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.”

Perhaps never before have so many been so eager for something so steeped in heartbreak.

Taylor Swift‘s legions of devotees have eagerly anticipated her new album, “The Tortured Poets Department,” in hopes of gaining insight into her notoriously private six-year relationship with actor Joe Alwyn — particularly her perspective on its demise.

Swift delivers. In a track titled “Fresh Out the Slammer,” the 14-time Grammy Award winner sings of spending “Years of labor, locks and ceilings / In the shade of how he was feeling.” Another song called “So Long London” has her recounting that “I stopped CPR, after all it’s no use / Thе spirit was gone, we would never come to.”

“Songwriting is something that, like, actually gets me through my life, and I’ve never had an album where I needed songwriting more than I needed it on ‘Tortured Poets,’” Swift confessed to an audience in Melbourne, Australia, when her Eras tour played there in February.

Embracing a breakup album may seem like a macabre thing to do. But psychologists and cognitive scientists say songs about relationships gone bad actually can do listeners a lot of good.

“When people have a romantic breakup, they feel very alone in their experience,” said David Sbarra, a professor of psychology at the University of Arizona who studies how marital separation and divorce affect health. “They feel very isolated and think that the unique individual circumstances that characterized their breakup are particularly terrible.”

A breakup song can change that, said Sbarra, who conducted a deep dive into the emotional authenticity of Olivia Rodrigo‘s lyrics about a doomed relationship on her debut album “Sour.”

“Songs play a powerful role in normalizing our experience, in making us feel that we are not this weird, unusual, distorted kind of person,” he said.

Indeed, almost everyone who has reached their late teens has lived through the demise of a romantic relationship and endured the gamut of emotions that accompany it.

“The songs function to affirm their emotions, validate them, remind the listener they are not alone,” said Bill Thompson, a psychologist at Bond University in Queensland, Australia, who studies why music is important to people. “The emotions associated with breaking up are universal. They are a natural part of being human — even if they are also painful.”

Thompson said the concept of a love song — and by extension, a breakup song — may be written into our genes. Birds are known to serenade potential mates, while mice, humpback whales and other species use vocalizations to attract their partners.

“So among our ancestors, music might have played a role in mate selection and courtship,” he said. “It’s possible the prevalence of songs about love and courtship is a remnant of this ancestral function.”

The Sumerians of Mesopotamia devised a love song by around 2000 BCE, and scholars of Ancient Egypt have found love songs inscribed into pottery and written on sheets of papyrus. But it’s not clear when the first breakup song arose.

Why breakup songs caught on is less of a mystery, experts said.

“Breakups certainly inspire a rich broth of emotions,” said Arianna Galligher, a licensed clinical social worker and director of the Stress, Trauma and Resilience program at The Ohio State University Wexner Medical Center. “For a lot of people, listening to music helps them sort through their own emotional experience.”

Sadness is often the primary emotion in a breakup song. But it’s certainly not the only one.

The 10-minute version of Swift’s “All Too Well” evokes a range of strong feelings, including “sadness at the end of the relationship, nostalgia about the past romance, regret that the relationship failed, anger at being dumped, resentment that the boyfriend moved on to other young women, scorn at his unfaithfulness, and fear of being hurt again,” Paul Thagard, a philosopher and cognitive scientist at the University of Waterloo, writes in his forthcoming book “Dreams, Jokes, and Songs.”

“I think it is a fabulous song,” Thagard said in an interview. “The reason it’s such a fabulous song is that it manages to convey a lot of different emotions.”

There’s no rule that says the emotions in a breakup song have to be negative. If a relationship was a poor fit — or even toxic — it’s appropriate to celebrate when it comes to an end, Galligher said.

Likewise, a breakup song suffused with sadness can resonate with a listener in a rock-solid relationship who is coping with another kind of loss.

“Sadness is not exclusive to breakups,” Galligher said. “Sometimes it can be helpful to listen to a song that is ostensibly about a breakup, but it helps you tap into something inside of you that knows sadness.”

She recalled a time that Adele’s “Someone Like You” came on the radio as she was driving to a memorial service.

“I was in a perfectly functional relationship, very happily coupled, and I found myself tapping into the song’s sadness and grief related to the loss of my friend,” she said. “It was really helpful to be able to access those emotions.”

When a breakup is fresh and the pain is raw, a song can serve as “a virtual empathetic friend” by affirming and validating a listener’s emotions, helping them process their feelings, and reminding them they’re not alone, Thompson said.

“The advantage is that you won’t get unwanted advice,” he said. “Music is just there for you and supportive.”

Thagard agreed: “There’s no judgment coming from a song.” (Unless you’re one of the unlucky men who has broken Swift’s heart.)

In addition, binging on breakup songs can be part of “a habituation process” that reduces the intensity of feelings associated with a romantic split, Sbarra said. Some people may find that necessary before they’re ready to talk about their breakup with another person.

“Sometimes folks need to spend a little time reflecting on their own feelings,” Galligher said. “Having a little bit of solitude to be introspective can be really beneficial, and then you seek the connection with others.”

Yet for all that breakup songs have to offer, it’s still possible to have too much of a good thing. Studies have found that listening to sad music can make sad people feel even sadder by prompting them them to dwell on their sadness.

