After a couple decades of dramatic economic growth, China (with its population of almost 1.4 billion) is now emitting more greenhouses gas than any other single nation. That means that China’s emission trends are incredibly important to watch if you care about the future of climate change. After China signed onto the Paris Agreement in 2015 and pledged to ensure its emissions would stop increasing by 2030, a surprising thing happened: it became apparent that China’s emissions had already dropped.

So what’s going on? Has China met its pledge 15 years early or is this just a bump in an otherwise rising road caused by a temporary economic downturn? Much has been made of this question, and a team of researchers led by Dabo Guan and Jing Meng added a new analysis to the discussion this week.

The team’s first step is to update annual emissions totals (through 2016). A number of different groups have produced estimates, and this updated version comes in at the low end. It also makes 2013 stand out as a slightly stronger peak, with 2014-2016 clearly lower.

To get into the cause of that change, the researchers broke out a number of factors. Population growth and economic growth are obvious possibilities, but the researchers also looked at the mix of fossil fuels being used (including different types of coal) and trends in industry.

First off, many industries have become more efficient with their energy use. Between 2013 and 2016, the efficiency of cement, brick, and glass production improved by 20 percent, for example. At the same time, China has rapidly shifted away from heavier industry and toward tech manufacturing and services. The result is that China’s economy is less reliant on fossil fuels—energy use per unit of GDP has gone down.

China has also closed many older, dirtier coal plants and cancelled plans for a number of new ones, shrinking coal’s contribution to the electric grid. Total energy use increased between 2013 and 2016, but added renewables and nuclear actually covered the growth.

The researchers estimate that economic growth between 2013 and 2016 on its own would have increased emissions by 18 percent, but this was cancelled out by the shift toward cleaner industry and reduced coal usage. Add in all the smaller factors and you get a 4-percent drop in emissions.

The effect of economic growth has slowed over the past decade, but the changes within the economy are actually more significant. The researchers ran a statistical analysis to look for any “changepoints” where trends show a clear break, and 2015 pops out. There appears to be a structural change in China’s economy around this time—not just a lull in growth.

Does that mean China’s emissions will continue to slowly fall from here on out? Not necessarily. In fact, early estimates indicate that China’s emissions rose in 2017—likely due to a combination of higher economic growth and lower hydroelectric generation in a dry year. That isn’t captured in this study, which only has data through 2016.

It is also true that China has grabbed some low-hanging fruit in retiring the oldest and dirtiest coal plants and factories, which you can only do once. After that, continued reductions could get increasingly difficult.

But the researchers highlight several reasons that progress is likely to continue, even if year-to-year fluctuations mean 2013 won’t be the final emissions peak. The structural changes to China’s economy and energy system are not accidental. They’re the product of coordinated national policies.

The government has faced public pressure to improve air and water quality following decades of dirty growth, which is tightly linked to greenhouse gas emissions. And in addition to pushing the shift toward cleaner industries, China is also enacting a national CO 2 emissions trading scheme this year.

“Both emissions and their underlying drivers will need to be carefully monitored,” the researchers write, “but the fact that China’s emissions have decreased for several years—and more importantly the reasons why—give hope for further decreases going forward.”

Nature Geoscience, 2018. DOI: 10.1038/s41561-018-0161-1 (About DOIs).