The magazine's endorsement was posted online Tuesday, a day after Trump questioned the science of climate change in relation to the California wildfires. Helmuth said the timing was coincidental and the editorial was written during the past two months.
Biden, the magazine said, “has a record of following the data and being guided by science.”
There was no immediate reply to a request for comment from the Trump campaign.
There's been some pushback. Helmuth said the magazine has been monitoring requests for canceled subscriptions and has received some — many from people who weren't subscribers, anyway.
Conservative columnist S.E. Cupp tweeted that while she agreed with the magazine's arguments and planned to vote for Biden, “I do have mixed feelings on whether this is a good use of scientific clout and credibility.”
University of New Mexico psychology professor and author Geoffrey Miller said that the magazine was betraying 175 years of principled bipartisanship “for the sake of some cheap, short-sighted, opportunistic virtue signaling.”
“I'm old enough to remember when your magazine had some integrity,” he tweeted.
But Helmuth said the magazine has not ignored politics; the Atomic Energy Commission burned 3,000 copies of an issue in the 1950s because of its stance against the hydrogen bomb. The magazine has been running more opinion pieces lately, and, in 2016, wrote an editorial questioning Trump's fitness to be president, although it didn't endorse Hillary Clinton.
“Part of our magazine’s mission is to show people how the world works – whether it’s black holes, evolution, viruses, or systemic racism,” Helmuth said. “We felt it was our duty as part of that mission to warn people that Trump has been disastrous for research, science, health and the environment.”
The magazine hopes it doesn't have to make a presidential endorsement again, she said.
On Monday, Trump was confronted during the California briefing about a need to address climate change, and he said that the Earth would get cooler.
“I wish science agreed with you,” responded Wade Crowfoot, secretary of the California Natural Resources Agency.
“Well, I don't think science knows, actually,” the president said.