“You do have to take your temperature about whether this is ultimately helping you or hurting you,” Sbarra said.

That said, listening to breakup songs can be a healthy way of distancing oneself from a painful event.

“It’s not you,” he said. “It’s Taylor Swift.”

American life expectancy started dropping even before the pandemic. It’s a critical barometer of our nation’s health and a sign that all is not well in the U.S.

Much of the increase in preventable, premature death is attributable to drug overdose, which increased five-fold over the last couple decades. But this malaise is far broader, driven largely by growing chronic illness.

Rates of depression are reaching new highs. Obesity rates among adults have risen from 30% to 42% since the turn of the century, with severe obesity nearly doubling and driving up the risk of cardiovascular disease, diabetes and other serious health conditions. The return of vaccine-preventable illnesses has been a concern since the 2010s. Sexually transmitted infections have surged in the last decade. And for the first time since 1937, an infectious disease, COVID-19, became one of the top three causes of death in the country.

These health problems are alarming on their own. They also have a devastating impact on our economy. A one-year increase in life expectancy could boost economic output by 4%. On the other hand, as Americans’ health declines, our health expenditures continue to soar. As a country, we spend $4.5 trillion annually on health, representing 17% of GDP. Out-of-pocket healthcare costs have risen dramatically, straining workers’ finances and pushing people into bankruptcy. All this fuels a cycle of a sicker workforce and a weaker economy.

Policymakers acknowledged the link between the economy and public health at the height of the pandemic, providing federal relief programs such as cash assistance and paid sick leave designed to keep the nation’s workforce and economy as healthy as possible. But our abandonment of these efforts since getting COVID relatively under control sets our country up for mounting crises. We need to revive a historical source of support for public health measures: the business case for a healthy workforce.

In 1842, Edwin Chadwick argued in his landmark “Report on the Sanitary Conditions of the Labouring Population of Great Britian” that public health investments are crucial not only from a moral perspective, but also for economic productivity. Writing for the Atlantic in 1909, C.-E. A. Winslow, an American public health pioneer, wrote that employers who try welfare measures for workers “find that it pays.” And around that time, Wickliffe Rose, an American philanthropist, oversaw the Rockefeller Sanitary Commission to tackle hookworm disease as a controllable health problem, spurring economic productivity.

Hookworm, which can cause anemia and fatigue and impair development in children, was a significant problem in southern states in the late 1800s and early 1900s resulting from lack of access to clean water, poor sanitation and poor hygiene. Its symptoms were blamed on “laziness” — a stigma often attached today to symptoms of chronic illnesses, disabilities and mental health issues — and perpetuated cycles of poverty. Rose all-but-eradicated hookworm through education campaigns, expanding access to treatment and improving public sanitation.

Similarly, during World War II, the U.S. government invested in public health initiatives to curb the transmission of malaria in tropical and subtropical battlefronts; vaccinate against smallpox, typhoid fever and tetanus; and control sexually transmitted infections, which during World War I cost the U.S. Army more than 7 million workdays and 10,000 preventable discharges.

When it functions well, such public health infrastructure makes it easier for working people to lead healthy lives. The results have been dramatic, contributing in the last century to the average human lifespan doubling around the world.

Despite the impression given by COVID-19, public health has historically been about so much more than tracking disease outbreaks. It’s been about preventing disease. Access to healthcare and insurance play a role, but doctors and hospitals most often come into play after someone is already sick. Research shows that simple resources such as clean air and water, affordable healthy food, stable housing and safe workplaces are much better predictors of good health and longevity.

During the pandemic, programs addressing basic needs — eviction freezes, expanded food assistance and mandated paid sick and family leave for employees in smaller companies — enhanced housing stability, curbed COVID spread and protected Americans’ mental health. Since then, home affordability has plummeted; half of American renters spend more than 30% of their income on rent and utilities. In 2022, more than 40 million Americans lived in food-insecure households, adding to health issues in adults and children.

The U.S. is one of the only high-income nations that still lacks universal paid sick leave and family medical leave, forcing many people to go to work sick or risk losing a day’s wages. Interventions to improve workplace air quality, a vital component of a healthy workplace appreciated even by 19th and 20th century health reformers, have been overlooked.

The pandemic-era measures were dropped in part because of their cost. But what is much more expensive, and what is causing American workers needless suffering as our national health declines, is our current approach to health. Of our $4.5-trillion annual health spending in the U.S., the vast majority goes to treating people when they are already sick; only 4% supports programs to keep people and workers healthy in the first place. This focus on treating individuals after they have already fallen ill is much of the reason we pay dramatically more than other countries yet still have some of the worst health indicators in the world.

Once again treating public health as an economic imperative could help broaden support for the type of interventions that became polarizing during the pandemic — but have a long track record of improving wellbeing and productivity.

Céline Gounder (@CelineGounder), an infectious-disease physician and epidemiologist, is the senior fellow and editor-at-large for public health at KFF Health News. She is also the host of the podcast “Epidemic.” Craig Spencer (@Craig_A_Spencer) is an emergency medicine physician and professor of public health at Brown University.