that gross emissions would fall to 6,580 MMT in 2025 on then-current measures (which included many now or soon to be defunct regulatory actions). If the 2025 gross emissions are 6,580 MMT, and the net emissions target is 5,180 MMT, that means sinks must contribute 1,400 MMT, or close to four times the amount they are currently absorbing in order to meet the Paris target. So, while it is comforting to hear that the Paris Agreement may survive the Trump axe, it has become even more obvious that even if the Obama-era regulatory programs were to go untouched (even the Clean Power Plan), there is no chance the United States would come anywhere near its Paris target.        

Unless necessary, in the future we will be using what we think is the far more useful metric, and encourage our readers to do likewise. Meanwhile, it is clear that the latest numbers mean that there never was any chance of meeting Paris even if Hillary Clinton had won, let alone what will happen once the Trump Administration starts unwinding the Obama climate measures.

[1] Other types of landscapes also store carbon, but in the U.S., forests account for more than 85% of sequestration.