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About this blog: Climate change, despite its outsized impact on the planet, is still an abstract concept to many of us. That needs to change. My hope is that readers of this blog will develop a better understanding of how our climate is evolving a...  (More)

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What is a "ton" of carbon dioxide anyway?

Uploaded: Dec 1, 2019
When I first started reading about climate change and all of the carbon dioxide emissions, I wondered what they meant by a “ton” of carbon dioxide, or “tonne” as it was sometimes spelled. I know what a normal “ton” is. The weight of a VW bug has always been my reference point, though I guess the modern version is a Mitsubishi Mirage. It’s 2000 pounds. But the numbers I was reading about were so huge it didn’t make sense. For example, driving a car about 2500 miles releases one “ton” of carbon dioxide into the air. Here’s my mental image of that, complete with the aforementioned Mitsubishi Mirage:

One ton of something (in this case, a car) in the sky

There’s no way driving just 2500 miles does that, right? We would be releasing about a pound of CO2 for every mile driven. A pound of a gas, in just one mile? Gas doesn’t weigh that much! So what do they mean by a “ton of carbon dioxide”? I figured since it was also sometimes spelled “tonne”, maybe it was an obscure European metric unit of volume.

Amazingly, no, they actually mean a ton, as in 2000 pounds. Of a gas!!! So, yeah, our cars release about a pound of carbon dioxide for every mile driven! And that’s if you are getting 25 miles per gallon.

This car puts about two pounds of CO2 in the sky for every mile driven.

It makes you wonder, how heavy is carbon dioxide? Here’s a quiz. If you were to empty a gallon container of milk and fill it up with carbon dioxide gas, how much would the CO2 weigh? (Not the container, just the CO2.) Assume everything is at standard pressure and room temperature (70 F). Your choices are in increasing order of weight. (1)

The answer, to my surprise, is the 9x9 piece of cardboard, or about 7 grams. I never would have guessed that a gallon of carbon dioxide gas weighs that much! In comparison, the nickel weighs about 5 grams, the penny about 2.5, the AAA battery about 12. (2)

So the weight of carbon dioxide gas is, at least for me, very surprising. It is not all that light! And FWIW, while carbon dioxide is heavier than air, it’s not that much heavier. Air weighs about two-thirds as much. So -- the weight of these gases is not intuitive, at least for me.

Now let’s look at volume. If you want to translate to cubic feet, you can get about 7.5 gallons in one cubic foot. That means a cubic foot of CO2 gas weighs a little over 50 grams, or about 1.8 ounces. With 16 ounces in a pound, you get one pound of gas in just 8.7 cubic feet. So when you drive a mile, the carbon dioxide emitted fills up a 2’ x 2’ x 2’ space, or less than the inside of your refrigerator, and weighs about a pound. If you found a biggish Eichler -- a 2200 square-foot single-story house with 8 foot ceilings -- and filled it up with carbon dioxide, you’d get your ton.

To be fair, CO2 is mostly oxygen by weight, with 32/44 or about 73% oxygen. The oxygen is pulled out of the air when we burn the liquid hydrocarbons (fuel). So the net weight we are adding to the air is only about one-fourth the weight of the emissions. But still…

Carbon dioxide molecule with atomic weights

Another way to think about how much carbon dioxide weighs is to consider the solid form, also called dry ice. You can get a bag of it from Diddam’s for about $15.

A bag of dry ice (solid carbon dioxide)

The block of dry ice in the bag is about 9 inches by 7 inches by 2 inches and weighs about 7 pounds. You can use a conversion chart (3) to check that this amount of dry ice yields about 62 cubic feet of carbon dioxide gas. That means it expands by about 850x when it converts from a solid to a gas. That seems “about right” to me.

This shows the size of a seven-pound block of dry ice, aka solid carbon dioxide

But I still have trouble wrapping my head around the weight of carbon dioxide, or air for that matter. Think of all the air up above our heads. Our atmosphere is about 300 miles high, but most of it is in the first ten miles (aka the “troposphere”). So each of us has about 10 miles of air pressing down on us, which adds up to 14.7 pounds per square inch of surface area. Do you ever have trouble getting up in the morning? Maybe it’s because your body is waking up to the fact that there is a big weight pressing down on you….

