What is a heat wave and what causes it to be so hot?


The thermometer in Death Valley shows 130 degrees Fahrenheit (54 degrees Celsius).

Just looking at this makes my mouth water.
photo: Patrick T Fallon/AFP (Getty Images)

We live in an era of infinite heat. Winter or summer, Arctic or tropical, doesn’t matter. Heat waves have become the norm in climate crisis and modern life.

The United States faces record high temperatures in 2021, including now as The hottest everThe national temperature is 4.2 degrees Fahrenheit (2.3 degrees Fahrenheit) higher than normal, and dangerously high temperatures have repeatedly enveloped the West.

This year’s high temperature, let alone the high temperature in the next few years, will have a profound impact. Hundreds died In the Pacific Northwest There are an estimated 1 billion species of marine life In record high temperatures. The reservoir has shrunk. The infrastructure really melted.

The heat wave in the future will only get worse. This makes it more and more important to understand them, from what heat waves are (a surprisingly tricky proposition!), how to predict them further in advance so that people have warnings, and what is about to happen.

What is a heat wave?

Of course, a heat wave means that it has been very hot for a long period of time. But from a meteorological point of view, this does not completely eliminate it. (Seriously, imagine a record book, if The internet has its way.)

“This is a simple question, and surprisingly there is no simple answer,” said Karen McKinnon, a researcher at the University of California, Los Angeles.

Although high temperatures are the number one weather-related killer in the United States, there is no standard definition or threshold for heat waves. Certain temperature markers can trigger high temperature warnings or recommendations from the National Weather Service on any day or even a few days. But when it comes to identifying heat waves, Official vocabulary of the institution Include this definition:

“A period of unusually hot and humid weather. Usually a heat wave lasts for two days or more.”

Compare this with the detailed entry in the glossary of “severe freezing spray”, which reads: “Due to some suitable combination of cold, frozen water droplets on ships accumulate at a speed of 2 cm or more per hour. Water, Wind, cold air temperature and boat movement.” Okay.

McKinnon pointed out that in addition to the temperature being hotter than normal for two days or more, there are other ways to consider what constitutes a heat wave. For researchers, it is helpful to consider which percentile belongs to during periods of extreme heat. This makes it easier to parse the data. Many of the ways we talk about heat waves also focus on day highs, but she pointed out that overnight lows are equally important.

“Especially for human health, it is very important for our body to cool down at night,” she said. “Therefore, for people who are more concerned about human health, the definition of heat waves usually also considers changes in night temperature. One way of thinking is that you may want to define heat waves for the input you are interested in. Therefore, heat waves for human health may be different Due to heat waves affecting crops.”

How did the heat wave form?

Well, it depends on how long you have been. The short answer is that there are many ways. The longer answer is that it depends on how deep you want to go.

High-pressure areas are often the culprit of heat waves, especially in summer. They can lock in a continuously clear sky and increase as heat radiates from the ground, locking in higher pressure. There is even a term: thermal dome. This was the setting that led to the deadly Pacific Northwest heat wave in June 2021. But the local topography can also play a role.

North Carolina climatologist Kathie Dello tweeted DM: “At PNW, due to the easterly wind generated by the clockwise high pressure, the Cascade Mountains helped raise the temperature because the warm air’s downhill ‘Leave the mountain.”

Sometimes the wild zigzag in the rapids also helps to carry heat from low latitudes to colder areas in the north (or south, depending on where you are on the equatorial side). In fact, when the jet stream becomes very wavy, it can actually help researchers predict where the heat wave will form.You can imagine the jet stream like Battle ropes in the gym People use to exercise their arms. When you use these ropes, it can send oscillations along the rope from your swinging arm, and you can control whether they are large or small oscillations.

The same is true for jets. Various disturbances, whether tropical cyclones in the western Pacific or large areas of high pressure elsewhere, can cause rapids to oscillate like gym ropes. These oscillations are set to predictable numbers. This is why you have all kinds of hot spots around the world.For example, during the heat wave in the Pacific Northwest, there were also High temperature in parts of Europe.

“Extreme is not single,” McKinnon said. “They are often in the same place.”

Good news for forecasters, but bad news for disaster managers (or your humble extreme weather reporter), because it means multiple crises must be dealt with at the same time.

Climate change amplifies heat waves

It may not be shocking that climate change (aka global warming) has caused more severe high temperatures. But surprisingly, warming of about 1.8 degrees Fahrenheit (1 degree Celsius) has a huge impact on the frequency and severity of heat waves.

“Our background status is changing,” Dello said. “So when we talk about a few degrees of warming on average, we reach our goal by having more hot days​​. As we continue to add endothermic gases to the atmosphere, we see how sensitive the climate is, and Have unprecedented heat.”

Scientists often invoke the idea that climate change is like Load the dice This makes extreme weather more likely. However, I would like to propose a new analogy. It’s like replacing the dice altogether. Our new dice do not provide 1 to 6 on a six-sided dice, but from 2 to 7, and they are loaded to start. The Northwest heat wave in late June and early July 2021 illustrates this point ingeniously.recent Snapshot analysis It shows that this is a 150,000-year event without climate change. In our current climate, this is an event that occurred in 1,500 years, which makes the almost unimaginable now a fringe event. If the world somehow manages to keep the temperature within the 2 degrees Celsius (3.6 degrees Fahrenheit) threshold set by the Paris Agreement, then this event will likely occur every 5 to 10 years. It’s puzzling to think about it.

“Climate change is causing us to obliterate our high temperature records, and if we don’t take action on the climate, these will be cool summers in the 21st century,” Dello said.

We urgently need to adapt to the high temperature environment

Considering the risks that have occurred from the unprecedented fires in Australia and Siberia last year to the Arctic sea ice erosion in the northwest and elsewhere, it is clear that our work is done. First, reducing emissions is crucial.

But the same is true for adapting to heat waves. There are some success stories worth seeing, even though they all happened after tragedies. In 2003, a heat wave An estimated 70,000 people died in Europe.Governments respond More user-friendly warning system and other calorie plansIn subsequent years, more severe heat waves caused fewer deaths.

The Northwest Territories are still counting deaths, but it is becoming clear that many people are poor, old and/or alone at the time of death. More cooling centers or programs that provide air-conditioning subsidies to those in need are one way to help. Low-income families, especially black, Latino, and Aboriginal families, Spend four times Like its wealthier counterparts, in public utilities. Obviously, the playing field needs to be leveled. Social projects can also play a role.New York recently implemented a Pilot project “Promote community cohesion” by ensuring that those who are staying at home are inspected under extreme heat.Mutual aid groups Played a key role To deal with the high temperatures in the Pacific Northwest.

But individual-level repairs are not enough. Our city needs to overhaul the heat. This includes more green space to combat heat islands, especially in poorer communities and communities of color. For example, the red line community, Facing more extreme heatGiven the energy burden that black and brown communities endure under extreme heat, any plan to help people stay cool is more important than ever.



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