Ask Eric: Are Winters Getting Warmer?

I remember it being  a lot colder in winters past. Have the winters have gotten way too warm? What is your opinion on this?

-Thank you, Nick

It's a common refrain - I remember it being so much colder/stormier when I was younger! I think we all feel that way. I know all the storms seemed like blockbusters and the winters often harsh when I was younger. While anecdotal weather can be helpful - there's really only one true way to look at weather in the past. And that's the observed data. No doubt, it's not perfect either. Ways we measure snow have changed, locations of climate sites have changed, and human influence on weather reports have changed (new technology, land use changes, etc). So it can often be difficult to separate signal from noise. But for Nick here, I'm going to take a little peak into our past recorded winters and see if his thoughts are true.

For starters, here's a look at the average winter temperature since records moved to Logan in 1936 (meteorological winter being December/January/February). I use the 1936 measuring stick because the old site used to be inside the city of Boston, which was undoubtedly a colder place than the current airport location on the water. This is especially true in winter, when our coldest temperature readings often come from radiational cooling nights. These are much harder to come by on the water than they are away from the immediate coastline. You'll easily spot this if you look back through the temperature record. A large majority of Boston record lows are still standing from the 1800s.

What you see is that there's plenty of variability from year to year.  But a couple of things stick out to me. The first is that we tend to bottom out with a truly bitter winter ever 8-12 years. You see low points of average temperature in the late 40s, late 50s, late 60s, late 70s, mid 90s, early 00s, and last winter. That's a pretty even spread when it comes to a bitterly cold winter. The return interval of one of these types of winters is pretty consistent. So it's not as though we have seen a drop-off in those extreme seasons.

Seen another way, here's a table of the Top 20 coldest winters on record in Boston since 1936. Again, we see a pretty even spread. Older decades lead the way, but last winter was not far behind (a warm December kept us away from a more impressive finishing point). What many, like Nick, do remember, are the harsh winters of the 60s and 70s. And this table shows that nicely. 9 of the Top 20 all came during those two decades. It was a harsh time for the Northeast, and you may recall that 'Next Ice Age Coming' headline from Time magazine that has now become quite infamous. So when you say 'it seemed colder' - if you vividly recall this era then you're right!

Overall we have seen some larger extremes in recent years though. Some of the warmest, coldest, snowiest, and least snowy winters have all occurred very recently. In 2012? Just 9.3" of snow in Boston. Last year? 110.6" of snow. The top 2 warmest winters on record in the past 14 years. Last winter? The coldest month ever recorded in the area and records set for coldest stretches. Amounts of ice seen only once a generation. We've been all over the place.

What's the reason for this? It could just be a volatile era for us. These periods come and go, just as busy stretches for hurricanes come and go. A lot of that has to do with larger climate drivers like the PDO (Pacific Decadal Oscillation), ENSO (El Nino Southern Oscillation), and the AMO (Atlantic Multidecadal Oscillation). Certain phases/combinations of these ocean oscillations have been known to cause significant changes to weather all over the world.

Average temperatures have slowly but surely been rising since the late 1800s. This data from NCDC (National Climatic Data Center) shows the trend of average winter temperature in Massachusetts. Source: NCDC

Is some of it climate change? You can't rule that out either. I'm not interested in the politics of climate change, but of course the climate is changing as it always has and always will. We've seen gradual warming over many decades, and our oceans are running very warm right now. We must be wary of connecting the last couple of years, or even a couple of decades, and calling it a major trend. We all remember the last few years because they've been wild. But you can't extrapolate that line out linearly into the future. Just because we've had a few crazy winters doesn't mean every one ahead will be the same. We may dive right back into a ho-hum 10 year stretch of typical winters. There isn't a very good way of knowing whether or not that will come to pass.

What we do know is that yes, on average, winters are getting warmer over time. But the harshest winters are still coming around and not slowing down.