On 7 December, when I wrote the blog below, we were experiencing a warm wind called a “Chinook” here in Boulder, Colorado. I wanted to wait until after the surface temperature field campaign to post this. It seems appropriate to do so this morning (30 December), since we are again experiencing a Chinook, and this blog was designed to follow the second birding blog. Winds have gusted to over 100 kilometers per hour, and the temperature outside is 12 degrees Celsius – quite warm for an early morning in December! During a Chinook, the temperature warms rapidly. Chinooks are also called “snow eaters” because they can make winter snows disappear quickly. They can also make the temperature rise suddenly by tens of degrees.

In my last blog on birding, I took a picture of a blind on Saturday, 6 December (Figure 1). Early that morning, the temperature was cold (about -5 degrees Celsius) and the ground had about 12 centimeters of snow on the ground. The lakes near the blind were frozen when we arrived there around 9:30 a.m. local time. The temperature was probably still below freezing when I took the picture. The next morning, we woke up to 10 degree Celsius temperatures, and the 12 centimeters of snow we had in our yard had entirely disappeared. When we returned to the blind to record the how different things looked, it was 11:30 a.m. local time – about 26 hours later.

Figure 1. Picture of blind taken for last blog. Sawhill Ponds, Boulder, Colorado, 10:00 a.m. Local time. The snow was about 10 centimeters deep here; the lakes were frozen.

Figure 2. Picture of blind, roughly 26 hours later (11:30 Local Time, 7 December 2008). Note that not only has the snow disappeared, but the soil is dry in some places.

Basically the temperature didn’t fall much the night of 6 December – in fact it might have even warmed. This is because air is coming down from higher up in a Chinook. As air sinks in the atmosphere, it gets compressed (squashed) by having more air above it pressing down. This squashing warms the temperature – much as the temperature of the air in your bicycle tire warms when you pump (squeeze) more air into it. In sinking dry air, the temperature rises 10 degrees Celsius for each kilometer – quite a bit.

Figure 3 shows the temperature record for another Chinook (the instruments at NCAR Foothills Lab, which lies between where we live and Sawhill Ponds) weren’t working on 6-7 December, so I couldn’t get the data). The air is very dry during the Chinook. (The air is dry if the temperature is much higher than the dew point. Recall that fog or dew forms when the temperature and dew point are equal, so it makes sense that drier air has lower dew points). The dryness of the air is not surprising – the air is drier higher up. So the dryness is a sign that the air is coming from higher up.

Figure 3. Temperature and dew point from a Chinook on 11 February 2008, at roof level. From NCAR Foothills Laboratory in Boulder, Colorado. You can tell from the cooler temperatures starting around 15:00 local time that the Chinook ended about that time. From http://www.rap.ucar.edu/weather/.

You notice how the temperature went up half way between 23:40 (11:40 p.m.) and 02:40 (2:40 a.m.) local time and then didn’t change much for the rest of the night like it normally does? Also the temperature wasn’t going up much the next morning. (Note: 50 degrees Fahrenheit is about 10 degrees Celsius). During this time the wind was out of the west – from the mountains, meaning sinking air (Figure 4). Also notice that the temperature cools off when the wind changes from west to north at around 15:00 local time (3:00 p.m.).

Figure 4. As in Figure 3, but for wind direction

The lack of a temperature change makes me think that the air in Boulder didn’t just simply slide down the mountain, but we were getting air from above the surface. Air high above the ground doesn’t cool or warm as much as air right next to the ground does.

So we have four clues that the air came from higher up during the Chinook. First, the temperature rose to abnormally high levels at the onset of the Chinook and rapidly cooled afterward. Second, the wind came from the mountains to the west. Third, the air was very dry. And finally, the temperature didn’t change during the day like it normally does. The last clue also suggests the air came from above the surface.

What do the clouds look like? In a Chinook, the wind blowing across the mountains flows in ripples much like the water flows over rocks in a stream. It’s harder to see air flow than to see the water flow. However, clouds occur when the air is at the top of ripples, if the air is moist enough. From the surface here in Boulder, we saw a long line of low clouds stretching along the mountains (one ripple), and higher cloud doing the same thing, but farther east (Figure 5).

Figure 5. Clouds associated with the Chinook at 14:50 local time, looking northwest. The mountains are to the west. The cumulus clouds near the horizon are just to the east of the mountains, which are not visible on this picture. The higher clouds (altocumulus) are part of a broad north-south band starting east of the mountains. The little tail in the middle is the leftovers from a contrail. Looking eastward, I could see that the altocumulus clouds stretched to the horizon.

You can probably see this more clearly from space. First, I show you the visible image (Figure 6). You can see some ripples over the mountains, a dark area stretching from Boulder (plus sign) to the south, and the altocumulus (or higher) clouds extending east-south east from the dark area.

Figure 6. GOES satellite visible image of clouds at 2132 UTC (1432 Local Standard Time). The plus sign snows where Boulder is. Note the north-south clouds along the Rockies in the middle of Colorado (like ripples in the water). Then there is a broad band of clouds stretching eastward to the east side of Colorado. This is the larger-scale view of the altocumulus in Figure 5. From http://www.rap.ucar.edu/weather/satellite/.

