It's not all El Niño: Ottawa's warming winters part of longer trend

Warmer weather in Ottawa this winter has meant another year so far without the full Rideau Canal Skateway and the delayed opening of ski trails.

The lack of really cold weather also has the potential to spill over into summer.

"I could see it being a good thing for mosquitoes that we're having a winter like this," said Heath MacMillan, an associate professor in the department of biology at Carleton University.

Icy temperatures usually kill off more of the dormant mosquitoes waiting in egg form to come out in spring, MacMillan said.

But the frigid temperatures the city is known for have only showed themselves for a week in the middle of January. December and January came in milder than usual and February's even warmer on average.

While there have been zero days of –20 C in the city so far this winter, there were eight such days last winter, 25 in 2021-22 and five and nine respectively the two winters before that.

Ottawa hasn't even hit –10 C yet this month.

Insect populations affected

Cold is not the only factor. Whether you'll see more of the insects in a given year can be hard to predict, MacMillan said.

Warmer temperatures could also cause more to die as those cause them to use more energy: their metabolism runs faster when it's warmer.

"If they're overwintering as an egg, they only have so much energy stored in that egg. They might use it all up and die, but mosquitoes actually are more sensitive to temperature," he said.

Big swings in temperature can also kill off more of the population.

The biggest factor may still be to come, MacMillian said: the amount of standing water we'll have around in the spring from the snow melt, as that's where mosquitos spend the first part of their life cycle.

It's also been a dry winter: the last time Ottawa's international airport weather station recorded at least a centimetre of snow in a day was Jan. 24. There's only been about two millimetres of precipitation there this month.

As for ticks, MacMillian said the population will also depend a lot on the snow cover, which keeps their hibernation spots in the leaf litter insulated. A cold snap without that cover can be deadly.

In general, he said warmer temperatures help keep ticks alive.

Farmers praise warmer temperatures

One group with an eye on summer that is happy with the milder winter weather is farmers.

Farmers CBC spoke with say it has enabled them to get more jobs done on the farm than during a regular winter and it's been easier on equipment.

For example, when it comes to wild berry varieties sitting in a open field, the lack of cold wind is a bonus.

"When it gets super cold and windy, it just freezes it right down to the core and then it gets like a winter burn. It kills off your plant and then you have to dig it up and replace it," said Ann Marie Rochon, a farmer with Rochon Garden.

"This year we're really hopeful … We know that they'll be safe and they'll probably, you know, we'll start see them kind of coming back to life in the springtime."

As with the ticks, winter wheat farmers said a bit more snow could help keep plants insulated and protected in case a cold snap does come our way, which is possible with plenty of winter left. 

Climate researchers such as those involved in a 2023 Ontario report allow that there are some benefits to warmer weather for industries such as agriculture, fishing and recreation, but say the harms such as extreme summer heat outweigh the good.

Warming trend in region

This year's warmer temperatures are getting a boost from the El Niño phenomenon according to Geoff Coulson, a warning preparedness meteorologist with Environment Canada.

"Maybe that influence is going to be a bit stronger and certainly that's been borne out with the numbers we've seen temperature-wise for December and January," he said.

It's not just this year, said Coulson: data over the last 20-plus years shows a warmer trend. Five of Ottawa's seven mildest Decembers have occurred since 2001, with this past December coming fourth.

January temperatures show a similar trend.

"Cold air is is going to be around in the winter months in Ottawa, but it certainly looks like in the last 20, 25 years it hasn't made as much of an appearance as it did prior to prior to that," Coulson said.

As of 2010, Ottawa's average annual temperature was 6.7 C, 0.7 C warmer than the previous three-decade average. By 2100 it's projected to be 2 to 6 C warmer, depending whether and by how much humans cut emissions.