Climate change is transforming the character of the West's hottest periods, making them more frequent, more persistent and more deadly.
For almost all of human history, heat waves have been driven by natural variability, or the tendency of weather patterns to occasionally deviate from their typical patterns. Now, however, the buildup of greenhouse gases from the burning of fossil fuels is increasing the likelihood and severity of such extreme heat events.
Although California and the American West will continue to experience cold days and periods of heavy snow cover, scientists say the long-term trend is for the planet to warm further due to the continued burning of fossil fuels. Since 1880, the average global temperature has increased by about 2 degrees.
How is climate change affecting the length and duration of heat waves? How will rising temperatures affect people and ecosystems? How much hotter is it expected to get if current emissions continue unabated?
Here's what the experts say:
How do we know that the planet is warming?
Temperature readings in the Earth's atmosphere and its oceans are monitored by thousands of weather stations, buoys and ships around the world. Scientists use this data to calculate the global average temperature.
“We know the planet is warming because all of these groups are independently documenting a clear, long-term increase in our global average temperature,” said Kristina Dahl, senior climate scientist at the Union of Concerned Scientists, a national nonprofit organization. profit.
“It is a trend that cannot be explained by natural causes, such as changes in volcanic eruptions or solar radiation,” he said. “Human emissions of carbon dioxide and methane, two known and potent heat-trapping gases, explain very clearly the trend we have observed.”
Nineteen of the 20 warmest years on record have occurred since 2000, according to the National Oceanic and Atmospheric Administration.
The year 2023 was the warmest recorded on the planet so far. In July, Phoenix recorded 31 consecutive days of temperatures of 110 degrees or higher, the hottest month on record for any U.S. city.
In 2021, an extreme and anomalous heat wave in the Pacific Northwest killed hundreds of people and approximately one billion sea creatures off the coast of British Columbia. A study of that event found that such heat waves could become 20 times more likely if current carbon emissions continue.
How much hotter is it expected to get if current emissions continue unabated?
Scientists use a variety of possible future emissions scenarios to try to discern how emissions options will affect all aspects of our climate, Dahl said. Here's a sample of what those scenarios show:
- If emissions continue at current levels until about 2050 and then begin to decline, global temperatures would rise nearly 5 degrees by the end of the century. This is what the Intergovernmental Panel on Climate Change considers an “intermediate scenario.”
- With current policies in place, we would experience a similar amount of warming (in the range of 4.3 to 5 degrees) unless those policies are significantly strengthened. California aims to achieve carbon neutrality by 2045, while the nation as a whole aims for 2050. Other countries have longer goals, such as China, which aims for 2060.
- In a worst-case scenario, in which our heat-trapping emissions would triple by around 2075, the planet would warm by about 8 degrees. This is unlikely as it implies higher emissions than the path we are on.
How is climate change affecting the length and duration of heat waves?
Across much of the United States, extreme heat events have been increasing in frequency since the mid-1960s, and the number of high temperature records has exceeded the number of low temperature records since the mid-1980s.
“While there is no single definition of what constitutes a 'heat wave,' we know that cities in the United States and around the world have experienced more intense and longer-lasting heat waves over the past 60 years,” Dahl said. “If we look globally, the number of days with heat waves has almost doubled since the 1980s. During that time, heat waves have also increased in duration.”
What are the possible consequences of rising temperatures for people and ecosystems?
Extreme heat is one of the deadliest effects of climate change. Each year, extreme heat kills more Americans than any other climate-caused hazard, including hurricanes, floods, and wildfires, but it gets much less attention because it kills so silently.
A 2021 Times investigation found that California has chronically underestimated the number of deaths from extreme heat, which disproportionately harms the poor, the elderly and other vulnerable people.
High temperatures can affect the human body in many ways. Heat can cause dehydration, dizziness and headaches, and can worsen underlying health problems such as cardiovascular disease. Health trackers typically show spikes in deaths related to heart problems during and in the days immediately following heat waves.
A scorching heat wave in California in September 2022 killed 395 people, according to state health officials.
During Phoenix's record heat in the summer of 2023, emergency rooms also saw an increase in the number of people suffering from pavement burns, as concrete can reach 170 degrees or more amid high air temperatures . Officials said many burn patients may have passed out on the pavement due to dehydration, poisoning or other factors that prolonged their exposure and complicated their treatment.
People who work outdoors or lack air conditioning are at particular risk of heat-related illnesses and death during an extreme heat event. California has set heat standards for outdoor workers, but has not yet done the same for indoor workers.
Aside from the health risks, “more frequent and severe extreme heat also shapes the way we live and experience the world around us, from whether we can enjoy a visit to a national park to whether it is safe to walk a few blocks.” to get an ice cream cone,” Dahl said.
A Labor Day weekend crowd descends on Huntington Beach as a heat wave hits Southern California, with temperatures in the Valley and inland reaching triple digits on Saturday, September 5, 2020.
(Luis Sinco/Los Angeles Times)
That includes effects on ecosystems.
For example, rising temperatures have allowed pests such as bark beetles to survive over the winter and expand their range, decimating western forests. Avery Hill, a postdoctoral researcher at the California Academy of Sciences, noted that for every additional 1.8 degrees of global warming, up to 40% more trees could die from beetle infestations.
Rising temperatures are also implicated in the drying out of vegetation, which can contribute to larger, faster and more frequent wildfires.
What's more, forests that don't recover from severe fires can shift to completely different ecosystems, which not only affects the variety of plants and animals in the area, but can also affect the broader food web, Dahl said.
It's been hot before. Isn't the planet always changing?
Earth's climate has always changed and will continue to change as a result of things like changes in the shape of our orbit around the sun, Dahl said. However, the changes documented over the past 150 years are unprecedented.
There is more carbon dioxide in our atmosphere now than at any time in the last 2 million years, he said. Sea levels have risen more rapidly over the past century than in any previous century over the past 3,000 years. Glaciers (and the important freshwater they contain) are retreating at a faster rate than at any time in more than 2,000 years.
“The source of these changes is very clear: it is us. “We are changing our climate because of our thirst for fossil fuels and the energy they provide,” Dahl said.
From a geological perspective, one could argue that because humans are part of the planet, these changes are natural, or that we should do nothing to fix our changing climate.
“But the reality is that humans have never experienced this kind of change before,” Dahl said, “and if we want to alleviate the suffering of the people, plants and animals that are experiencing this change most acutely, we will have to stop to do it.” from fossil fuels, and sooner rather than later.”
