As office buildings limp their way out of the pandemic, occupancy is slowly picking up after months of near abandonment. Companies are increasingly requiring workers to come back to the office, and many workers are complying, if only a few days a week. Offices are being used, by at least some people, at least some of the time.

That means that offices themselves have to essentially stay in “on” mode, with lighting, IT and, especially this summer, air-conditioning activated for whoever decides to come in.

But if offices are still partly empty, are they wasting energy powering all of those systems? According to new data provided to Fast Company, the answer is a surprising no (with an unsurprising caveat).

The real estate data management company Measurabl tracks energy use in 17 billion square feet worth of buildings around the world. Running the numbers for the office sector across the U.S., Measurabl found that office energy use is generally trending downward.

Comparing the first quarters of 2019, 2021, and 2023 in six major American cities, median energy usage per square foot—or what Measurabl’s data scientists call “energy intensity”—is broadly going down over time.

“The single largest controllable expense in most office buildings, and in most buildings period, is energy expenditure,” says Measurabl CEO Matt Ellis. Better tracking how buildings are being used, he says, allows building owners and operators to know when they can adjust how a series of office floors are being cooled, for example, or turn off the power to entire suites that haven’t held meetings in months.

At face value this all makes sense: fewer people in an office means it requires less energy. But office use is actually on the rise. According to the Back to Work Barometer from building security company Kastle Systems, average office occupancy in the ten biggest cities in the U.S. has risen from less than 20% in early 2020 to more than 50% today. Yet office energy use is going down, according to Measurabl’s data. (Ellis notes that energy intensity is slightly up in 2023 in two of the cities analyzed, Los Angeles and San Francisco, which could be related to a colder and wetter winter on the west coast.)

What this means, Ellis suggests, is that building owners and managers are finally taking a more proactive approach to managing how their buildings use energy.

It’s a big change from what we saw not long ago. In early 2021, Fast Company reported on a somewhat surprising reality in office energy use. At that point in the pandemic most offices were still largely empty, and yet energy use in those offices remained almost the same as it was pre-pandemic. According to Hatch Data, a company that tracked energy use in 2,700 commercial properties in North America, energy use had hit 90% of pre-pandemic levels by the fall of 2020.

Part of the explanation was that energy-wasting practices were legal obligations within the leases of those office buildings. “It’s common for leases to stipulate hours of service delivery, and that service delivery can be as detailed as we will deliver 70-degree Fahrenheit air to your space between these hours,” says Zach Robin, then-CEO of Hatch Data (which was later acquired by Measurabl).

Building managers have gradually moved away from those practices, which Ellis attributes to a growing recognition of the environmental and economic costs of doing nothing. Environmental, social and, corporate governance (ESG) standards are driving much of this energy efficiency, particularly among the large office owners. So are energy efficiency regulations, like New York City’s Local Law 97, which requires certain buildings to meet new energy efficiency and greenhouse gas emissions limits by 2024.

“In the institutionally owned office sector, you’re actually seeing declines in energy intensity and carbon, because they’re capable of actively managing these buildings and they have the capital to do that work,” Ellis says. “They’ve been hearing about this from their investors for a long time, and now as the regulations have shown up they’re fairly well prepared. I worry about everybody else.”

That is the unsurprising caveat to the general downward trend in office energy use. Building owners that aren’t yet tracking their energy use and carbon emissions are likely unable to know when their buildings are using more energy than they need, pumping the air-conditioning in an office floor that’s barely occupied, for example. Those buildings could continue to skew the numbers, burning excess energy that doesn’t match with how they’re actually being used, or, as is probably the case with many, not used.

And that represents a significant amount of space. There’s an estimated 82 billion square feet of commercial real estate in the U.S. “Of that 50 billion is in good shape and has this institutional muscle being built up,” Ellis says. “The rest of it, we’ll see.”