In the study, the researchers looked at the energy used to power the movement and storage of information online. They did not look at the electricity needed to power phones, tablets and computers.

Eric Masanet is the study's lead author. He is a professor of engineering at Northwestern University in Illinois. In 2018, Masanet and his team looked at the amount of energy that data centers use in the United States. But their new study looks at the amount of energy that data centers use across the globe.

Masanet said that data centers have seen 20 percent energy improvement per year. This is better efficiency than any other industry, he said. Energy efficiency means reducing the amount of energy used on a certain task and getting the same result.

The improvements in energy efficiency are due to better servers and other new technologies. There has also been a shift to cloud computing, in which servers on the internet store and manage data, rather than servers in data centers.

Today, the best estimates are that data centers represent about 1 percent of global electricity use. That's the equivalent to the yearly electricity use of 20 million U.S. homes, said Masanet.

"It's not insignificant, but we don't need to hit the panic button just now," he said.