Why is summer unusually hotter this year?

Despite the fact that summer has only been here for a few weeks, a record-breaking increase in heatwaves has people longing for cooler weather. A sharp increase in mortality rates as a result of the extreme heat is another effect of this unusually hot weather.

A scorching heatwave is currently affecting parts of Texas and the southwest of the US. The US National Weather Service reported that at one point, more than 120 million Americans were subject to some kind of heat advisory, which equates to more than one-third of the entire population.

The heat in June shattered all-time records in the UK. The previous record, set in 1940, had been surpassed by a significant margin of 0.9°C.

The Middle East, North Africa, and Asia have all experienced unusually hot weather. It comes as no surprise, then, that June was the hottest month on record, according to the European Centre for Medium-Range Weather Forecasts.

Nevertheless, the temperature has not even begun to drop.

According to the EU Copernicus climate and weather service, the three hottest days ever recorded occurred in the previous week. On Monday, July 3, the average global temperature reached 16.89°C, and on Tuesday, July 4, it surpassed 17 °C for the first time, averaging 17.04°C.

Preliminary statistics suggest that the recent temperature on July 4 was surpassed on July 5, when temperatures climbed to 17.05°C.

"These highs are in line with what climate models predicted," says Prof Richard Betts, climate scientist at the Met Office and the University of Exeter. 

"We should not be at all surprised with the high global temperatures," he says. "This is all a stark reminder of what we've known for a long time, and we will see ever more extremes until we stop building up more greenhouse gases in the atmosphere."

In addition, the majority of Earth's heat is stored near the surface, not in the atmosphere but in the oceans. 

Record ocean temperatures have been observed this spring and summer, with the North Atlantic experiencing the highest surface water temperatures ever recorded. The UK coasts have experienced temperatures as high as 5 °C above normal, CNN reported.

The US National Oceanic and Atmospheric Administration (NOAA) has labelled the current heatwave a Category 4 heatwave, a designation rarely used outside of the tropics that denotes "extreme" heat.

"Such anomalous temperatures in this part of the North Atlantic are unheard of," says Daniela Schmidt, a professor of Earth Sciences at the University of Bristol.

Simultaneously, El Niño develops in the tropical Pacific, a recurring weather pattern caused by warm waters rising off South America. It is perhaps not surprising that Atlantic and Pacific heatwaves led to record-breaking high sea surface temperatures in April and May, dating back to 1850.

"If the seas are warmer than usual, you can expect higher air temperatures too," says Tim Lenton, professor of climate change at Exeter University.

"Most of the extra heat trapped by the buildup of greenhouse gases has gone into warming the surface ocean," he explains. "That extra heat tends to get mixed downwards towards the deeper ocean, but movements in ocean currents, like El Niño, can bring it back to the surface."

"When that happens, a lot of that heat gets released into the atmosphere," says Prof Lenton, "driving up air temperatures."

Moreover, climate change causes record-breaking temperatures, increasing greenhouse gas emissions, and energy-related CO2 emissions, with growth slowing slightly but still up almost 1% last year, according to the International Energy Agency.

El Niño is predicted to make 2023 the world's hottest year, potentially pushing the world past the 1.5°C warming milestone. 

Without drastic emissions reductions, temperatures will continue to rise, with record June temperatures having doubled due to man-made climate change. This is driving irreversible ecosystem changes, including marine heatwaves.

The world is racing towards a hotter, more chaotic climate future, but the challenge is to reduce emissions rapidly enough to slow the climate juggernaut and manage global warming's impacts.