Our 14th warmest winter on record 'warns what will likely be coming,' climatologist says

Editor's note: This story was changed to correct the average temperature.

Chicago had an unusually mild winter this season - the 14th warmest on record going back to 1872. It's a phenomenon that state climatologist Trent Ford said is likely to become more frequent.

"The impacts of climate change are not just 30 or 50 years away; we're seeing them today," Ford said. "Seeing warmer winters like what we had this winter sort of warns what will likely be coming in the coming decades."

The average temperature this winter was 31.8 degrees, which is 3.7 degrees above normal.

While less of an immediate concern than warm summers, these types of mild winters raise cautionary flags in several areas, including agriculture and plant ecology.

Ford said perennial plants like fruit trees know when to come out of dormancy based on the temperature. That means these plants rack up a certain amount of "chilling hours," and when they've reached their naturally calculated quota, they wake up and produce flowers.

After a mild winter, farmers and gardeners alike face a balancing act. If their plants break dormancy too early because they've adapted to more frequent mild winters, they're at risk for damage when the spring freeze inevitably occurs.

This is particularly a concern for crops in the southern part of the state, like peaches, apples and cherries.

"We're in this kind of race right now between trees and shrubs breaking dormancy earlier than they normally would because of milder winters and an earlier last spring freeze," Ford said. "We won't see the last spring freeze until at least maybe the mid-part of April, even later in April depending on what happens in Chicago, which means that that puts our tender perennials at risk of having pretty significant damage. Ecologically, that's a problem we don't want."

Warmer winters can also throw a wrench in spring timing for pollinators. Ford said the vital critters respond to light more than temperature, meaning that as the climate changes but the period of light stays the same, there is a concern about misalignment between plants flowering and pollinators waking up.

"These matches have evolved over several millennia to work in our favor so that the squash bees come out when the squash is flowering," Ford said. "But those mismatches can mean that we have pretty significant issues when it comes to ecosystem health, pollinator health and in crop health."

While climate can be generally predicted by analyzing weather patterns over a long period of time, Ford said, weather - or the short-term state of the atmosphere - is much harder to pinpoint. That means that what type of spring we'll have is still up in the air.

"This year, I'm kind of on pins and needles to see what we get," Ford said.

In a region where it's usually reliably cold, understanding how mild winters will affect our environment in the long term is still a subject of research, said Christy Rollinson, a forest ecologist at the Morton Arboretum.

In the short term, Rollinson said warmer weather impedes winter restoration work. That's because when the ground doesn't freeze solid, the Arboretum's natural resources staff can't bring equipment into the woods without having to worry about compacting the soil.

"We weren't able to get a lot of that work done this year because we couldn't do it without creating more damage than good," she said. "That is a huge concern for us, and for a lot of the natural resources managers in the region. We're having to reevaluate how we get some of this work done, because we know this is going to happen again in the future."

Mild winters also spell concern for individual trees. If a tree puts out its leaves too early and loses them in a spring freeze, it has to try again. Rollinson said that is no easy task, and it can put a lot of stress on the plant.

"If we had this early leaf out and still get late freezes - because those aren't necessarily moving in sync - then we start to worry about the overall health of the tree," she said. "If that becomes a normal thing, it's unsustainable. That's something that I'm looking at and trying to use weird years like this to get information that can better help us know how that's going to impact the tree, both within a single year and then for the long term."

Rollinson added that the Chicago region is on track for earlier spring bloom times than is typical this year, but predicting when bloom season will occur can change on a week-to-week basis, especially for a region so uniquely located.

"We're seeing a lot of early leaf out and bloom across the U.S., but how the next couple of weeks go in terms of weather is really going to determine whether we follow that trend - or if we're going to be following the trend more of what we're seeing in Wisconsin, which is actually kind of cooler than normal," Rollinson said. "We're right in this transition zone."

Though we've had warmer winters in the past - for instance the winter of 1953-54 had an average of 32.3 degrees compared to this year's 31.8 - Ford said the weather conditions that make a mild winter are happening more frequently, and that is inherently at the hands of climate change.

"It's much more likely now than it was at the turn of the 20th century that we get a top five or top 10 warmest winter on record," he said. "It doesn't mean that we're necessarily going to break all the records, but we don't have to break records to see the effects of climate change."

Ford added that rather than evaluating how much of a weather event was due to climate change, a more salient question is to ask how much more likely it is that a weather event will reoccur.

"How much was this warmer winter a function of climate change? Well, whatever impacts that this warmer winter caused, the real question is how much more likely or how much more often are we going to see those impacts because of climate change in the future?" he said. "That kind of reframes the conversation to more of a preparedness, as opposed to a looking back on a past event."

• Jenny Whidden is a climate change and environment writer working with the Daily Herald through a partnership with Report For America supported by The Nature Conservancy. To help support her work with a tax-deductible donation, see dailyherald.com/rfa.