CO2 is heavier than air, which means it will sink. If CO2 builds up rapidly, such as at the bottom of a tunnel or in an enclosed room, this gas will push oxygen out of its way. In some cases, this can cause a person — or other animal — to suffocate.
Just like the glass walls of a greenhouse trap heat inside a building’s structure, CO2 acts like a blanket to hold heat close to our planet’s surface. Earth would be largely uninhabitable without it. (The James Webb Space Telescope has discovered evidence of CO2 on an exoplanet. Perhaps the gas helps warm that distant planet as well.)
Mars, by contrast, is very cold — partly because it’s not massive enough to hold onto much of an atmosphere. Thus, Mars simply can’t hold much of the energy it receives from the sun.
For much of Earth’s history, that greenhouse effect has helped the planet maintain temperatures that support life. But there can be too much of a good thing.
In recent years, global CO2 levels in Earth’s atmosphere have risen dramatically — to roughly 415 parts per million. (By January 15, 2023, it was 420.45 ppm at a monitoring station atop Hawaii’s Mauna Loa observatory.) Like a thick blanket, this growing excess traps more heat. And it’s now much higher than most ecosystems have evolved to find comfortable. Instead of feeling warmed on a cool night by a cozy blanket, many organisms now feel as though they’re lying under a pile of thick blankets in the middle of summer.
In recent decades, Earth’s greenhouse effect has shown signs of being out of control. That’s long been an issue on Venus. Its thick, dense atmosphere has led to surface temperatures that average a blistering 453° Celsius (847° Fahrenheit). That’s hot enough to melt lead. Despite its proximity to the sun, the surface of Venus would be far cooler if the planet had only a thin, Earth-like atmosphere.
For much of history, Potosnak says, levels of CO2 in the air have risen and fallen naturally. There has been a relative balance between the sources that spewed it and the processes that removed it. But things have changed. Burning fossil fuels, such as coal, oil and gas, releases lots of CO2. Those fuels power our cars, electronics and more. “Now,” Potosnak says, “we’re amping up that natural [CO2 release] process so fast that it’s throwing our systems out of whack.”
Increases in CO2 levels that “should take thousands of years,” he says, are developing within decades. That’s shown by the dramatic and seemingly skyrocketing “Keeling curve.” This graph of CO2 levels shows them climbing steadily over the past several decades. (The curve gets its name from scientist Charles David Keeling, who collected a lot of the early data.)
Indeed, from 1990 through 2021, “the warming effect on our climate … by long-lived greenhouse gases rose by nearly 50 percent, with CO2 accounting for about 80 percent of this increase.” The World Meteorological Organization, part of the United Nations, issued those findings on October 26, 2022. A year earlier, it pointed out, CO2 concentrations had reached 415.7 parts per million in air. That’s 49 percent higher than before the Industrial Revolution, when use of fossil fuels started to really take off.
It’s now known that humanity’s use of fossil fuels has changed the balance of our ecosystems. That’s causing “a whole cascade of problems,” says Potosnak. “What should take thousands of years, we’re doing within decades by burning so much fossil fuels.
https://www.snexplores.org/article/explainer-carbon-dioxide-source-chemistry-greenhouse-gas-climate#:~:text=CO2%20is%20called%20a%20trace%20gas%20because,too%20cold%20for%20most%20organisms%20to%20survive.
