Carbon Emissions Could Plummet. The Atmosphere Will Lag Behind

Apr 14, 2021
Originally published on April 14, 2021 9:56 pm

In the next several days, the Biden administration is expected to announce plans across the economy to reduce America's greenhouse gas emissions dramatically by 2030.

The Biden administration's goal is to speed the process to avoid a climate tipping point that scientists warn is quickly approaching. If global warming continues at its current pace, rising seas and heavy rain will flood cities around the world, wildfires and hurricanes will become even more destructive, and many more plant and animal species will go extinct.

But reducing emissions, even sharply, will not immediately fix the problems up in Earth's atmosphere. It took decades for greenhouse gases to accumulate in the atmosphere and trap heat, and it will take centuries for those gases to dissipate once humans decide to stop pumping them into the air.

"When you emit carbon dioxide, the climate stays altered for a long time," says Solomon Hsiang, a climate scientist who is the co-director at the Climate Impact Lab at the University of California, Berkeley. "And so we kind of have to deal with that baggage no matter what."

Everyone alive will still need to adapt to a warming climate. Today's adults will be dealing with climate-driven extreme weather for decades to come. But if countries transform their economies to cut heat-trapping emissions sharply, today's kindergartners could inherit a safer world when they reach middle age.

"It's kind of like you're driving a giant train that's very heavy. You slam on the brakes. The train keeps going for a while," Hsiang explains. "There's some amount of heating that we would continue to experience," even with dramatic cuts to greenhouse gas emissions. It will take decades for forests, oceans and other natural systems to soak up all the excess greenhouse gases that have accumulated in the atmosphere.

Why greenhouse gases persist

The major greenhouse gases emitted by cars, trucks, factories, power plants and farms are carbon dioxide, methane and nitrous oxide. The gases make their way up into the upper part of the atmosphere and hang out there, trapping heat and causing global warming.

The good news is that carbon dioxide, methane and nitrous oxide don't live forever in the atmosphere. Eventually, they break down or are absorbed by plants, oceans, soil and rocks on Earth's surface.

But humans have been generating such enormous emissions that new greenhouse gases arrive in the atmosphere a lot more quickly than old emissions break down or are absorbed. That's why gases have been accumulating in the atmosphere extremely quickly, especially in the last 50 years.

Different greenhouse gases take different amounts of time to break down or be absorbed. Nitrous oxide lingers in the atmosphere for about 100 years. Carbon dioxide can persist for hundreds or even thousands of years.

"If we got rid of all emissions tomorrow, carbon dioxide would come down very, very slowly," says James Butler, director of global monitoring at the Earth System Research Laboratory at the National Oceanic and Atmospheric Administration. "It would take thousands of years to come out."

Then there's methane, the shape-shifter of greenhouse gases. Methane only accounts for a small portion of the greenhouse gases emitted each year. But once it's in the atmosphere, methane is extremely good at trapping heat from the sun, which makes it far more potent than carbon dioxide in the short term.

Luckily, methane breaks down relatively quickly. If humans stopped emitting greenhouse gases, it would only take about 100 years for the excess methane in the atmosphere to dissipate, Butler says.

Here's the problem: When methane breaks down, it can turn into carbon dioxide. Both gases have a carbon at their center: Methane has hydrogen atoms attached, and carbon dioxide has oxygen atoms attached. As methane breaks down, the hydrogen atoms get replaced by oxygen from the air. One greenhouse gas is replaced with another.

Living with heat

The White House plan's goal is to reduce fossil fuel use to slow down the atmospheric buildup of greenhouse gases and the projected rate of the Earth's warming. Electricity would come from renewable sources such as wind and solar, cars and trucks would run on electricity, and factories would capture their emissions before they get into the atmosphere. Trains and buses would be more efficient and ubiquitous. New buildings would require less energy to heat and cool.

Economists already see signs that the economy is beginning to shift to the next generation of cleaner, cheaper energy. The price of wind and solar energy has plummeted, and energy-efficient vehicles are increasingly popular.

But because greenhouse gases persist for so long in the atmosphere, scientists warn that reducing emissions will not be enough to protect everyone. Many people will also need help adapting to a hotter Earth.

"Imagine you're driving a train and you're heading right for a cliff," Hsiang says. If you hit the brakes too late, some of the cars will go over the edge.

The train is humanity. The cliff represents deadly heat waves, wildfires, floods and droughts. So far, the U.S. has been tapping the brakes. Now, the U.S. is pledging to press down more firmly and try to stop the train before the whole thing goes over the edge.