How can we tell that air is actually that heavy if we don’t seem to feel it? One indication is air pressure. You probably know that when you go up to higher altitudes, the air pressure drops. The reason that air pressure is higher at lower elevations is because all the air above is squishing down on it. Seriously. The lower the altitude, the more air is pressing down, so the greater the air pressure is. Given that, you’d think when you got up higher on a mountain, you’d be walking with a real spring in your step. In Tahoe for example, at lake level (6000 feet), you’ve got only 11.8 pounds per square inch on you instead of 14.7. (4) On top of Shasta? A mere 8.6 pounds per square inch. On top of Everest? A negligible 4.4 pounds per square inch. But I don’t exactly see people bouncing around up there, even with oxygen.

Everest photo courtesy of Wikipedia

Science can be weird. It helps when it’s intuitive. Otherwise you just have to think about it until it makes sense. I’m still working on this part of it ...

Notes and References
1. In case you are wondering, the (approximate) weights I have are:

You can find some fun measurement data here.

2. The gallon of carbon dioxide actually weighs about the same as a human eye, but I thought that might gross some of you out, so I used cardboard instead, though I could also have used seven dollar bills (each bill is 1 gram).

3. This is a useful conversion chart from Liberty Gases:

4. There’s a helpful table of air pressure vs elevation here.

5. In case you are wondering, a “tonne” is a “metric ton”, also abbreviated “T”, and is 1000 kg or about 2205 pounds.

Current Climate Data (October 2019)

To stay below 1.5 C of warming, emissions in 2030 need to be 55% lower than in 2018. That is a 7% decrease every year. Yet 2018 emissions for the US, the world’s second biggest emitter, were up 2.7% last year, the largest increase in eight years.

Global impacts, US impacts, CO2 metric, Climate dashboard (updated annually)

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Posted by Resident, a resident of Another Palo Alto neighborhood,
on Dec 1, 2019 at 9:12 am

A ton is a unit of measurement in US as 2000 lbs. (This probably came about the same time as an American pint was changed to 16 fluid ozs instead of 10 fluid ozs)This is often called the short ton.

A ton is a unit of measurement elsewhere as 2240 lbs. This is often called the long ton.

A tonne is a unit of measurement for 1000 kg. It is often called the metric tonne.

Mass or weight is generally measured by tons or tonnes.

Posted by Tom, a resident of Menlo Park,
on Dec 1, 2019 at 3:59 pm

One way to think of a ton of CO2 is to look at how much atmosphere it has pushed from the "safe" level of 350 parts per million (PPM) CO2 concentration to the current unsafe and growing 410 PPM level. You can see levels here:
Web Link
60 PPM is the present excursion beyond the safe zone. (410 - 350) and the average of gasses in the atmosphere has a molecular weight of about 28 grams/mole compared to the 44 grams /mole weight of CO2. So in the 14.7 lb. of atmosphere stacked above a square inch of earth surface there are 60 PPM of unsafe CO2 weighing in at 0.0014 lb. / square inch ( 60 / 1,000,000 X 44 / 28 X 14.7 lb. ).
One ton of CO2 is enough to endanger the atmosphere above 1,429,000 square inches ( 2,000 lb. / 0.0014 lb./square inch). That is, one ton of CO2 is the level of excess CO2 we now have above 9,920 square feet of earth surface (1,429,000 / 144 sqin /sqft). Coincidentally that is the approximate size of an average small $2million Palo Alto residential property. Also about a 1/4 acre. Luckily I can buy a carbon offset ton for less than $20. Web Link
Such a deal.
But if my carbon footprint is about 10 tons per year ( I'm a careful consumer who limits beef and flying and natural gas), I'm still ruining the atmosphere over 10 properties per year. That seems like I'm living large and I need to work on further reducing my impact on other people, especially future people.

Posted by musical, a resident of Palo Verde,
on Dec 2, 2019 at 8:36 am

We generate 3 billion tons CO2 every year by simply breathing.

Posted by Sherry Listgarten, a Almanac Online blogger,
on Dec 2, 2019 at 11:37 am

Sherry Listgarten is a registered user.

@musical -- I love that comment, and not just because it gives me a good excuse to not exercise :) (While the average person exhales 2-3 pounds per day, it’s a lot more when exercising.)

