Dangerous spring heat wave threatens millions in Brazil

An extreme heat wave that's sweeping Brazil is setting daily and monthly records, and causing spring temperatures to soar to levels that would even be unusually hot during mid-summer in some areas.

The big picture: The death of a woman at a Taylor Swift concert at which firefighters said 1,000 fans fainted in searing Rio de Janeiro heat Friday comes as the National Institute of Meteorology warns that Brazilians face "great danger" from this extreme weather event.

• In addition to threatening people's lives, the heat wave has triggered fires and power outages in Sao Paulo and Rio, exacerbated drought in the Amazon and threatened crops and biodiversity elsewhere in Brazil.

Zoom in: The combination of heat and humidity in Rio, a city of 6.7 million, led to perilous heat indices, with feels-like temperatures climbing well into the 100s over the weekend.

• These readings make it hard for the human body to cool itself properly, and increase the risk of heat illness, including heat stroke, which can be fatal.
• According to extreme weather researcher Maximiliano Herrera, one location in Rio recorded a maximum air temperature of 42.6°C (108.7°F). If accurate, this would set a monthly record.
• Herrera noted that in Rio's suburbs, the heat index climbed as high as 58.5°C (137°F), which he said is "arguably the highest/near the highest in South America climatic history" and in all of the Americas.
• "The ongoing heat wave is not limited to Brazil, with Peru and Bolivia also setting record highs," Herrera wrote on X, formerly Twitter.

Context: The extreme heat across much of Brazil, with the greatest temperature departures from average focused in the country's southeast, where Rio is located, is due in part to an area of high pressure aloft.

• This weather feature, also known as a heat dome, promotes sinking, warming air, and deters showers and thunderstorms from forming.

Meanwhile, meteorologist Jeff Berardelli noted that the wet season that usually begins in October was late and that the "dry season was very dry adding to extremes."

• This has helped create favorable conditions for thousands of wildfires that are scorching Brazil's Pantanal wetlands — which are home to 159 mammals, including the jaguar.

Of note: Climate change is raising the odds and severity of heat waves in Brazil and globally, with some heat waves shown to be virtually impossible without human-caused warming.

• El Niño is also likely playing a role in the large-scale weather patterns, leading to some of the heat this winter and spring in South America.

State of play: This extreme weather event follows an earlier spring heat wave that hit South America, when parts of Brazil recorded temperatures of 40°C (104°F).

• A recent climate attribution study found that climate change made that September heat wave much more likely, and 1.4°C (2.52°F) to 4.3°C (7.74°F) hotter, on average, than it would have been in the absence of climate change.
• Last winter was one of the hottest on record in the continent, as temperatures surpassed 40°C (104°F) in parts of Brazil, Argentina, Paraguay and Bolivia.

Go deeper: Earth likely briefly passed critical warming threshold on Friday