We’ve just had the second consecutive winter with no sub-freezing temperatures in my part of Florida, a weather occurrence I rate as freakishly unusual.
I’ve been living in Florida since the mid 1990s, and in my area (between Ocala and Gainesville), winter usually features a number of cold fronts that drop overnight temps down to the low to mid twenties F, and a cold winter will dip into the teens. The only other time I’ve seen a year without significant freezes here was the winter of 1997-1998, when a super El Niño produced weeks of rainy, overcast weather during the portion of the year when powerful cold fronts normally push into the state. But during these most recent two winters, there were no long cloudy periods, no super El Niño.
During both recent winters, a number of cold fronts dropped the temperature low enough to create patches of frost in open areas, so the temperature on surfaces where the frost occurred was definitely at 32F (0C). I think my local weather station recorded official temperatures of 32F a few times both winters.
I took precautions during those cold spells, putting covers over tender plants every time the weather forecast predicted lows anywhere close to the freezing point.
But it turned out my efforts to protect vegetation were unnecessary. Frost sensitive plants came through with virtually no damage, even out in open areas exposed to the sky. Plants are great thermometers – they show the air temperature never dipped below freezing for any significant length of time.
This recent pair of extraordinarily warm winters comes after a string of years with warmish winters. It’s been almost a decade since my area has gotten a really cold winter, with temperatures dipping to 20F or below.
So this brings up the elephant-in-the-room question: are these recent warm winters the result of climate change? That’s what I am trying to understand, and I’m finding the answer is not clear.
Average temps are definitely rising due to climate change. But since extreme winter lows can happen as a result of a the jet stream getting particularly wavy in winter, rising average temps don’t necessarily translate into rising lowest-temps-of-the-winter. It’s possible get brief vegetation-killing extreme cold snaps even as average temps creep upward due to climate change. Some of Florida’s worst historical freezes came during winters that were quite warm on average. And at least some climate scientists think that climate change is making the jet stream get wavier in northern hemisphere winter, potentially increasing the chances of extreme cold snaps.
Based on my own personal experience, I’m leery of calling a trend based on the weather patterns of a few years. When I first arrived in Florida in the mid 1990s, the previous decade-and-a-half had featured some extremely cold winters. I heard any number of gardeners say, “Winters in Florida are definitely getting colder – things that used to grow here can only grow south of here now.” Then the 2000s had a string of milder winters, and I heard people say, “Winters are definitely getting warmer due to climate change, so we can plant out more tropical stuff now.” Then we got the brutal winters of 2009-2010 and 2010-2011, when temps dropped repeatedly to 15F (-9C) at my location in north Marion County, and all talk of “winters getting warmer” stopped for a few years. Now that we’ve had another round of warm winters, that kind of talk is back.
I’m trying to figure out if this recent string of warm winters is a statistical fluke or a trend. If it really is a trend, then we can cautiously start planting out tropical fruits in areas where previously they would have been unthinkable. (Many people are not waiting – I’ve seen a number of fruiting mango trees in yards in the Orlando area the last couple of years.)
I’m looking for some data on this. I’ve been trying to find a data set that shows, for any location in Florida, what the lowest-temperature-the-the-year was for each year of that location’s entire temperature record. I thought this info would be easy to find, but it’s turned out to be surprisingly elusive. I’ve checked any number of online resources, and asked several knowledgeable people, and so far no one’s been able to point me to some place with this info. Even the USDA’s website featuring the official zone map (which is based on exactly this info) doesn’t seem to offer the raw data the map is based on. I’ve found a number of places which have records of the monthly average minimum temperature. But the most important weather factor determining which plants can and can’t grow in an area is not the monthly average lows, it’s the extreme lowest temperature of each winter. That’s what I’m looking for – the plant killers.
At this point I’d be happy to find even a data set of what the daily high and low temps were for each day of each location’s temperature record, so I can parse the data myself to get numbers for each year’s extreme low. I know this information is out there, it’s just a matter of tracking it down, and once I find it I’ll make a post about it. If you can help direct me to that kind of data, please leave a comment on this post or direct message me.
Just in case milder winters really are a trend, I am planting out a few tropical fruits in the ground. I’m trying to focus on own-root trees rather than grafted, so that if the tree ever does get frozen down, it can grow back as the same good fruiting variety, rather than a rootstock. More on that in another future post.