Earth’s atmosphere has changed profoundly since the first Earth Day

Update April 21, 2023: Earth’s atmospheric carbon dioxide levels averaged over 417 ppm in 2022(opens in a new tab)and even recently reached a daily value of over 424 ppm(opens in a new tab). When this story was first published in 2019, CO2 levels were around 412ppm. They keep rising, relentlessly.

When Americans celebrated the first Earth Day on April 22, 1970, the planet’s atmosphere was markedly different than it is today. Scientists measured 50 years ago(opens in a new tab) Earth’s carbon dioxide levels — the planet’s most important greenhouse gas — is around 325 parts per million, or ppm.

Now, five decades later, that number has risen to about 412 ppm, nearly 90 ppm higher. It’s a change that atmospheric scientists, geologists and climate scientists call unprecedented at least 800,000 years ago, although it’s likely carbon dioxide levels haven’t been this high in millions of years.

“The rate of CO2 increase since Earth’s first day is unprecedented in the geological record,” said Dan Breecker, a paleoclimatologist at the University of Texas at Austin.

“NO No matter how you look at it, it’s completely unprecedented,” agreed Kris Karnauskas, associate professor in the Department of Atmospheric and Oceanic Sciences at the University of Colorado Boulder.

“It’s totally unprecedented”

“The The last time CO2 levels were this high, sea levels were many feet higher than they are today,” added Matthew Lachniet, a climate scientist at the University of Nevada in Las Vegas. This was a warmer geological period on Earth called the Pliocene. About 2.5 to 5 million years ago, Earth’s oceans were about 30 feet higher, Lachniet noted, after the planet’s ice sheets melted at sea.

How unprecedented are today’s CO2 levels?

Earth’s CO2 levels have certainly fluctuated over the past million years, but they’ve naturally fluctuated between 180 and 280 ppm, explained Jason Briner, a paleoclimatologist at the University of Buffalo.

CO2 values ​​for the last 800,000 years
Photo credit: Scripps Institution of Oceanography

But on Earth Day today we even “surpassed” the highest upper limit of natural CO2 fluctuations by about 130 ppm. In short, it’s not normal. Especially in the last 49 years, since the first Earth Day.

“Damn it,” said Briner. “87 ppm in 49 years.”

The CO2 rate is not only very high – it is picking up speed

In the 1970s, after the first Earth Day, CO2 levels increased by about 1 ppm per year. But in recent years, the rate has increased to more than 2 ppm on average, Karnauskas said. This rate is unheard of in the last 800,000 years (scientists have direct evidence of Earth’s CO2 levels from 800,000 years ago from air bubbles trapped in ancient ice(opens in a new tab).)

Previous increases in carbon dioxide levels were simply more gradual events. “Past climate change pales in comparison,” Karnauskas said.

The earth cannot keep up with these changes

We are pumping colossal amounts of CO2 into the sky of the planet.

Normally, the earth can handle this excess carbon. Over time, the planet absorbs carbon into the oceans and rocky subsoil. But today these changes are happening too quickly. The planet simply cannot consume the CO2 glut.

If the rate of CO2 release is as fast as it is now, that carbon will be gobbled up by the oceans, Breecker explained. Today, about 31 percent of man-made CO2 is absorbed into the oceans. But at such a rapid rate (especially since Earth’s first day), the ocean’s surface can only absorb so much carbon dioxide at a time, while the rest stays in the air, warming the planet.

When Earth has more time to deal with increases in CO2 — say, on the order of hundreds of thousands of years — that carbon will also be stored in rock(opens in a new tab)in a well-understood process called “silicate weathering”.

Increasing CO2 ppm since about 2005
Photo credit: NASA/NOAA

But today, these slow natural processes don’t have time to deal with historically high greenhouse gas emissions.

“The rate of CO2 emissions is very important,” Breecker said. “It influences how much of the emitted CO2 remains in the atmosphere and thus contributes to warming.”

Where we are going

Without significant and ambitious efforts to reduce CO2 emissions this century, we could exceed 500ppm.

How much warming is ahead as more heat-trapping carbon accumulates in the atmosphere? Thankfully, climate scientists are now saying we’re not on the worst “business-as-usual” warming trajectory(opens in a new tab) (the red line below) no longer because nations have made efforts and committed to reducing emissions. But significant warming can still occur.

“Implementing the current pledges will only reduce this to a temperature increase of 2.4 to 2.6°C by the end of the century, for conditional or unconditional pledges,” according to a 2022 UN report(opens in a new tab). Important NOTE: 2.4 C equals 4.3 F. And 4.3 F is tremendous warming. Already at about 2 F(opens in a new tab)massive Antarctic glaciers have destabilized and the US faces about another foot of sea level rise by 2050.

This 4.3F warming is more in line with a “medium” emission scenario(opens in a new tab) (yellow line below), with global carbon emissions really starting to decline around 2045. With quick cuts, the line will fall sooner.

The red line shows a scenario with high CO2 emissions.
Credit: BOB KOPP / ECONOMIC RISKS OF CLIMATE CHANGE: AN AMERICAN PROSPECTUS

The UN has made it clear that society needs to be radically decarbonised to spare the future from the worst effects of climate change. “The next few years are probably the most important in our history,” said Debra Roberts, an environmental scientist and lead author of the latest UN climate report(opens in a new tab).

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But with well over 400 ppm and rising, we are already fixated on significant future warming. “Earth will continue to warm for centuries to come,” Lachniet said. “The planet is taking a while to catch up.”

“Scary times ahead.”

More heat promises a stronger drought and extreme, violent weather. But limiting the carbon load on the planet – say below 500ppm – will be a boon for today’s children and for humanity beyond.

“The choices we make or don’t make today will affect the climate 1,000 years from now,” Lachniet said. As things stand now on Earth Day, the trends and magnitude of CO2 increases since 1970 do not bode well.

“Scary times are ahead,” Briner said