Summer 2024 was officially the Northern Hemisphere’s hottest on record. In the United States, fierce heat waves seemed to hit somewhere almost every day.

Phoenix reached 100 degrees for more than 100 days straight. The 2024 Olympic Games started in the midst of a long-running heat wave in Europe that included the three hottest days on record globally, July 21-23. August was Earth’s hottest month in the National Oceanic and Atmospheric Administration’s 175-year record.

Overall, the global average temperature was 2.74 degrees Fahrenheit (1.52 degrees Celsius) above the 20th-century average.

That might seem small, but temperature increases associated with human-induced climate change do not manifest as small, even increases everywhere on the planet. Rather, they result in more frequent and severe episodes of heat waves, as the world saw in 2024.

The most severe and persistent heat waves are often associated with an atmospheric pattern called a heat dome. As an atmospheric scientist, I study weather patterns and the changing climate. Here’s how heat domes, the jet stream and climate change influence summer heat waves and the record-hot summer of 2024.

What the jet stream has to do with heat domes

If you listened to weather forecasts during the summer of 2024, you probably heard the term “heat dome” a lot.

A heat dome is a persistent high-pressure system over a large area. A high-pressure system is created by sinking air. As air sinks, it warms up, decreasing relative humidity and leaving sunny weather. The high pressure also serves as a lid that keeps hot air on the surface from rising and dissipating. The resulting heat dome can persist for days or even weeks.

The longer a heat dome lingers, the more heat will build up, creating sweltering conditions for the people on the ground.

How long these heat domes stick around has a lot to do with the jet stream.

The jet stream is a narrow band of strong winds in the upper atmosphere, about 30,000 feet above sea level. It moves from west to east due to the Earth’s rotation. The strong winds are a result of the sharp temperature difference where the warm tropical air meets the cold polar air from the north in the mid-latitudes.

The jet stream does not flow along a straight path. Rather, it meanders to the north and south in a wavy pattern. These giant meanders are known as the Rossby waves, and they have a major influence on weather.

Where the jet stream arcs northward, forming a ridge, it creates a high-pressure system south of the wave. Where the jet stream dips southward, forming a trough, it creates a low-pressure system north of the jet stream. A low-pressure system contains rising air in the center, which cools and tends to generate precipitation and storms.

Most of our weather is modulated by the position and characteristics of the jet stream.

How climate change affects the jet stream

The jet stream, or any wind, is the result of differences in surface temperature.

In simple terms, warm air rises, creating low pressure, and cold air sinks, creating high pressure. Wind is the movement of the air from high to low pressure. Greater differences in temperature produce stronger winds.

For the Earth as a whole, warm air rises near the equator, and cold air sinks near the poles. The temperature difference between the equator and the pole determines the strength of the jet stream in each hemisphere.

However, that temperature difference has been changing, particularly in the Northern Hemisphere. The Arctic region has been warming about three times faster than the global average. This phenomenon, known as Arctic amplification, is largely caused by the melting of Arctic sea ice, which allows the exposed dark water to absorb more of the Sun’s radiation and heat up faster.

Because the Arctic is warming faster than the tropics, the temperature difference between the two regions is lessened. And that slows the jet stream.

As the jet stream slows, it tends to meander more, causing bigger waves. The bigger waves create larger high-pressure systems. These can often be blocked by the deep low-pressure systems on both sides, causing the high-pressure system to sit over a large area for a long period of time.

Typically, waves in the jet stream pass through the continental United States in around three to five days. When blocking occurs, however, the high-pressure system could stagnate for days to weeks. This allows the heat to build up underneath, leading to blistering heat waves.

Since the jet stream circles around the globe, stagnating waves could occur in multiple places, leading to simultaneous heat waves at the mid-latitude around the world. That happened in 2024, with long-lasting heat waves in Europe, North America, Central Asia and China.

Jet stream behavior affects winter, too

The same meandering behavior of the jet stream also plays a role in extreme winter weather. That includes the southward intrusion of frigid polar air from the polar vortex and conditions for severe winter storms.

Many of these atmospheric changes, driven by human-caused global warming, have significant impacts on people’s health, property and ecosystems around the world.

