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. 

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."

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.

That's led to rising temperatures and leading to more frequent and extreme weather, like heat waves, floods, wildfires and droughts.

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.

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."