Our breathing is obviously a very small proportion of our daily emissions*, and one of the harder things to cut back on (!) But a more general point is that these emissions are part of a relatively short-term natural cycle, unlike fossil fuel extraction and combustion. In a similar way, water vapor is part of a very short-term cycle, so even though it is extremely effective at retaining heat, scientists don’t seem to focus on it as much. I have got to hope that it is both politically and technically easier to cut way back on fossil fuel use than to dry out our ecosystem or worry about our own breathing...

* Our average per-person daily emissions are well north of 100 pounds in this area, not including the large amount of indirect emissions from our consumption of products and services from elsewhere.

Posted by Mitchell Zimmerman, a resident of Green Acres,
on Dec 3, 2019 at 12:42 pm

What a great idea, Sherry, to offer a series of articles making climate change more concrete for us.
One suggestion is that when you get to discussing what we have in store for us if we can't reduce atmospheric carbon dramatically, is to use 2030 or 2040 as the touch points. Many articles that summarize scientific projections talk about sea level rise and other events as of 2100. But since essentially none of us over the age of 15 will be alive then, I think that for most people this counts as the distant future. Better to describe the disasters that we and our children will experience over the next two decades. Thank you.

Posted by Sherry Listgarten, a Almanac Online blogger,
on Dec 4, 2019 at 9:41 am

Sherry Listgarten is a registered user.

@Mitchell, thanks for the suggestion. I think it's a good one, though the answers may not be as crisp as you'd like. One of the tricky things about reporting on the impacts of climate change is that they are so often couched in terms of probabilities. "Climate change makes xyz 30% more likely". Our knowledge is also limited. We don't know enough to accurately predict many significant changes, such as the melting rate of the Greenland ice sheet, the way in which the ocean circulation will evolve, or the speed at which various species will go extinct and/or adapt. The uncertainties are even greater over the short-term, though we are already experiencing impacts. Anyway, I'll see what I can do. Thanks again for the suggestion.

Posted by David Coale, a resident of Barron Park,
on Dec 4, 2019 at 10:04 pm

Thanks for your efforts to describe a ton of CO2, a gas we can't see and that is causing a lot of trouble. The one pound per mile is a pretty good estimate to use for this. Many years ago I was trying to help people visualize how much CO2 is produced from our driving and here is what I came up with: Let's say the average car is driven 10,000 miles per year. This means the CO2 emitted from this driving is 10,000 Lbs or 5 tons per year. The amount of CO2 produced every day is 10,000/365 = 27.4 Lbs per day! This is about the same weight of 3 and a half gallons of water. Imagine trying to carry just three one gallon contains of water. This is a pretty good amount. In the end, my visualization was to think about how much CO2 a car produces each week. This would be about 192 lbs per week. So each week this much CO2 is dumped into the atmosphere , for free, each week for the average car or as you point out twice this much for an SUV. Now imagine if we could actually, somehow, collect this CO2 and have it taken “away" on trash day. This would be three extra cans of “trash" weighing about 64 lbs each, quite a hefty haul to the curb, if we could have it taken “away". For many families that have two cars, one of which is an SUV, that would be 9 extra cans on trash day for each house in a residential neighborhood. Wow! Imagine what the street would look like. It would be lined with garbage cans and you would hardly be able to get out of your driveway!

Posted by Sherry Listgarten, a Almanac Online blogger,
on Dec 5, 2019 at 10:07 am

Sherry Listgarten is a registered user.

@David -- that's a great analogy. I expect it would make a big difference if all these problematic emissions were more visible.

Posted by Alan, a resident of Menlo Park: Belle Haven,
on Dec 5, 2019 at 10:17 am

The thing that always surprises me (but it shouldn't) is that the emissions have more mass that the fuel burned - because of the oxygen from the air gets combined with the carbon. Because carbon dioxide is less dense than gasoline, a sloppy, faulty intuition might lead some to think that the carbon dioxide has less mass; but the opposite is true: burning a ton of gasoline results in 3-4 tons of carbon dioxide.

Posted by Resident, a resident of Another Palo Alto neighborhood,
on Dec 5, 2019 at 11:29 am

If anyone here is interested in my post with the definitions above, I'm afraid I made a typo. The first paragraph is incorrect. Of course it should read the same time as a pint became 16 fluid ounces instead of 20 fluid ounces.

Here is the corrected paragraph.

A ton is a unit of measurement in US as 2000 lbs. (This probably came about the same time as an American pint was changed to 16 fluid ozs instead of 20 fluid ozs)This is often called the short ton.

