CO2 levels just broke another record. Here's what that means
Bridget Stringer-Holden
| CBC News | Posted: June 7, 2025 8:00 AM | Last Updated: June
7
The CO2 concentration at the Mauna Loa observatory in Hawaii
has passed 430 parts per million
Image | Recent portrait of Ralph Keeling in the lab at Scripps
Caption: Geophysicist Ralph Keeling in his lab at Scripps
Institution of Oceanography at University of California San
Diego, where carbon dioxide levels are tested. (Scripps
Institution of Oceanography at UC San Diego)
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When man first walked on the moon, the carbon dioxide
concentration in Earth's atmosphere was 325 parts per million
(ppm).
By 9/11, it was 369 ppm, and when COVID-19 shut down normal
life in 2020, it had shot up to 414 parts ppm.
This week, our planet hit the highest levels ever directly
recorded: 430 parts per million.
For 67 years, the observatory on Hawaii's Mauna Loa volcano has
been taking these measurements daily — tracking the invisible
gas that is building up in our atmosphere and changing life on
Earth.
The record is known as the Keeling Curve. Charles David Keeling
began those recordings, some of the first in the world to
measure CO2 concentration over time.
Image | Keeling Curve
Caption: Measurements of C02 in the atmosphere at the Mauna Loa
Observatory show levels steadily rising — with annual variation
— since record-keeping began in 1958. (Scripps Institute of
Oceanography at the University of California San Diego)
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His son, Ralph Keeling, born one year before the observatory
opened, has witnessed the rapid increase firsthand over his
lifetime.
"I was a teenager when I first started to appreciate what my
father was doing and how it might be significant," Keeling told
CBC News. Back then it was around 330 ppm.
Keeling, a geochemistry professor at Scripps Institution of
Oceanography at the University of California, San Diego, took
over the research once his father passed away in 2005.
"This problem is not going away, and we're moving further and
further into uncharted territory, and almost certainly, very
dangerous territory."
Image | Charles David Keeling
Caption: Charles David Keeling is a U.S. scientist who first
developed an accurate way of assessing atmospheric CO2.
(Scripps Institution of Oceanography)
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Why CO2 matters
The build up of carbon dioxide in the atmosphere isn't visible
to the naked eye, but its concentration matters because of the
greenhouse effect.
Like the glass walls that trap heat from the sun in an actual
greenhouse, gases in our atmosphere such as CO2 and methane
also trap heat from the sun.
At the start of the Industrial Revolution, ice core samples
show CO2 levels were around 280 parts per million but as they
rose, warming has increased by about 1.3 C over the
pre-industrial average.
Image | 800,000 years
Caption: Scientists can calculate the CO2 levels in the
atmosphere from before record-keeping began by using ice core
samples. Over 800,000 years, that data shows fluctuation over
time, but in a limited range — until levels shot up after the
Industrial Revolution. (Scripps Institute of Oceanography at
the University of California San Diego)
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That's led to rising temperatures and leading to more frequent
and extreme weather, like heat waves, floods, wildfires and
droughts.
* Did we surpass 1.5 C of warming in 2024? It depends on who
you ask
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wildfire season in decades
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climate change, expert says
* 2024 was one of the warmest years on record for the
Maritimes
While many have heard about the goals of limiting warming to
1.5 C or 2 C above pre-industrial levels, there have also been
efforts to return CO2 levels to below 350 parts per million, as
a key part of limiting the damage from climate change.
The record highs have continued though. Just in the last year,
CO2 readings from May have increased more than three parts per
million — that many more molecules of CO2 trapping heat and
contributing to warming.
"We know why it's rising faster than ever, it's because we're
burning more fossil fuels each year," said Keeling.
Direct link to fossil fuels
Damon Matthews, a climate scientist and professor at Concordia
University in Quebec, also says he's concerned and isn't
surprised that there are new records every year.
"If we want to actually stabilize CO2 levels in the atmosphere,
we would need to cut global emissions by more than 50 per cent,
and we're nowhere near doing that," he said, adding that there
are other gases at play but CO2 is the dominant influence.
"Every May, we're going to see a new record of atmospheric CO2,
until we actually make a lot more progress on climate
mitigation than we have today."
The annual cycle, peaking in late spring in the northern
hemisphere, is tied to plant photosynthesis — CO2
concentrations drop in the summer as plants absorb the gas and
release oxygen.
* What is the Keeling Curve and what does it tell us about
the health of the planet?
* Ships must limit CO2 emissions under new UN deal
* Carbon dioxide levels hit 50% higher than pre-industrial
time
In 2021, the International Energy Agency said that if the world
wants to limit global warming and reach net-zero by 2050, there
could be no new coal, oil or gas projects.
Matthews is part of Canada's net-zero advisory body and says
he's seen some progress in decreasing CO2 emissions the last
few years, but not enough.
He says Europe's emissions have been going down for decades,
and that last year CO2 emissions in China didn't increase.
However, he says Canada still lags behind other countries, and
the U.S. is trending the other way.
"There's lots of policy options, certainly focusing on
expanding the oil and gas industry in Canada right now is not
going to get us where we need to go in terms of climate," he
said.
"We just need to stop arguing about whether it's a priority and
start doing the things that we know will help to solve the
problem."
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