Carbon Dioxide Levels Have Passed a New Milestone (2024)

Carbon dioxide acts like Earth’s thermostat: The more of it in the air, the more the planet warms.

In 2023, global levels of the greenhouse gas rose to 419 parts per million, around 50 percent more than before the Industrial Revolution. That means there are roughly 50 percent more carbon dioxide molecules in the air than there were in 1750.

As carbon dioxide builds up in the atmosphere, it traps heat and warms the planet.

Every additional amount of carbon dioxide in the atmosphere contributes to more warming, which is why climate scientists stress the need to get to zero emissions.

Currently, carbon dioxide levels are rising at near-record rates.

According to data released by the National Oceanic and Atmospheric Administration’s Global Monitoring Laboratory earlier this month, last year had the fourth-highest annual rise in global carbon dioxide levels.

The long-term rise in carbon dioxide levels is caused by burning fossil fuels, as well as other human activities such as deforestation and concrete production.

But there is also a lot of variation from year to year, which you can see in the chart above.

How much carbon dioxide levels rise in a given year depends on two factors: the amount of fossil fuels burned globally, and the share of these emissions that are absorbed by the land and the ocean.

Consider the first factor: While it’s true that clean energy production is rising globally, so is the demand for energy.

Fossil fuels have made up the difference. This is why global fossil fuel emissions are still at record-high values (with a brief dip during the pandemic). And they stayed high in 2023, according to a projection by the Global Carbon Budget.

Not all of these emissions end up in the air. The ocean and land absorb roughly half of the carbon dioxide that humans emit, while the rest stays in the air, said Glen Peters, a senior researcher at the CICERO Center for International Climate Research.

That one-half figure is an approximation. It varies from year to year depending on weather conditions and other environmental factors, resulting in the jagged lines you see in the chart above. For example, in a warm and dry year with many wildfires, the land may absorb less carbon dioxide than usual.

As the Earth warms further, climate scientists expect the land and the ocean to absorb a smaller share of carbon dioxide emissions, causing a larger share to end up in the air, said Doug McNeall, who studies these effects at Britain’s Met Office.

Xin Lan, the lead scientist responsible for NOAA’s global carbon dioxide measurements, referred to the natural absorption as a “carbon discount.”

“We pay attention to it because we don't know at which point that this discount is gone,” she said.

In addition to carbon dioxide, the levels of other potent greenhouse gases like methane and nitrous oxide are also on the rise, which further contribute to warming.

An exceptional year

2023 was unusually hot, both on land and in the ocean. (The oceans absorb over 90 percent of the excess heat caused by global warming.) It was the hottest year in over 170 years of record keeping, even exceeding scientists’ predictions.

One contributing factor to 2023’s extreme heat was El Niño, a climate pattern that tends to raise global temperatures. During El Niño, warm ocean currents in the Pacific Ocean cause warmer and drier weather in the tropics. This can lead to droughts that slow the growth of trees and increase the risk of wildfires.

When this happens, the land tends to absorb less carbon dioxide, and more of it ends up in the air. Several climate scientists said this may be why last year’s rise in carbon dioxide levels was substantially higher than in the years preceding it.

Getting to zero

The current high emissions levels make the climate goal of limiting global warming to 1.5 degrees Celsius increasingly difficult to reach.

To limit warming to this threshold, experts say countries need to slam the brakes on global emissions and bring them down to near-zero in about a decade. And some are even considering more extreme technological solutions to help bridge the gap.

Even if global emissions were brought down to half of their current value, we would still continue to add carbon dioxide to the air, causing further warming.

“You need to bring them essentially down to zero in order to stop warming,” Mr. McNeall said.

How much more warming will occur depends on how long it takes for this to happen.

On one hand, clean energy investments are booming, and renewable energy production is rising globally. But energy demand is also projected to rise, coal power plants are still being built, and some sectors of the economy — like construction and manufacturing — are harder to decarbonize, making the task ahead a steep challenge.

Even if the world exceeds the 1.5-degree threshold, “every fraction of a degree matters,” Mr. McNeall said.

“The closer that you can get to that threshold, the better.”