From a tropical storm drenching Southern California with record-breaking rain to unprecedented heat waves baking large swaths of North America to Canadian wildfires blanketing US cities with dangerous levels of smoke and air pollution, this year’s weather has been anything but normal. 
 
Given the realities of global climate change, these once-rare weather occurrences are the future of our forecast—with some caveats. 
 
In general, there will be increasing incidences of regionally extreme weather. The subtropical jet stream—a swift upper troposphere westerly wind in the northern hemisphere—is becoming increasingly “wavy,” with larger crests to the north and troughs to the south. This occurs because the polar regions are warming much more than the lower latitudes, decreasing the temperature differences between the tropics and the poles, which would normally constrain the jet’s meanders into tighter bands.

The larger crests associated with the wavy jet stream are allowing tropical air to shift northward into western North America. In June 2021, British Columbia saw a string of record-setting warm temperatures, topping 121 degrees Fahrenheit in Lytton, a village in the southern part of the province. Likewise, the troughs can drag cooler air from the Arctic down the east side of North America, which is why Texas had a large freezing event in February of that same year. The nine-day winter storm resulted in billions of dollars’ worth of damage, statewide blackouts, and hundreds of fatalities.

In addition to a dramatically wavy jet stream, the warmer temperatures are increasing the amount of water vapor—itself a greenhouse gas—in the atmosphere, resulting in higher rainfall totals and greater rainfall intensity on average in the United States. There are exceptions, such as Arizona and Hawaii, but overall precipitation and storm intensity will increase in the coming years.

At the same time, we must remember that not all regions will experience the same types of odd weather. Even if Texas has a very cold winter, you can be sure that some other region will be experiencing extra warm conditions, and the global temperature will continue to rise on average. Part of the reason for Hawaii’s horrible wildfires—which charred more than 2,100 acres and killed nearly 100 people—was winds associated with Hurricane Dora, which fanned the flames with 60-plus mph winds.

We are in the midst of an El Niño year. This happens every 4 to 11 years, warming the Pacific Ocean around the equator and driving up temperatures there and across the southwestern US. The prolonged heat waves this year in large parts of the west are driven by El Niño on top of the background warming from climate change. Some people think that climate change could increase the intensity of El Niño, but there isn’t consensus on that, and its intensity has changed in the past without anthropogenic climate change driving it.

While underlying natural cycles drive some of the weather oddities we see, there is no doubt that our emissions are creating more extremes. Increasing greenhouse gases adds energy to the atmosphere—and as that extra energy is redistributed around the planet, extreme weather results. Think of it as a pot of boiling water on the stove: as you crank up the heat, the water boils more vigorously. 

Extreme weather at a glance:

• 70 million Americans from New York City to St. Louis were under air quality alerts in July—the result of smoke from nearly 900 Canadian wildfires
• Tropical Storm Hilary dumped 2.2 inches of rain on Death Valley National Park—as much as it receives, on average, in an entire year 
• This past June was the hottest on record since global temperature recordkeeping began in 1850 
•  16% of Maui County was in a severe drought when the August wildfire—the nation’s deadliest in more than a century—ignited 
•  Phoenix recorded daily highs of over 110 degrees for the entire month of July, surpassing the previous record by 13 days 
• Both New York (2.3 inches) and Baltimore (0.2 inches) saw their least snowy seasons on record last winter