Pima County, Arizona (CNN) — At least 147 people have died in just five counties in the U.S. heatwave, coroners have reported — just a snapshot of the death toll this scorching summer has brought. . And experts say this estimate is likely to be far lower than the actual number of lives lost in the extreme heat.

The deaths reported here occurred in three states that endured the worst heat this summer. As of early August, 64 people had died in Pima County, Arizona. 39 in Maricopa County, Arizona. 26 Clark County, Nevada. 11th in Webb County, Texas. and seven in Harris County, Texas.

Some parts of California, the South and Midwest, also reported some heatstroke deaths, but the death tolls were not as high as in the five counties reported here. Maricopa County, home of Phoenix, officially counts at least 39 heat-related deaths.Another 312 deaths still under investigation of possible heat-related causes of death.

The death toll comes as temperatures rose to record levels at the end of June and continued to rise across much of the South and Southwest through July. Most notably, Phoenix just recorded the hottest month of any U.S. city, with temperatures above 110 degrees Fahrenheit for 31 consecutive days from June to July.

The number of deaths due to heat waves so far is tornadoand floodCombined. Scientists warn that heatwaves will get worse with the climate crisis, but many regions still do not report heat-related deaths accurately or regularly.

Harvard physician and historian David S. Jones said the figures reported here, and those more widely reported across the country, are likely to be underestimated. He called the Earl “mysterious”.

“The low number of reported deaths is really baffling,” Jones told CNN. “Hundreds of people have died in the past from less severe heatwaves in the United States. I think so, but there is no proof of that.”

Jones said the death toll may be lower in the south because people are acclimatized to the heat and generally have more access to air conditioning.

But he stressed that reporting on the cause of a person’s death is always a “complex process.” A coroner or coroner must give a single cause of death, but in some places those officials may be politically appointed or elected officials with no medical background.

“The[cause of death]assessment itself is complex,” Jones added. “When someone is found dead in an apartment and you try to find out what the leading cause of death was, many medical examiners will say, ‘The person died of some kind of heart disease. It must be.’ My heart stopped.”

Epidemiologists say extreme heat doubles risk and could be a major factor in most cases where it’s unclear whether heat ultimately led to death.a 2020 Surveyfound that heat-related deaths were underestimated in 297 of the country’s most populous counties. The researchers said death records tend to ignore other possible heat-related causes of death, such as heart attacks.

The Centers for Disease Control and Prevention estimates heat-related mortality based on death certificates listing heat as the primary or contributing cause of death. About 700 people die each year from heat, according to the CDC.

But the National Weather Service estimates that only 148 people died from heatstroke last year, with a 10-year average of 153 and a 30-year average of 168.

Both heat stroke deaths in the United States suggest far fewer people are dying from heat stroke than in European countries, where last summer’s scorching heat wave killed about 62,000 people.

Jones said there are several explanations for why US statistics appear to be inconsistent. It could be that the US is underreporting the numbers, or the heat could be more lethal in Europe because there is no air conditioning, or it could be a combination of the two.

“The United States has long struggled with getting comprehensive health data quickly,” he said. “Cities report states, and states report to the CDC, but it happens at varying rates and with varying degrees of accuracy. And we have a robust system of comprehensive and rapid health data. not.”

The numbers show how extreme heat can pose serious health risks. Heat kills more Americans in the United States than any other weather disaster. The climate crisis is making these extremes even deadlier, and this summer’s unusually hot weather is proof of just that.