Climate and environment updates: Atmospheric CO2 hits highest level in human history

The Earth has hit another climate milestone, and it's a stark reminder that when it comes to climate change, the planet is moving in the wrong direction.

For the first time, the monthly average of carbon dioxide in the atmosphere has surpassed 430 parts per million at the Mauna Loa Observatory in Hawaii. The May 2025 number is higher than it's ever been in human history and marks a significant jump from the previous year.

Scientists from the National Oceanic and Atmospheric Administration and the Scripps Institution of Oceanography at the University of California, San Diego have been taking daily CO2 measurements from the Mauna Loa site since 1974.

"Another year, another record," Ralph Keeling, director of the Scripps CO2 Program, said in a statement. "It's sad."

Carbon dioxide is a key gas in Earth's atmosphere, contributing to the greenhouse effect by trapping heat. Since the Industrial Revolution, its levels have increased due to rising human activities, particularly the emission of fossil fuels.

Researchers at the University of Utah, who participated in a 2023 study with nearly 100 scientists from 16 countries, found that the amount of carbon dioxide in the atmosphere is higher than it has ever been in human history and the highest in at least 14 million years.

The increasing amount of carbon dioxide in our planet's atmosphere has altered the planet's weather patterns and intensified the frequency and severity of extreme events, such as heat waves, droughts, wildfires, heavy rainfall and flooding, according to the Intergovernmental Panel on Climate Change.

-ABC News meteorologist Kyle David

Last month was the second-warmest May on record globally, trailing only the previous May, according to new data analyzed by the Copernicus Climate Change Service (C3S). And in the Northern Hemisphere, spring also ranked as the second-warmest on record, again behind 2024.

Notably, May marked the first month since July 2024 in which the global average temperature did not exceed the 1.5-degree Celsius warming threshold established in the 2015 Paris Climate Agreement. Instead, it registered 1.40 degrees Celsius above the pre-industrial reference period (1850-1900). The Earth's average surface air temperature came in at 60.42 degrees Fahrenheit, or 15.79 degrees Celsius.

A short-term drop in global temperatures was anticipated due to the recent La Niña event in the equatorial eastern Pacific Ocean, a climate pattern that typically brings a temporary dip in global average temperatures. However, climate scientists caution that this pause is unlikely to last, as human-caused greenhouse gas emissions continue to fuel the long-term warming trend.

Global daily sea surface temperatures across much of the world's oceans remained well above average in May, with the second-highest value on record for the month, according to Copernicus.

Unusually warm sea surface temperatures across portions of the Atlantic Basin could play a key role in tropical cyclone development during the Atlantic Hurricane Season, which is now underway. The National Oceanic and Atmospheric Administration (NOAA) predicts that Atlantic tropical cyclone activity will likely be above average this year, citing elevated ocean temperatures as a contributing factor.

-ABC News meteorologist Dan Peck

Researchers at the University of Pennsylvania have discovered a novel method for harvesting water from the air. If the breakthrough can be commercialized, the technology could eventually provide people with fresh water in areas where it's scarce.

According to a report published in Science Advances, researchers created a unique material that traps water vapor from the air and harvests it as condensed water droplets. This new material is a spray-on polymer-silicone composite that can be applied to most surfaces.

The researchers say they came about this discovery by accident. While running other experiments involving polymers and water, a graduate student first noticed water droplets forming where they shouldn't have been.

"This sort of unexpected phenomenon started happening. We got intrigued," said Daeyeon Lee, chemical and biomolecular engineering professor at the University of Pennsylvania and co-author of the report.

Contrary to the researchers' understanding of water droplets, they were surprised to find the water did not evaporate but instead remained on the material's surface.

Researchers initially thought what they were seeing was the result of their local environment, but the water-harvesting feature of the new material was replicated at another lab in the United Kingdom.

"The phenomenon that we were observing was so unusual and unique that we wanted to see if it could be produced in somebody else's hands," said Lee.

While other water-harvesting methods and technologies are available, this material's harvesting method is as close to a passive process as possible, making it incredibly accessible.

"We see these water droplets that are forming on the surface, and we want to see if we can now easily collect this water without spending much energy," said Lee.

Although the product is still in its early stages, this material could eventually be used in water-scarce environments to supply water, and its spray-on form makes it very versatile.

"You can literally imagine this becoming like a paint," said Lee. "Material that you can coat anywhere."

Researchers are now working on developing a fine-tuned version of the material for arid environments.

-ABC News' Charlotte Slovin

Although floods and hurricanes often dominate headlines, extreme heat is the deadliest weather-related hazard in the United States, according to the National Weather Service. And among all the extreme weather events, the science linking climate change to extreme heat is among the strongest and supported by the highest level of confidence.

Now, a new report by Climate Central, Red Cross Red Crescent Climate Centre and World Weather Attribution found that human-amplified climate change is responsible for exposing half the world's population to an additional month of extreme heat.

Researchers examined the role of climate change in extreme heat events over a 12-month period, from May 1, 2024, to May 1, 2025. During that time, 4 billion people experienced at least 30 additional days of extreme heat due to climate change, according to the report, which has not been peer-reviewed. The study defined extreme heat as temperatures warmer than 90% of historical observations at a given location, compared to the average climate between 1991 and 2020.

The analysis also found that climate change at least doubled the number of extreme heat days in 195 countries and territories worldwide compared to a planet without global warming.

Last year was the planet's warmest year on record and the first calendar year in which Earth's global average surface temperature measured 1.5 degrees Celsius (2.7 degrees Fahrenheit) above the 1850-1900 pre-industrial average, a key warming threshold established in the 2015 Paris Climate Agreement.

Released in advance of Heat Action Day, a global day of awareness and action on extreme heat, the authors of the report say their findings should serve as a warning about the dangers of extreme heat.

"These frequent, intense spells of hot temperatures are associated with a huge range of impacts, including heat illness, deaths, pressure on health systems, crop losses, lowered productivity, and transport disruptions," World Weather Attribution researcher Mariam Zachariah wrote in a statement.

While early June does not mark peak heat in all regions, the organization emphasizes that designating a single, coordinated day delivers a strong global message. It aims to help individuals and communities everywhere prepare for the growing risks posed by extreme heat.

-ABC News meteorologist Dan Peck