People walk through cooling misters on June 4, 2024 in Las Vegas. Tens of millions of people from California to Texas are experiencing intense heat. New data shows that the amount of planet-warming carbon dioxide in the atmosphere has hit a new record.

John Locher/AP

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John Locher/AP

The amount of planet-warming carbon dioxide in the Earth’s atmosphere has hit a new record, as humanity struggles to rein in emissions of greenhouse gasses from burning fossil fuels.

The new record comes as tens of millions of people are grappling with extreme weather in the United States. Much of the western U.S. is experiencing the first major heat wave of the year, which is driving temperatures 20 to 30 degrees Fahrenheit hotter than what is normal for June. In the Southwest, temperatures are lingering well above 100 degrees.

Such extreme, prolonged heat is directly related to human-caused climate change, scientists say. All the extra carbon dioxide (CO2) in the atmosphere traps heat, and leads to more intense, frequent and persistent heat waves, and other extreme weather such as powerful hurricanes and heavy rain storms.

“Over the past year, we’ve experienced the hottest year on record, the hottest ocean temperatures on record, and a seemingly endless string of heat waves, droughts, floods, wildfires and storms,” said Rick Spinrad, administrator of the National Oceanic and Atmospheric Administration (NOAA), in a statement. “We must recognize that these are clear signals of the damage carbon dioxide pollution is doing to the climate system, and take rapid action to reduce fossil fuel use as quickly as we can.”

The concentration of carbon dioxide in the atmosphere is measured in parts per million, and measurements are taken at an observatory in Hawaii. In May, the atmospheric CO2 concentration peaks because the gas accumulates more in the winter months when there are fewer leaves worldwide to soak it up.

This May, the concentration of CO2 in the atmosphere hit nearly 427 parts per million, which is an increase of about 3 parts per million compared to last year’s peak. That’s one of the largest annual jumps on record, scientists say.

The vast majority of the planet-warming pollution in the atmosphere comes from humans burning fossil fuels such as oil, gas and coal.

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The amount of carbon dioxide in the atmosphere has been steadily increasing since scientists began routine measurements in 1958. At that time, the CO2 concentration in the atmosphere was 313 parts per million, slightly higher than in the 19th century, when the Industrial Revolution sparked the widespread consumption of fossil fuels.

But in recent years, growth of CO2 in the atmosphere has accelerated. In the first four months of this year, the CO2 concentration increased more quickly than it has during the first four months of any previous year on record, according to scientists at NOAA and the Scripps Institution of Oceanography at the University of San Diego.

Although routine, direct measurements of CO2 in the atmosphere began in the 1950s, scientists are able to use other methods to estimate how much carbon dioxide was in the atmosphere going back millions of years. And there’s more carbon dioxide now than there has been in millions of years.

Rising CO2 levels underscore the degree to which humanity’s collective efforts to reduce greenhouse gas emissions and switch to renewable sources of energy are falling short of what would be needed to rein in global temperatures. In the U.S., greenhouse gas emissions fell slightly last year but those declines do not put the country on track to meet climate targets set by the Biden administration.