First Frost/Last Frost

Croci Waiting for Their Time in the Sun

On April 1st it snowed in Connecticut. Some got the joke, some didn’t. If I had a dollar for every complaint I’ve heard about our unpredictable, unreliable, unbearable spring weather…uh, I might be able to buy a tank of gas.

We had some serious snowfall in New England this winter, so I am not unsympathetic. But no one who lives here should be surprised.

That’s weather, not climate.  However…this might be a surprise:

Dying Soldiers 3/30/11 6:37am

In the United States, spring now arrives an average of ten days to two weeks earlier than it did twenty years ago. Many migratory bird species are arriving earlier…. Snow cover is melting earlier. Plants are blooming almost two weeks earlier in spring.
The Weather of the Future by Heidi Cullen

That’s climate, not weather.

Circa 1986

Last fall, I found an isotherm map printed in a 1986 “Backyard Gardener Calendar.” I became curious about the dates of the first frost/last frost. Have planting zones migrated? Is spring coming earlier?

Pick Stamford. Twenty-five years ago the map pegged the last frost for April 15, and the first frost for October 25–about 28 weeks between them. Frost is defined as temps below 28 degrees Fahrenheit, “destructive to most vegetation.” But the probability is not given: are those dates 10%, 50% or 90% likely?

I contacted the CT State Climate Center at UConn to ask about comparable figures for this year. Would they show a two-week difference since 1986?

A climate scientist named Zhao Xue, very helpful on the phone, emailed me a raft of information, including a NOAA link for isotherm maps with data from 1951 to 1980.

Place your bet here

The comparison with 25 years ago hinges entirely on probability.

Zhao sent me a NOAA link with freeze/frost dates for this year (U.S. Climate Normals). The “freeze free period” this year is highly likely (90% probability) to be longer than 25 weeks.  And it is highly unlikely (10% probability) to be as long as 30 weeks.

Do my 1986 “Backyard Gardener” dates fall within that range?  Yes they do–smack dab in the middle–50% probability.

Which is why the term “exact science” is a misnomer.  Science always deals in probabilities and ranges, and is always subject to later revision.

Indeed, Zhao emphasized: “I believe the dates are based on probability calculation (from previous experience)–not on real observation.”

Whose frost first?

For some real observation, I called Ted Mankovich:  computer scientist, horticulturist, photographer and mainstay of the Guilford Land Conservation Trust. Ted created a program that’s been recording the temperatures at his house every 10 minutes for the last 5 years. Who else does that?

Snow Tulips to Be 3/24/11 7:08am

But translating temperatures into frosts is not as simple as it sounds. We exchanged ideas, and Ted followed up with a blog post titled ‘Frost & Textures.’ Very entertaining—you can read it and see his great pictures here—but I will skip ahead to his conclusion:

We started with a question of whether I recorded the day of the first and last frost. We end with two new questions. What is your definition of first and last frost? How can you go from temperature readings to determining first and last frost? And we haven’t mentioned that frost is very territorial. My first frost isn’t your first frost even if we agree on what that is.

Groundhog Day in January!

On April 1st I also received this email:

The Union of Concerned Scientists and the town of Punxsutawney, Pennsylvania announced today that Groundhog Day will be pushed forward eight days to January 25 in 2012 in recognition of the impact climate change has had in the region.

The change is based on analysis by UCS scientists who found that, since 1997, spring has come an average of eight days earlier to western Pennsylvania.

But when I clicked through….
You just fell for an April Fool’s Day joke from the Union of Concerned Scientists! We hope you got a good chuckle out of it. But while these jokes may be funny, some people are trying to fool the public about climate change science every day of the year…

The UCS (of which I’ve been a member for some years) didn’t say whether they’ve actually documented a change in the arrival of spring in Western Pennsylvania.

I’ll give the last word to Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research: “It’s not the right question to ask if this storm or that storm is due to global warming, or is it natural variability. Nowadays, there’s always an element of both.”

Frosty Phragmites et al 12/17/10 9:12am

Note: All photos and captions (‘cept Punxsutawney) in this post are taken from Ted Mankovich’s excellent blog Olmsted Irregulars, and used with his permission. They were taken at Olmsted Outlook: a special one-half acre parcel located on the West River that was given to the Guilford Land Conservation Trust in 1981 by Howard and Deborah Weaver. The park and other GLCT lands are cared for by the Olmsted Irregulars with Ted’s enthusiastic and knowledgeable leadership.


About John Wackman

A writer since I learned to hold a pencil (no, not like that...hold it like this!). Long-time writer/producer for television, now organizer of Repairs Cafes in the Hudson Valley (13 & counting!) -- Program Manager of Solarize Hudson Valley, non-profit, state supported, community sponsored renewable energy program. We're all re-inventing ourselves. It's a sci-fi world, isn't it?
This entry was posted in Climate change + Culture, Deep Ecology, John Wackman blog and tagged , , , , , , , , , . Bookmark the permalink.

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  4. John,
    Don’t stop there. Here is further research for you. How do they translate the isotherm map into the USDA Plant Hardiness Zone Map? Next, if I give you my five or so years of temperature data can you calculate what the Hardiness zone is for my house? And how reliable would it be? How many years of data do they use in creating the Hardiness Zone Map?
    Looking forward to find my zone is 6.8b.

  5. wisewonderings says:

    Here in WV summer seems to be coming later and lasting longer, The transitional seasons are ever shorter from anecdotal observations over 10 years and talking to old timers in the valley. There will always be naysayers about climate change. My understanding is that w/ climate change there are more extremes of all sorts of weather associated w/ it.Weather is always local, right, but climate change is global. If we were polar bears or witnessed state sized bits of Anarctica crashing into the ocean, we would feel more impacted. But we live our climate controlled lives and really don’t see the great big picture, so we just talk about the weather. Thanks for such interesting reading, John.

  6. Cait says:

    Those must be hardy crocuses! I enjoyed your article and reading the explanation for your site’s name (I admire those poets/writers, too). So, would you say the jury is still out on whether spring is actually coming earlier?

    • John Wackman says:

      Cait: The warming is real, but from my reading of the science, we know two things: temp changes are greater towards the poles; and measurements will always vary due to local conditions. Thus, probability and range. I expect to hear from the Union of Concerned Scientists about the facts behind their April Fools’ email. I will keep you posted.

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