We likely sound like a broken record on this issue, but once again there have been developments that cast even more doubt on the ability of the United States to meet the commitments it has made in the Paris climate agreement. Those developments underscore the importance of better monitoring what countries say and do about their emissions, a concept that was included in the Paris agreement but has a very long way to go.

In February we described how EPA’s draft annual U.S. emissions inventory proposed re-calculating both historical emissions and the capacity of “carbon sinks,” such as forests and grasslands. Both emissions and sinks are equally important for purposes of the Paris agreement. The United States has promised to reduce “net” emissions (gross emissions less those absorbed by sinks) by at least 26% from 2005 levels by 2025. “Net” emissions is a reasonable concept, but measuring the size and absorption capacity of carbon sinks is a difficult matter and, at best, a work in progress.

On April 15, EPA published the final version of the 2016 Inventory, which includes data through 2014. The final numbers have been revised somewhat from the draft figures, but not in any material way. The good news is that the final number for net 2014 emissions was smaller—6,108 million metric tons (“MMT”)—than the figure in the draft inventory. The bad news is that this means that emissions grew by 1.1% (68 MMT) in 2014 (from 6,040 MMT in 2013). In other words, we may be back to something close to the “old” relationship between economic growth and emissions.

EPA’s revised net emissions number for 2005 (the Paris baseline) is 6,680 MMT, so the administration’s 26% reduction target means that emissions must come down to 4,943 MMT by 2025. The difference between 2014 emissions (6,108 MMT) and the target is 1,165 MMT, which means the U.S. must reduce its 2014 emissions by 19% in order to meet the target. That is roughly 1.7% per year over the next 11 years.

As we have discussed previously, we simply do not see what regulatory mechanisms are available to achieve this. Any gap between promise and performance would probably lead a Clinton Administration to make the Clean Power Plan substantially more stringent in order to commit to meeting this target by 2030 or so.

But another, potentially larger issue, lurks here: how accurate are the numbers that the United States—and everyone else—will be using to determine both what their Paris commitments are and whether they will have met them?

Back in February, we noted that the biggest change to the U.S. commitment was not increased emissions, but rather the assumed decreased capacity of sinks to absorb CO2. In the previous Inventory, EPA had used 882 MMT as the 2013 sink capacity. That number has now dropped to 784 MMT. But what is more interesting is that in the February draft the 2013 number was only 682 MMT. Thus EPA first calculated 2013 sinks at 882 MMT, then proposed revising that to 682 MMT, and finally arrived at 784 MMT. In 2025, per the December U.S. report to the UNFCCC, they must rise to 1,200 MMT if the target is to be met.

We point this out not to say that EPA is playing with the numbers, but rather to illustrate how difficult it is to make accurate estimates of greenhouse gas emissions and sinks. It is easy to determine what the gross emissions from, say, coal-fired power plants are, because operators continuously monitor their emissions and report those electronically to EPA. It is much more difficult to estimate methane emissions from the more than 300,000 miles of natural gas pipelines across the country or, likewise, how much CO2 an acre of U.S. forestland absorbs in one year.

If the United States is having these sorts of problems, imagine how difficult it is for most other countries that have signed the Paris agreement. The recent ruckus over whether China’s emissions from burning coal are increasing or decreasing shows that even trying to calculate something as relatively simple as smokestack CO2 emissions can be extremely problematic. Do not be surprised if, during the follow-on process to Paris, significant disputes erupt about whether countries have fulfilled their promises or not. The politically dull but environmentally important standardization of reporting methodologies should be very close to the top of government agendas.