Gwynne Dyer
First the ‘heat dome', with temperatures in the mid-to-high forties Celsius in many parts of western North America for up to a week (49.6° C in Lytton, B.C.). Then, when the forests were tinder-dry, came the wildfires (which wiped Lytton out). From northern California to northern BC, the records were being broken every day. The extreme temperatures were unprecedented, but the weathermen had an explanation of sorts: a ‘heat dome' that trapped hot air in the same area for a long time while the heat kept rising. Many meteorologists know that this could be our first glimpse of a new normal in which killer heat waves become regular events. The proposed name for these new, lengthy super-hot spells is ‘wave-7' or ‘wave-5' events because the heat waves strike simultaneously in several large regions around the planet. ‘Wave-7”, the likelier candidate in this case, hits western North America, western or central Europe, and western Asia all at the same time. Wave-7 is still a hypothesis, not a proven fact, but we had just that pattern of extreme heat in late June. The temperatures were in the mid-to-high 40°C in western Canada and the US Pacific northwest for four consecutive days. Temperatures were hitting 35-40°C in central Europe and the Balkans. In western Asia, the heat reached the mid-40s in most of Pakistan and the high 30s all over Siberia, with peaks of 48°C in Jacobabad and Verkhoyansk. (The latter is on the Arctic Circle). It may all be connected to the jet stream, a high-altitude, high-speed ‘river' of air blowing from west to east around the planet. It used to flow so fast and straight that eastbound airliners cut an hour off their eastbound trans-Atlantic and trans-Pacific flights by hitching a ride on it. But they don't do that so much now, because the jet stream has slowed down and wanders all over the place. It has slowed because it gets its energy from the temperature difference between the Arctic air mass and the much warmer air of the temperate zone. The jet stream is the boundary between the two. But the Arctic is warming twice as fast as the rest of the planet, so the difference in temperature — and the amount of energy available — is less than before.
As the jet stream slows, it meanders in bigger and bigger loops, like a big, slow-moving river crossing a flat plain. These huge loops – ‘Rossby waves', as they are called – tend to get ‘stuck' for a long time. Some pull Arctic air far to the south and hold it there, like last winter's Big Freeze in Texas. Others pull hot southern air farther north than usual, like last month – and they too hang around for a long time.
The two kinds of loops alternate along the northern jet stream around the planet like beads on a necklace. Every second loop is ‘hot' when this pattern kicks in, so it follows that the heatwaves would be happening in sync in several different continents – as they currently seem to be.
This is all quite new science, and still open to challenge. But over the past two decades, the same pattern of seven stalled peaks and lows over the same regions – ‘wave-7' – has lasted seven times for more than two weeks. Before 2000, it never happened.
We once believed that severe heating would not afflict the rich countries of the temperate zone until much later than the tropics and sub-tropics, but that may be wrong. We already have killer heat waves with the global average temperature up by only +1.1° C. It's bound to go to at least +1.5°C, even if we do everything right from now on.
