The planet endures its hottest summer on record — for the second straight year

The Thompson fire burns over Lake Oroville, California on July 2, and a heatwave sent temperatures soaring resulting in red flag fire warnings throughout the state. (Josh Edelson/AFP/Getty Images via CNN Newsource)

Summer broke global heat records for the second straight year, scientists have confirmed — putting 2024 firmly on track to be the hottest year in recorded history.

The period between June and August — summer in the Northern Hemisphere — was the world's hottest such period since records began in 1940, according to data published Friday by Copernicus, Europe's climate change service.

This summer was 0.69 degrees Celsius hotter than the 1991 to 2020 average, edging past the previous record set last summer by 0.03 degrees, Copernicus found.

It is the latest in a slew of global heat records to fall but will not be the last, scientists warn, as humans continue to pump out planet-heating fossil fuels and drive up global temperatures.

The impacts, and the toll on human health and lives, have been clear, as countries across the world endured brutal summer temperatures, fueling deadly heat waves, record-breaking wildfires and destructive storms.

Even in the Southern Hemisphere's winter, heat has been extreme.

Last month, Australia broke its national record for the hottest August day, clocking a temperature of 41.6 degrees Celsius (106.9 Fahrenheit). Meanwhile, temperatures in parts of Antarctica climbed 50 degrees Fahrenheit above normal in July.

The Copernicus data confirms what seemed likely after the planet experienced its hottest June on record, followed in July by its hottest single days on record.

Summer was capped off by the joint-hottest August on record, Copernicus confirmed Friday.

With an average temperature of 16.82 degrees Celsius (62.28 Fahrenheit), it was 1.51 degrees Celsius warmer than an average August in the pre-industrial era, the time before humans started burning large amounts of fossil fuels.

Taken together, the 12 months from September 2023 to August 2024 were the hottest on record for any year-long period, and 1.64 degrees Celsius warmer than pre-industrial levels, Copernicus found.

"This string of record temperatures is increasing the likelihood of 2024 being the hottest (calendar) year on record," Copernicus deputy director Samantha Burgess said in a statement.

There are a number of factors that cause global temperatures to fluctuate, including natural climate patterns such as El Niño, which originates in the tropical Pacific Ocean and has a planet-warming effect, as well as human-caused factors such as burning fossil fuels — the main driver of the climate crisis.

El Niño, which has helped fuel record temperatures, ended in June, but scientists say its impacts don't stop immediately.

"The record global warmth this summer is expected given the lingering heat from the subsiding El Niño event that has added to the continued heating by emissions of greenhouse gases from human activities," said Richard Allan, a climate science professor at the University of Reading in the UK.

It's "extremely alarming" that the past 12 months breached 1.5 degrees Celsius above pre-industrial levels, Allan told CNN, but said it was "inevitable given the slow pace of action by governments" to cut planet-heating pollution.

Scientists have long-warned that the world needs to limit global warming to 1.5 degrees above pre-industrial levels to stave off the most catastrophic impacts of climate change.

While they are more concerned with long-term breaches — over decades rather than single years — the steady drumbeat of temporary breaches is an alarming indication of where the world is headed, and what that means for people's lives.

Copernicus' Burgess warned of much worse to come.

"The temperature-related extreme events witnessed this summer will only become more intense, with more devastating consequences for people and the planet unless we take urgent action to reduce greenhouse gas emissions," she said.