As President-elect Donald Trump prepares to take office next week, he will be looking to make good on his campaign promise to create jobs and strengthen the economy. He needs look no further than energy efficiency. A new report shows it’s already supporting at least 1.9 million US jobs.

The energy efficiency industry has a remarkably diverse workforce in the United States, ranging from appliance manufacturers and home retrofitters to cloud-based energy management service providers. But since energy efficiency involves so many sectors of the economy, the government can’t collect statistics on it the way it can for the banking or auto industries. This makes it extremely difficult to quantify how many people are employed in energy efficiency-related businesses, because it’s not as clear as counting the number of people who work in a car factory.

Last month, however, E4TheFuture and Environmental Entrepreneurs released a report that does the best job I’ve seen yet of providing a reliable answer. Using a methodology similar to the one the government uses to produce its official statistics, they found that about 1.9 million people worked full- or part-time on energy efficiency in 2015. They found that total was set to increase by almost a quarter of a million last year, making energy efficiency the largest industry in the clean energy economy. It employs about twice as many workers as the auto industry (including auto parts manufacturers), and almost 10 times as many workers as the oil and gas extraction industry. It’s a big number.

Figuring this out is neither easy nor straightforward (which is why we’ve needed a study like this), and there are some drawbacks to doing it. First, the methodology includes every worker who spent any fraction of time working on energy efficiency. It’s the same standard that the Bureau of Labor Statistics uses to estimate employment by industry, and while about 890,000 workers spend at least half their time on energy efficiency, the number will necessarily include a fair number of workers who spent less. By the very nature of the question it’s trying to answer, the number has to be an estimate. Of all the attempts I’ve seen to get at this answer, however, this one is clearly the best, and it gives us a good number to work with. In addition, the report provides results at the state level, giving us an even clearer look at the efficiency industry.

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