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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.
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