What Does “Unprecedented Climate” Mean?

Starting in just 30 years, the coldest year will still be hotter than any year in the past 150 years

Plants and animals living in the tropics will be pushed out of their natural temperature range the fastest.
Plants and animals living in the tropics will be pushed out of their natural temperature range the fastest. Steve Dunleavy

Surprising Science has a run-down of a new climate study that came out today in Nature. The study, as Joseph Stromberg writes, “used climate models to track how long it would take for weather events that are currently thought of as extreme to become typical.”

But what does that mean, exactly? Well, think back to the hottest year you can you remember. Now, picture this: Starting in around 30 years, that hottest year you remember will be colder than any year you’ll ever see again. The team of scientists, headed by the University of Hawaii’s Camilo Mora, that produced the study, call this an “unprecedented climate.”

The average temperature for any given year is not a set number—the Earth isn’t tuned to some giant thermometer. Instead, events like volcanic eruptions, the behavior of the Sun, or large-scale climate patterns like El Niño and La Niña mean that some years are warmer and some are colder. The range from the coldest year to the warmest year is the climate’s natural variability, and over the past 150 years or so the temperature has bounced around quite a bit.

Starting around 2047, assuming we keep pumping greenhouse gases into the air, the average annual temperature will be “continuously outside the bounds of historical variability”—the coldest year will be hotter than the hottest year from 1860 through the early 21st century.

That’s for the Earth’s temperature in general. When you break it down for different parts of the planet, some places will hit “unprecedented” territory even sooner. The tropics will get it first, within as little as 17 years.

Click to embiggen. A chart showing how the annual average temperature over a patch of the Atlantic Ocean has bounced around from year to year starting in 1860. Computer models projecting the future temperature show a similar up-and-down dance. Starting in around 2035, the lowest dip in the temperature is higher than the highest peak in the past temperature. And it stays this way. Photo: Adapted from Mora et al.

The swift pace of change matters, say the scientists in their study, because plants and animals (and people) are used to living within a certain range of temperatures. Some animals can take more variability than others, which you know if you’ve ever accidentally overheated your fish tank. But it’s the animals in the tropics (where the temperature is set to break into unprecedented territory the soonest), the scientists suggest, that animals are least able to cope with change.

It’s important to keep in mind that the research is looking at annual average temperatures, not daily temperatures. So, it doesn’t mean that every single day will be hotter than the hottest day you remember. Rather, the whole year will, on average, be hotter. A rising average also means that hot days will be hotter, and, while you’ll still get cold days, they will also probably be hotter, too.

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