“Alarming levels of inaction.” That is what the World Health Organization said Wednesday about the global response to coronavirus.

It is a familiar refrain to anyone who works on climate change, and it is why global efforts to slow down warming offer a cautionary tale for the effort to slow down the pandemic.

“Both demand early aggressive action to minimize loss,” said Kim Cobb, a climate scientist at the Georgia Institute of Technology who was teaching classes remotely this week. “Only in hindsight will we really understand what we gambled on and what we lost by not acting early enough.”

Scientists like Dr. Cobb have, for years, urged world leaders to bend the curve of planet-warming emissions. Instead, emissions have raced upward. Now the consequences are being felt: a three-month-long flood in the Florida Keys, wildfires across a record hot and dry Australia, deadly heat waves in Europe.