Sometimes wonky, technical details really matter.

Such is the case on Friday, with an announcement from the International Energy Agency showing that there was a “decoupling” of economic growth and carbon dioxide emissions in 2014. In other words: the world economy grew, but CO2 emissions didn’t. This was “the first time in 40 years in which there was a halt or reduction in emissions of the greenhouse gas that was not tied to an economic downturn,” said the agency.

For anybody who cares about the planet, that’s very good news. After all, the previously tight link between economic growth and the use of more energy — leading to more emissions — has seemed an almost invariant fact of the modern industrial world. Indeed, observations like these have driven some on the environmental left to posit that economic growth itself is incompatible with environmental protections.

So what changed?

The IEA reports that there were several factors involved — China shifting more to renewables, even as OECD countries also advanced renewable energy and combined that with more energy efficiency.

Certainly, that’s been the story in the U.S. electricity industry of late. “For the first time demand is untethered to GDP,” said Alex Laskey, the president of Opower, which works with utility companies to help them connect with customers. “And that’s because of efficiency, self generation, and so on….we can make do with less.”

You can see as much in this figure from the U.S. Energy Information Administration’s 2014 Annual Energy Outlook, showing declining U.S. energy use on a both per capita basis and in relation to GDP — a trend projected to continue:

Home energy efficiency — our far more efficient fridges, stoves, and much else — is just one of many key factors behind the trend, though.

Another factor, noted Robert Stavins, a leading environmental economist at the Harvard Kennedy School, is that in the U.S. transportation sector, cars are also more efficient (thanks to CAFE standards) even as a number of countries (or U.S. states, in the case of California) are pricing carbon and thus using economic forces to make it more costly to release into the atmosphere.

And there’s yet another key factor, according to Stavins — the natural gas boom in the United States brought on by fracking. “This has, in turn, led to significant increases in dispatch of gas-fired electricity generation, relative to dispatch of coal-fired generation, as well as increased investment in new gas-fired electric generation capacity, and cessation of investment in new coal generation in the United States,” he said.

According to the IEA, in the last 40 years, “there have been only three times in which emissions have stood still or fallen compared to the previous year, and all were associated with global economic weakness.” But the global economy was in good shape last year — and grew 3 percent.

This is how progress in saving our planet is measured — as two lines on a graph that no longer follow one another.

Update: This article was updated to make more clear that while there was more total CO2 put into the atmosphere in 2014, there was no increase over 2013 emission levels. According to the IEA, emissions were 3.2 billion tonnes in both years.