Climate experts warn record May CO2 could send summer 3.5 degrees above pre-industrial levels

Climate experts told Inside Climate News that the average global temperatures in summer may briefly climb to 3.5 degrees Fahrenheit above the pre-industrial benchmark, after atmospheric carbon dioxide set a record in May.

A spike like that would further prove that heat-trapping pollution is moving the planet into increasingly hazardous conditions.

What's happening?

Opening Climate Central's monthly briefing, atmospheric scientist Zack Labe said warming caused by humans is expected to make lethal heat waves worse, strengthen storms, and increase the risk of wildfires. Labe noted atmospheric CO2 levels hit a seasonal peak each May, but this May set a new record, according to NASA data.

Climate Central's reports are also serving as a stand-in for the National Oceanic and Atmospheric Administration's monthly briefings, which were canceled last year following Trump administration budget cuts. Labe and meteorologist Tom Di Liberto are among several members of the Climate Central team who previously worked at NOAA.

Di Liberto said, "We heard from a lot of folks that they missed the NOAA briefings and being able to talk with experts." He added, "We were happy to tap into Climate Central's expertise and combine it with our NOAA experience to bring this to fruition."

Those projections come alongside other warnings from climate researchers. Former NASA climate scientist James Hansen has said 2026 is likely to be the hottest year ever recorded, and the European Union's Copernicus climate service recently said Earth is accumulating heat faster than at any other point in the known record.

Why does it matter?

The concern isn't simply about setting another high climate record; it's about how this will affect people and communities. Higher average temperatures mean worsening extreme weather events, public health, community safety, and overall economic stability. 

May is typically the point in the year when atmospheric CO2 is highest, before growing-season uptake by forests in the Northern Hemisphere temporarily removes some of it. But rising carbon dioxide levels still mean more heat is trapped near Earth's surface, and experts say human emissions are now outpacing that natural seasonal pullback.

As extreme weather becomes more destructive, the damage affects both health and household finances. Severe heat can cause heat stroke, aggravate heart and lung conditions, and make outdoor labor unsafe, while stronger storms, floods, and wildfires can destroy homes, close businesses, harm crops, raise insurance premiums, and force families to relocate or evacuate.

Samantha Burgess, Copernicus strategic lead for climate, said that "nearly all of the warming over the last decade is driven by human activities." University of Leeds climate scientist Piers Forster said Earth's growing "energy imbalance" is especially concerning because it offers one of the clearest measures of the pace of climate change, adding that "it provides a crucial measure of the pace of climate change."

What's being done?

With government updates reduced, non-government scientists are taking on more of the public briefings. Climate Central, Berkeley Earth, and Copernicus still release regular analyses based on global monitoring data, helping preserve public access to climate information even as political pressure on climate science increases.

By tying measures like carbon dioxide levels and the planet's energy imbalance to dangerous summer heat, smoke-filled skies, and storm damage, those reports aim to make the data more tangible. Di Liberto said the format gives experts more space to explain those links between climate change and extreme weather.

Slowing these increasingly frequent and severe seasonal records still depends on the same broad response: burning fewer fossil fuels and moving faster toward cleaner energy.

Forster said, "Without human influence, it should be close to zero … but it has doubled in recent decades."

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