Maple Syrup and Climate Change: Another Angle to the Sappy Story

by Allyson Green on March 18, 2013

March in the Midwest brings maple syrup season—a time when maple trees across northeastern North America are tapped for their sugary sap. Having spent two season happily tapping trees in Wisconsin, I still instinctively take note of temperatures and tree types as I walk through town this time of year. Not having maple trees of my own right now, I am left to rely on my local syrup makers for my yearly supply of this essential food group. So, imagine my dismay at the increasingly dismal outlook for Sugar Maples in North America. In the face of climate change, these trees are experiencing declines due to range limits, soil acidification, pests, and even lack of decomposition on forest floors. The body of research and reporting on climate change impacts is growing, but my hours spent sitting next to an oil-burning evaporator during my syrup-making days brought to mind another angle to consider in the story of syrup:

To what extent does the maple syrup industry actually contribute to the climate change threatening its future?

Step 1: Find a maple tree, tap it, and wait for the sap to flow.

Google was surprisingly unhelpful in answering that question. So if at first Google does not succeed, try again… with an easier question. First, we need to look at syrup production. Because production is completely weather dependent, with trees needed temperatures below freezing at night and above freezing during the day, the total amount of syrup produced varies annually. In 2009, trees and their tappers around the world (which really just means Canada and the U.S.) produced 13,320,000 gallons of maple syrup to sell commercially. That syrup starts as sap which is collected, boiled, bottled, and shipped to people across the world.

It typically takes about 43 gallons of sap to make 1 gallon of syrup. To boil off the 42 gallons of water in that sap, it can take up to 4.1 gallons of fuel oil, though efficiency measures can reduce that to 3 gallons.  If wood is the fuel of choice, a cord of wood can get you 15 gallons of syrup.

Step 2: Collect the sap from your buckets. Try not to spill it in the snow.

A 2003 survey of Wisconsin syrup makers showed 46% of syrup was made using wood and 48% using fuel oil. If we were doing a more accurate accounting of fuel usage in maple syrup production, we wouldn’t base all of our calculations off this one study (might people in Quebec use more wood than oil?), but since it was the only one I could find, we’ll use these numbers and keep in mind that this assumption could lead to inaccuracies in our final estimate.

  • 48% of 13,320,000 = 6,393,600 gallons of syrup made with fuel oil in 2009
  • 46% of 13,320,000 = 6,127,200 gallons of syrup made with wood in 2009

 Note: Using production numbers from 2009 and fuel use numbers from 2003 isn’t completely fair either. We’ll also just ignore the leftover 6% of syrup produced using neither fuel oil nor wood for now.

  • 6,393,600 gallons of syrup x 3 gallons of fuel oil/gallon of syrup = 19,180,800 gallons of fuel oil used in 2009
  •  6,127,200 gallons of syrup ÷ 15 gallons/cord = 408,480 cords of wood used in 2009

Another note: We’ll assume most producers are using efficient evaporating techniques that use only 3 gallons of fuel per gallon of syrup.

Step 3: Evaporate all the water. Enjoy the steam.

While carbon dioxide (CO2) is not the only greenhouse gas of concern when it comes to climate change, we’ll use this as an indicator of climate change impact because the data is readily available. Using the EPA’s estimate of CO2 emissions from fuel oil, we get:

  • 19,180,800 gallons of fuel oil x 1/42 gallons/barrel x 429.61 kg CO2/barrel = 196,196,749.71 kg of CO2 emitted from boiling sap with fuel oil in 2009

And since this Swedish study estimates that wood burning produces about 60% of the total CO2 emissions of oil, let’s try this calculation:

  • 196,196,749.71 kgCO2  ÷ 15 (because it takes 15x less wood than oil to make 1 gallon of syrup) x 60% = 7,847,869.99 kgCO2 from boiling sap with wood in 2009

Yet another note: I completely disregarded the 2% difference in production of syrup using wood vs. fuel here. My math skills are failing me. Also, the 60% emissions estimates takes logging and transportation into account, but a lot of maple syrup producers use their own wood for fuel. I have no idea if the estimate of fuel oil emissions accounts for production or just burning.

In 2009, all of us humans collectively produced 31.3 billion metric tons of CO2. So, our last calculation of the day gives us:

  • (196,196,749.71 kgCO2 + 7,847,869.99 kgCO2) ÷ 31.3 billion metric tons  =  0.000000656 x 100% = 0.0000656% of total CO2 emissions in 2009

Well, that’s kind of anti-climactic after all that math.

But do you buy my math? How many of my assumptions were valid? And what else is missing from this calculation?

Step 4: Bottle and distribute your syrup.

To chase down a better answer to my original question, we could calculate the increase in acid rain from these CO2 emissions or maybe predict how much it contributes to temperature rising (Edit: As Robb points out below, the impact on acid rain would need to be calculated from the accompanying sulfur dioxide and nitrogen oxide emissions and not just CO2). But I’ll save that for the climate scientists among us.