Shuang-Ye Wu, Professor of Geology and Environmental Geosciences, University of Dayton

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Even though preventive care is supposed to be free by law for millions of Americans thanks to the Affordable Care Act, many don’t receive recommended preventive services, especially racial and ethnic minorities and other at-risk patient groups.

The Affordable Care Act exempted preventive services from patient cost-sharing for large chunks of the population. This means that if you receive preventive screening and have private insurance, including through the ACA Marketplace, there should be no copay at time of service, and you shouldn’t get a bill later on. Easy enough, right?

Wrong. Our team of health economists has shown that patients spend millions of dollars every year on unexpected bills for preventive care. The main reason for this is that no specific regulations were put in place to determine exactly which services should be exempted, or for whom, or how often. This omission has left many people on the hook to pay for valuable health care they thought would be free.

Now, in our recently published research in the journal JAMA Network Open, we’ve found that the burden of paying for what should be free preventive care disproportionately falls on some patient groups.

Inequitable claim denials

Looking at data from over 1.5 million patients, our study demonstrates that insurers deny preventive claims for patients from marginalized communities at higher rates than for those from majority groups.

For example, low-income patients were 43% more likely than high-income patients to have their claims denied. In addition, Asian, Hispanic and non-Hispanic Black patients were each roughly twice as likely as non-Hispanic white patients to have claims denied.

Not only were these patients denied routine benefits, but they also saw large differences in rates of billing errors. For example, patients with a high school diploma or less experienced denials due to this kind of billing error almost twice as often than patients with college degrees. All of these services should have been covered by an insurer.

Research on preventive care access is commonly based only on claims data, which doesn’t typically have information on patient demographics. This lack limits a study’s ability to detect differences across patient groups. Our study, however, uses a combination of linked claims data, remittance data containing information on why claims were denied and whether they were resubmitted, and demographic data from self-reports, purchase transactions and voter registries. Together, this richer dataset allowed us to examine differences in denials based on race and ethnicity, education and income, including reasons why patients were denied care.

Preventive care is essential

Equitable access to preventive health care is about more than just physicals, although those are important, too. Preventive health care includes key screenings for cancers, cardiovascular disease and diabetes, access to contraceptives, and mental health checkups, among other services. Ensuring that insurers provide equal coverage for these services for all patients is important to improve health outcomes and quality of life for everyone while reducing future health care costs.

Our results paint a picture of the kinds of hurdles patients face when they seek health screenings. Patients from underrepresented groups were not only more likely to be told their care wouldn’t be covered. They were also more likely to have their claims processed incorrectly, leading to more frequent denials and, ultimately, larger medical bills.

Unexpected bills can affect both a patient’s current health and their future use of health care services. These hurdles can exacerbate an already tenuous trust in a fragmented health care system, making patients less likely to return for follow-up screenings.

Stacked coverage denials for patients who live with multiple marginalized identities or who are less able to advocate for themselves can further entrench racial and socioeconomic inequities.

Ensuring equitable access

Our study paints a compelling picture of where different patients may face hurdles for getting preventive care, but more research is necessary to identify how to ensure equitable access.

As our study looked only at preventive services, we will also need to see how our findings generalize to other forms of health care. More research is also needed to understand how other vulnerable patient groups, such as LGBTQ+ patients or patients with multiple chronic conditions, fare when trying to access care.

Our team is currently studying how actual bills for care differ across patient groups and how patients respond when bills arrive. In our study, more than two-thirds of denied claims were never resubmitted to insurers, meaning that many billing errors go uncorrected at patients’ expense.

Equitable policy on multiple fronts can help rectify the way preventive care is inconsistently and inequitably provided. These include uniform coverage of preventive care by insurers, standardized billing practices for physicians and improved means for patients to advocate for themselves. This can help ensure that everyone has appropriate access to lifesaving health care.

Alex Hoagland, Assistant Professor of Health Economics, University of Toronto and Michal Horný, Assistant Professor of Health Policy and Management, UMass Amherst

This article is republished from The Conversation under a Creative Commons license. Read the original article.