Chicago’s 2023 winter season has been mild, with snowfall at the lowest it has been in 12 years. To clear the roads of the 18 inches of snow that did fall, the city’s Department of Streets and Sanitation used 132,363 tons of salt, or less than a third of its annual inventory, to prevent slippery driving conditions.

There wasn’t a lack of precipitation this winter in Chicago — it was just warmer. Snow that Chicagoans would normally expect in December, January and February turned to freezing rain and sleet, a hazard that Streets and Sanitation spokesperson Mimi Simon said is even more concerning than snow when it comes to black ice.

“The amount of snow is only one factor to be considered” for the amount of salt needed, Simon said. “We also take into account the amount of salt we will need for wintry-mix weather like freezing rain, ice and sleet.”

But the warmer weather also meant less of a need for salt.

As human-induced climate change boosts the effects of natural weather patterns, Chicago could be on track for warmer winters and less snowfall. This winter it was more than 10 inches below average.

[ How our 2022-23 seasonal snowfall compares with previous winters ]

The period from Dec. 1 to the end of February was the city’s fourth warmest in the last 70 years and the 14th warmest since records began in 1872, according to Illinois state climatologist Trent Ford.

So what happens to the salt that isn’t used?

“Salt does not expire,” according to Simon.

The start and end of the snow season “is up to Mother Nature,” she said.

Typically, the department buys salt in bulk, at $66 a ton, after the season ends to replenish its supply.

Streets and Sanitation used to start out the season with 375,000 tons of salt but upped it to 425,000 after 2017. Simon said there were past seasons when the city would have to buy more salt during the middle of winter, which was difficult to transport at that time of year.

[ Chicago region grapples with reducing road salt as chloride levels exceed state limits in waterways, continue to rise in Lake Michigan ]

This year, the city spent a bit over $18 million to refill the supply of salt from the year before.

It might not be a surprise that the city gets its fix of sodium chloride from Morton Salt.

That means the salt that stays on your fingertips after eating a bag of chips is the same salt you see on the street. Streets and Sanitation buys a chunkier grade of salt and mixes it with beet juice to prevent ice from forming.

There are 19 locations where salt is stored in the city, and the department has more than 300 snowplows. Resembling a large snowball from the outside, the latest location was built in 2021 near Grand Avenue and Rockwell Street.

rrequena@chicagotribune.com