This emissions-calculating thing is tough. My estimates here would not stand up to the peer-review process, since I’m missing a lot of information and making a lot of assumptions. My appreciation for folks that actually estimate emissions has just grown exponentially!

I guess if you can put any trust at all in these very rough estimates, you might feel a bit of sympathy for maple syrup producers. Their livelihoods seem to be affected disproportionately by climate change. Yes, their production and transport of maple syrup contributes to climate change more so than the maple syrup producers of old, but they are making strides to become more efficient in energy use.

So, enjoy your next pancake brunch with real maple syrup…while it lasts!

Step 5: EAT!!!

Robb March 18, 2013 at 3:00 pm

I appreciate how you walk through the calculations pointing out the areas of certainty for the reader. IMHO, communicating uncertainty to the general public is tough, but important in science writing. At the same time, I think that the step by step calculation is interesting to others who like numbers and using them to estimate impacts, but it could get a little tedious for a wider audience. At any rate, I enjoyed the post. One correction: sulfur dioxide and nitrogen oxide contribute to acid rain, not carbon dioxide.

Allyson Green March 18, 2013 at 7:25 pm

I admit, after writing out those equations…even I don’t want to go back and actually read them :). And thanks for catching the point about carbon dioxide and acid rain. I think I made a few leaps in analysis in that sentence that didn’t make it from my brain to the page.

Thanks for the feedback!

David Reedy March 18, 2013 at 4:50 pm

I agree with Rob, I thought the walk through with indications of uncertainty were appropriate. I think it gives a taste of what science reporters have to go through.

As a further item to check – when trees die and rot in the woods, do they give off CO2? If so, how does burning wood’s CO2 emission compare to the rotting wood’s CO2 emission?

We tapped our own maple trees from 1946-1993 and boiled it down in our 1814 fireplace complete with crane. It was a monster that would take a 48″ log in the back. I’m pleased to find out we were only miniscuely reponsible for global warming.

Allyson Green March 18, 2013 at 7:52 pm

Sitting in front of a giant fireplace watching sap boil sounds much more pleasant than my experience with an old, leaky, fuel-oil powered evaporator! Someday I’d like to try the fireplace method :)

Trees rotting in the woods do give of CO2, which is why burning biomass is often considered “carbon neutral.” The Swedish study I referenced here argues that shouldn’t be the case though, since the CO2 from decomposition is released over years while the CO2 from burning is instant. Some of that carbon from decomposition ends up in the soil as well. I’m not finding any good numbers on CO2 emissions for those processes right now… but I’ll keep my eyes out!

Michael March 19, 2013 at 12:05 am

Have they tried controlled burns to open up the forest floor?

Allyson Green March 19, 2013 at 9:41 pm

Good question! As far as I can tell, the researchers who first reported on sugar maples not being able to grow through thickening underbrush have not done any controlled burn experiments. Sugar maples tend to be sensitive to fire, so it would be interesting to see the trade-off between clearing the forest floor and potentially reducing existing sugar maple density after the fire.

Lola March 22, 2013 at 7:25 am

I have noticed the rising price of maple syrup over the years. Would you be in favor of a “syrup tax”?

Allyson Green March 22, 2013 at 10:29 am

Hmmm….a syrup tax. I hadn’t considered that! The only “syrup tax” I know of right now is for soft drink manufacturers. I think I could be supportive of a maple syrup tax if the extra revenue went into something like climate change research or went into programs that directly benefit the syrup makers. With the prices already on the rise, though, I would hate to see people switch over to the fake stuff because they couldn’t afford the extra tax on the good stuff anymore!

Angela March 25, 2013 at 7:34 pm

Hi Allyson! I also liked how you pointed to the difficulties of quantifying environmental impact, e.g. how much of the figures are estimates or generalisations from smaller samples. At the same time, you do not dismiss the value of these provisional figures, and suggest that they enable a certain handle on a topic that would otherwise be impossible to portray to e.g. syrup producers, policy makers. If you wanted to add another level of messiness to the issue of representing such a problem, you could put the maths into different sorts of diagrams! 😉 I loved the photos by the way!

Allyson Green March 25, 2013 at 10:18 pm

A visual sounds much more fun than equations! Maybe that’s a project for another blog… :)

Angela March 26, 2013 at 7:02 am

If you want to try it out in another blog post, here are two books I like to use as examples. First, there is a very old-school book called ‘How to Lie with Statistics’ from the 50s that’s pretty interesting to read, also as a historical document (there is a free download here: ). It has some graphics bits in it, too. In terms of more recent stuff, Edward Tufte’s work, e.g. The Visual Display of Quantitative Information, is very thought-provoking.

Allyson Green March 28, 2013 at 8:31 pm

The title is intriguing enough to warrant a read! Thanks for the tips!

Ray Fortune May 9, 2013 at 7:29 am

We are a maple syrup pruducer using a high efficiency oil fired evaporator and an Reverse Osmosais unit. The ratio of oil to syrup with this set up is 1 to 1 not 3 to 1. We could reduce this further if we increase the level of sweetness from the RO. I assume similar effeciencies will apply to wood fired evaporators.

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