Posted by Anon, a resident of Another Palo Alto neighborhood,
on Dec 5, 2019 at 12:55 pm

The following table, found here: " www eia gov/" tools/faqs/faq.php?id=73&t=11 shows the pounds of CO2 emitted per million British thermal units (Btu) of energy for various fuels

Coal (anthracite) 228.6
Coal (bituminous) 205.7
Coal (lignite) 215.4
Coal (subbituminous) 214.3
Diesel fuel and heating oil 161.3
Gasoline (without ethanol) 157.2
Propane 139.0
Natural gas 117.0

For most uses, the thermal energy is the goal, so, this is why natural gas is so preferred over coal.

On a related subject, there is more talk lately of carbon taxes and what they should be. A consortium of energy companies has proposed $40/ton of CO2. "www theguardian com/" environment/2017/jun/20/exxon-bp-shell-oil-climate-change . Exxon itself years ago calculated around $70/ton as being the minimum necessary to get the economic ship to change course: Web Link (warning, this article does not carefully distinguish US tons from metric tons). So far as I know, only Switzerland and Sweden have carbon taxes that high, although I don't have a current complete list. Here is one page: Web Link

Note that it is difficult to keep tons (US) v. tonnes (metric) clear in many news articles. I apologize in advance if I made such a mistake myself. If in doubt, check the sources.

Posted by Sherry Listgarten, a Almanac Online blogger,
on Dec 5, 2019 at 4:06 pm

Sherry Listgarten is a registered user.

@Anon, FWIW, coal has many problems besides carbon dioxide emissions, including dangerous particulates and waste (e.g., coal ash). Also, the numbers you cite for gas do not include the methane leaks, which are significant. We need to keep all this stuff in the ground.

Posted by Anon, a resident of Another Palo Alto neighborhood,
on Dec 5, 2019 at 5:57 pm

Posted by Sherry Listgarten, a Palo Alto Online blogger,

>> @Anon, FWIW, coal has many problems besides carbon dioxide emissions, including dangerous particulates and waste (e.g., coal ash).

Not to mention mercury and radioactive emissions. Unfortunately, coal has its industrial uses. Steel is almost completely dependent on coal for production, and, cement for concrete is frequently produced with coal. Fortunately, it looks like solar furnaces (anyone else remember the first really big one in France? Web Link are going to make a comeback. The new company "Heliogen" seems to have a new system running that will be big enough, hot enough, and cheap enough to be an affordable replacement for coal. Web Link

>> Also, the numbers you cite for gas do not include the methane leaks, which are significant. We need to keep all this stuff in the ground.

Agreed. The fraction of methane lost in the supply chain is probably about 1/2 of a percent. That is a lot, given how potent methane is as a GHG, the GHG contribution is significantly greater than the "ton" estimate. I posted that chart mainly for people to see how much more carbon there is coal per BTU. I'm definitely in favor of phasing out all fossil fuels.

Unfortunately, a lot of people feel that cheap energy is a moral issue. e.g. Higher fuel prices have been the biggest driver for the "yellow vest" movement in France (helped along by foreign interference of course).

Posted by Steven Nelson, a resident of Mountain View,
on Dec 7, 2019 at 12:57 pm

hum - the Methane to BTU example (how much CO2) only makes sense for things like gas turbine electric generation / not home heating using an efficient heat pump. You operate at a low-enough temperature differential (moving heat from outside Palo Alto air to inside your house air) they operate at much higher efficiency that 'just burning it.'

Thanks Shelly for doing the Math/Science in a well formed instructional session! With the small percentage Methane transport loss to the atmosphere - it should be possible to wing-it and calculate the equivalent CO2 values. I'm afraid 'fracking production' of Methane may have a much sloppier leak-at-the-production field than old style production.

$40 per ton carbon tax! YES best to start there / than the $0 per ton that we have now.

Posted by Sherry Listgarten, a Almanac Online blogger,
on Dec 8, 2019 at 9:29 am

Sherry Listgarten is a registered user.

@Steven -- Great points. I've seen a number of writeups indicating that fracking may be related to the increased methane emissions over the last decade or so. Some examples are here and here.

Regarding a carbon tax, the initial price matters, but it's important to also pay attention to the way the price changes over time. For example, one of the most aggressive I've seen starts at $10, but ratchets up by $10 each year, and goes up even faster if emissions are not decreasing fast enough.

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