A Summer of Sizzle Across the Globe
This summer has seen relentless heat across the Northern Hemisphere. Europe is battling its fourth heatwave of the season, with temperatures soaring above 40°C, sparking wildfires and drying up major rivers like the Danube. Across the Atlantic, a massive
heat dome has settled over large parts of the United States and Canada, putting millions under heat alerts with temperatures in some areas hitting a scorching 46°C. Meanwhile, parts of Asia have also been grappling with extreme heat, continuing a trend of record-breaking summers. This widespread and concurrent nature of extreme heat is no coincidence; studies show that the frequency of simultaneous heatwaves has increased sixfold over the last 40 years. These events are also covering more area and are more intense than in previous decades.
The Culprit: A Wobbly Jet Stream
One of the primary drivers behind this phenomenon is the behaviour of the jet stream, a high-altitude river of air that flows from west to east. Typically, the jet stream's steady flow helps move weather systems along. However, scientists have observed it becoming weaker and wavier. This 'wobble' is linked to the faster warming of the Arctic compared to the rest of the planet, a phenomenon known as Arctic amplification. A wavier jet stream can create large, slow-moving or stationary weather patterns. When a high-pressure system gets stuck, it can lead to prolonged periods of the same weather—in this case, relentless, baking heat.
Life Inside a 'Heat Dome'
The term ‘heat dome’ has become common in weather reports, and for good reason. It’s the mechanism directly responsible for the soaring temperatures. A heat dome occurs when a strong high-pressure system becomes parked over a region for an extended period, acting like a lid on a pot. The high pressure forces air to sink, and as it sinks, it compresses and warms up. This process also prevents clouds from forming, leading to uninterrupted sunshine that further bakes the ground. The trapped hot air is recirculated, getting hotter each day, which is why temperatures can continue to climb for days or even weeks. This summer, these stubborn heat domes have been the cause of record-breaking temperatures in both North America and Europe.
The El Niño Effect and Other Factors
Adding another layer of complexity this year is the development of a potentially strong El Niño. This natural climate pattern involves the warming of ocean surface temperatures in the tropical Pacific, which can shift weather patterns globally. While not the cause of long-term climate change, a strong El Niño can supercharge global temperatures and increase the risk of regional extremes, from heat and drought to heavy rainfall. Forecasters are already seeing the atmospheric fingerprint of this developing El Niño in the current weather patterns over North America and Europe. Additionally, record-warm oceans are pumping more energy into the climate system, while dry soils in many regions mean more of the sun's energy heats the air instead of evaporating moisture.
The Unmistakable Backdrop of Climate Change
While mechanisms like heat domes and the jet stream explain the 'how,' long-term climate change explains the 'why.' A warmer planet provides a higher baseline temperature, so every heatwave starts from a warmer point. Scientific consensus is clear that human-caused greenhouse gas emissions have made heatwaves more frequent, longer, and more intense. Studies show that the probability of experiencing summers with widespread extreme heat, like the one in 2018, is now significantly higher. With every degree of global warming, the area affected by simultaneous heatwaves is projected to grow, making these global-scale heat events a more common and dangerous feature of our summers.
