Although it is still spring in the Southern Hemisphere, temperatures have risen well above what is typical even in summer, which is more than a month away.
A stagnant area of high pressure, El Niño and anthropogenic climate change have converged to generate this excessive heat.
Rio has seen a stifling combination of heat and humidity for days. On Friday, when the woman died at the concert, midday temperatures reached 100 and dew points, a measure of humidity, were in the upper 70s. Any dew point above 75 degrees is oppressively humid.
At a dew point of 77, about 23 grams of water, or about 1.55 tablespoons, is present in each cubic meter of atmosphere. It is the weight of about nine pennies.
The heat index on Friday — a measure of how it feels in terms of humidity — topped 120 degrees. Climate historian Maximiliano Herrera tweeted the heat index reached as high as 137 degrees in Rio’s suburbs on Saturday.
The higher the heat index, the less sweat can evaporate from our bodies. This is because the air is already closer to its moisture storage capacity. At high heat indices, less heat can evaporate from our skin and cool us down as a result. This can lead to difficulties in regulating our body temperatures. If left unchecked, heat exhaustion and heatstroke can occur.
Saturday’s temperatures around Rio were both dangerously high and record-setting. Rio’s Jacarepaguá-Roberto Marinho Airport reported a heat index of 131 degrees Saturday morning, the product of a temperature approaching 97 degrees and a dew point of 86. Most of the city’s other airports saw highs between 105 and 107 degrees.
According to Herrera, the town of Seropédica, a suburb about 25 miles west-northwest of Rio and 15 miles inland, hit 108.7 degrees, a record in November.
Record high temperatures also spread to Peru and Bolivia. On Saturday, highs of 102.6 degrees in Tingo de Ponaza, Peru and 102.2 degrees in Cobija, Bolivia set November records, according to Herrera.
The heat first moved into Brazil about a week ago. The BBC reported that red alerts were issued for almost 3,000 cities due to “unbearable” heat. On November 12, it said, Rio hit 108.5 degrees, a record for the month.
The intensity of the heat is expected to ease somewhat after Sunday, but temperatures are expected to remain warmer than normal through the next week in central South America.
What drives the heat
Contributing to the warmth has been a counter-clockwise surface high pressure system just off the coast of Brazil. It’s induced warm, humid northerly winds that pump in the same kind of moisture characteristic of the Amazon rainforest. There is also a “heat dome” or ridge of warm, sinking air at higher elevations. While it deflects the jet stream and all bad weather and cloud cover away, it promotes warm sunshine.
The heat is also being boosted by a strengthening El Niño, the climate pattern associated with warmer-than-normal ocean waters in the tropical Pacific.
Furthermore, the frequency, intensity and duration of extreme heat events, such as this one, are increasing due to anthropogenic climate change. The planet has just observed its warmest 12-month period on record, and the last five months have all been the warmest on record.
According to the UN, Brazil has warmed by 0.9 degrees over the last few decades. Changes in land use, including deforestation of the Amazon, are expected to accelerate this pace of warming.
