An onslaught of record-breaking heat across much of the US has provided yet another indicator of a longer-term issue – summers are progressively getting hotter for Americans in all corners of the country.
The US climate scientist Brian Brettschneider has analysed almost 130 years of federal data and it shows that from New York to Los Angeles there are hotspots where summers have got significantly hotter in that time compared with the average levels of warming brought about by the burning of fossil fuels.
Summers are, on average, now about 0.8C (1.5F) hotter across the US than this earlier period, but many places have had far more extreme summertime increases, being up to 2.8C (5F) hotter.
More than a third of people in the US live in a county that has summers 1.5C (2.7F) hotter, or more, than they were on average in 1895, Brettschneider’s analysis of federal government data shows. This means that about 117 million Americans are experiencing these new conditions, with 55.7 million of these people in counties that have heated up by 2C (3.6F) or more.
A smaller, but significant, number of people, about 12 million, live in places that have heated up 2.5C (4.5F) or more over summer since the 19th century. Globally, the average year-round temperature is slightly more than 1C (1.8F) warmer than it was in pre-industrial times, with last year the hottest ever recorded, the latest in a string of record annual highs.
“Summer is a time is when we are hyper-aware of warm temperatures and many of us are feeling that right now,” said Brettschneider, a climate scientist who compiled the county-level figures drawn from National Oceanic and Atmospheric Administration (Noaa) temperature data for the summer months stretching back to 1895.
The fastest-warming counties span places with sparsely populated desert, rugged mountains and breezy coastal cities, with the three highest temperature increases over summer occurring in Grand county, Utah; Ouray county, Colorado; and Ventura county, California. The counties that include Los Angeles, Baltimore and Phoenix all have summers 2.2C (4F) or more hotter than the prior average, while the heart of New York City is 2.1C (3.8F) warmer.
Regional temperature discrepancies are influenced by factors such as natural variation and land-use changes, as well as the overall warming climate, cautioned Jane Baldwin, a climate scientist at the University of California, Irvine.
Winters are warming more quickly than summers, too. But even seemingly small increases in summer temperatures can have an outsized impact in fueling punishing heat, Baldwin said.
“One degree celsius of warming may sound relatively small but it can translate into quite substantial impacts as it’s an average and the extremes of that average can cause much higher likelihoods of deaths from heatwaves, as well as agricultural impacts and wildfires,” she said.
“Heat is a silent killer and it unfortunately affects the most underserved members of society the worst.”
The dangers of warming summers have already been illustrated this year, with record temperatures baking the US south-west and, more recently, the eastern half of the country.
Prolonged heat of 32C (90F) and more has hit about 80% of the population, lingering in some places for the longest time in decades, the National Weather Service has said, adding that the “early arrival of this magnitude of heat, the duration, abundant sunshine and lack of relief overnight will increase the danger of this heat wave beyond what the exact temperature values would suggest”.
The recent heatwave that engulfed much of the southern US, as well as large parts of Mexico and Central America, was made 35 times more likely due to human-induced climate change, according to a rapid analysis by scientists.
Studies have found that summers are generally getting hotter, including much warmer night-times which reduces the amount of relief people get from the elevated temperatures. Heatwaves are getting fiercer and are moving more slowly as the planet warms, with heat now the largest weather-related cause of death in the US.
“We are now starting to have this complicated relationship with summer,” said Deepti Singh, a climate and extreme events expert at Washington State University. “The extreme events are happening more quickly than the rate of mean temperature warming, which is putting a strain on everything we depend upon as a society.
“If you talk to climate scientists, there’s certainly an anxiety as summer approaches. It can be distressing.”
The county-level map of summer temperature increases shows that the warming isn’t uniform, however, with large jumps in heat across much of the US west and in the north-eastern US.
Summer temperatures have somewhat flatlined in the US south-east, meanwhile, a phenomenon known as a “warming hole” that could be down to reflective particulate pollution or reforestation in the region that has helped ameliorate the overall temperature rise, although much of the south-east still gets extremely hot in summer.
Hotter summers not only mean worsening heatwaves – they also contribute to warmer rivers and streams, affecting wildlife, and increase the risk of giant wildfires. More than 50,000 people died because of smoke from various California wildfires in the decade to 2018, a study released this month found, with worsening smoke starting to erase broader progress made in cutting air pollution in the US over the past 50 years.
“People underestimate how at risk they are from the heat,” said Kristie Ebi, an epidemiologist who specializes in climate change impacts at the University of Washington.
“It’s pregnant women, outdoor workers, people on certain medications – the list of vulnerable people is actually quite long. Humans are pretty darn good at thinking others at risk but that they aren’t. We need to understand we are all at risk from this.”
Ebi said there was also a “misconception” that people already living in hot areas can simply acclimatize to extra heat, warning that everyone should check on neighbors, and seek shade, water and cooling when temperatures climb. “There are physiological limits that we all face,” she said.
Longer-term, the hotter summers will keep coming as long as humans continue to expel planet-heating emissions, scientists caution. “Until we stop burning coal, oil and natural gas, conditions like this week’s dangerous heat will become more and more common,” said Andrew Pershing, vice-president of science at Climate Central.