But the cliff is looming, Hsiang says. "If we don't slow things down quickly enough, there are large regions of the world, many different people, who will be heavily impacted by the changes that continue to unfold over the next century."

Those most at risk include poor people, people who farm, people who work outdoors and people who live in places that are already dangerously hot or prone to flooding. "Those are the people who get sent off the cliff," Hsiang says.

The Biden administration has acknowledged that reducing U.S. emissions isn't a complete response to climate change. The proposed infrastructure bill would include money to help American towns and cities avoid damage and health impacts from storms, fires and heat waves.

And other countries are also looking to the U.S. for help with adaptation. As a newly reinstated signatory to the Paris climate agreement, the U.S. is back on the hook for $2 billion that the Obama administration pledged to the Green Climate Fund.

The fund exists to help pay for climate-related projects in poorer countries that are already suffering the effects of global warming, including adaptation projects such as building sea walls and transitioning to drought-resistant crops.

Earlier this year, White House climate envoy John Kerry said the U.S. will "make good" on the Obama-era pledge but hasn't said whether it will increase contributions in the future given that it has emitted more cumulative greenhouse gases than any other country.

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The Biden administration is expected to make a big promise next week to dramatically cut America's greenhouse gas emissions over the next 10 years. Scientists say it will take a long time for the atmosphere to show the benefits, but the cuts are crucial if humans hope to avoid the most catastrophic effects of climate change. NPR's Rebecca Hersher reports.

REBECCA HERSHER, BYLINE: Last week, the Earth hit a new record for the concentration of carbon dioxide up in the atmosphere - 420 parts per million. To put that in perspective, humans are now halfway to doubling the amount of CO2 up there, which is why hurricanes and heat waves, wildfires and droughts are all getting more severe.

SOLOMON HSIANG: The reason we have a problem right now is because we are pumping more carbon dioxide into the atmosphere than natural systems can absorb.

HERSHER: Solomon Hsiang is a climate scientist at Berkeley. CO2 and other greenhouse gases come out of tailpipes and smokestacks. They drift up into the air, mixing with oxygen and nitrogen and water vapor. And then they just stay there, trapping heat from the sun.

HSIANG: Greenhouse gases, particularly carbon dioxide, spend a long time in the atmosphere.

HERSHER: Here is the thing about carbon dioxide. It is not a gas that particularly likes playing with other gases. It's pretty stable. So once it's in the atmosphere, it stays in the atmosphere until it's reabsorbed by something down on Earth, like the ocean or a tree or a rock, which can take a long time.

JAMES BUTLER: If you want to get rid of the CO2 in the atmosphere, we're talking thousands of years.

HERSHER: James Butler leads greenhouse gas monitoring for one of the federal government's big atmospheric science labs.

BUTLER: As we start to reduce the CO2 emissions, say, we cut them off, it would still be a lot of CO2 in the atmosphere. And that will continue to warm the planet.

HERSHER: It's not just CO2. Another greenhouse gas, nitrous oxide, takes about a century to break down. Methane, which mostly comes from agriculture and oil and gas wells, is a funny one. It's extremely good at trapping heat, much better than CO2, but it's way less stable, so it breaks down after about 10 years. But when it breaks down, methane can turn into CO2. This is why greenhouse gases accumulate in the atmosphere over time and why, even if the U.S. were to dramatically reduce emissions immediately, it would take a little while for the atmosphere to catch up.

HSIANG: So it's kind of like you're driving a giant train. It's very heavy. You slam on the brakes. The train keeps going for a while, so there is some amount of heating that we would continue to experience.

HERSHER: Hsiang says cutting emissions as much as possible as quickly as possible is absolutely crucial. It will make the world a lot safer for people who are in kindergarten right now. But if humanity is a train that's about to hit its brakes, then it's important to remember that the train is headed for a cliff. And the people who are at the front of this train are those who are most vulnerable to rising seas, more severe heat waves, flooding and droughts.

HSIANG: Those are the people that actually get sent off the cliff, right? They're the ones who really are harmed because we didn't stop the train fast enough. It doesn't mean everyone goes off the cliff. But it does mean, you know, that those people in the front lines - they're going to continue to bear the brunt of climate change for the next several decades.

HERSHER: Around the world, the people on the front lines are more likely to be poor people. It's why cutting greenhouse gas emissions won't be enough on its own. Countries like the U.S. will need to help pay for the costs of adaptation because no matter what, it's going to be a dangerously hot century for a lot of people.

Rebecca Hersher, NPR News. Transcript provided by NPR, Copyright NPR.