We can see the difference in the heights of the “ripples” and the broad area of altocumulus clouds by looking at the image showing the infrared signal (Figure 7), which is related to the temperature the satellite “sees” – either at the surface or at the top of the clouds. Since the temperature in the atmosphere drops with height at these heights, this temperature can be used to estimate cloud top height. The brighter areas indicate higher cloud tops, so the broad band of clouds to the east of Boulder appear to be higher than the ripples, which are hard to see.

Figure 7. GOES satellite infrared image in and around Colorado at 2132 UTC (1432 local time). The plus sign shows where Boulder is. The broad bands of clouds are showing up much more than the ripples. Since lighter colors indicate higher clouds, this tells us that the broad area of clouds to the east is higher than the ripples – just as in the picture I took in Boulder. (But I’m not sure we can see the ripple in my picture on the satellite). From http://www.rap.ucar.edu/weather/satellite/.

What was the result of the Chinook? We already pointed out the much warmer temperatures, the complete melting of our snow (12 cm in our yard originally), and the melting of ice on many of the lakes.

This also affected the ducks in the lakes near the blind.

On 6 December, when we went out to photograph the blind, we could find no ducks on the frozen ponds – only Canada geese waddling on the ice. Also, there were almost no birds at the feeders in our back yard. We were surprised, because we thought they would be hungry in the cold weather.

On 7 December, when we got up, the feeders were full of birds. So were the trees: chickadees, pine siskins, sparrows, finches, juncos, and collared doves, were eating continuously, even when squirrels and cats (and in one case a deer with antlers) came by. Today, when we went back to Walden Ponds (north of the blind), we saw many ducks on the one pond that had thawed out most completely. And the ducks and geese were eating. My guess is that they were making up for yesterday. But – there is a mystery. Where were the ducks during the cold weather? What do you think?

Do you have names for winds where you live? Winds – particularly those that bring different weather – have names around the world. In Africa, the hot dry winds that come south from the Sahara are called Harmattans. In southern Europe, cold winds that come out of the mountains are called Boras and warm winds that come out of the mountains are called Foehns in Germany. However, we also use the word “foehn” to describe warm dry winds from the mountains in the United States. In South Africa, the warm winds coming from the mountains are called “berg winds,” since “berg” means mountain in Afrikaans. There is no snow to melt, but the berg winds do raise the temperature in winter.

Understanding something as complicated as climate change is really tough. So it’s easy to understand why people don’t always get things right. But it’s much easier to explain why the term “global warming” is misleading than it is to explain why some climate-change messages are only partially understood. So I put the “partial misconceptions” in a separate blog.

Partial Misconception: The greenhouse warming is due to carbon dioxide. Figure 4 shows that slightly over half of the warming near Earth’s surface is caused by carbon dioxide (CO2), with other gases – methane (CH4), Nitric oxide (N2O), halocarbons, and ozone in the lower atmosphere, accounting for the rest of the “forcing.” What is forcing? Forcing can be thought of as a “push” that warms (or cools) the Earth system.

The warming that results is actually larger then you might expect from an increase in these gases alone. This is because the warming surface and air leads to more water vapor, which is also a greenhouse gas. This leads us to the next partial misconception.

Figure 4. Effect of greenhouse gases and aerosols on surface air temperature warming, in terms of “forcings.” From 2007 report, Intergovernmental Panel on Climate Change.

Misconception: Carbon dioxide is the most important greenhouse gas. Certainly this is what you might expect from a first glance of Figure 4. But where is water vapor? I was taught as an Atmospheric Science graduate student that water vapor was the primary greenhouse gas, but carbon dioxide was also important. Modeling studies with various degrees of simplification confirm this first impression. A nice summary can be found on the RealClimate blog.

Why, then, do so many people say that carbon dioxide is the “most important greenhouse gas.” It’s probably because of figures like Figure 4. Note a very important adjective at the bottom which is often ignored, “anthropogenic,” meaning “made by humans.” Humans of course affect water vapor as well, but it cycles through very fast, and the amount of water vapor in the air is basically controlled by the temperature of the air and surface. In a climate model, water vapor continuously adjusts to the conditions within the model, while anthropogenic greenhouse gases in Figure 4 are adjusted by those who run the model.

Put another way, water vapor doesn’t appear in the “forcing” terms for climate models, because it is “internal” to the system. It changes as the result of a “feedback” within the model. Thus external inputs like solar radiation, changes in ground cover, and gases introduced into the atmosphere by human activity are counted as “forcing” but water vapor as not.

In short, we can say that carbon dioxide is the most important greenhouse gas whose amount people are directly altering. Not just in models, but in real life.

Partial Misconception: The warming climate means more exposure to dangerous diseases. I say “partial misconception” because there are multiple factors that change our exposure to disease. Many articles in scientific journals and newspapers discuss increased exposure to malaria, for example, in a warming climate. But that is not the whole story. For example, in the United States, malaria was a real threat over much of the country in the 1700s and the 1800s, and even into the early 20th century. However, public health efforts such as mosquito control and changes in peoples’ habits (for example, using window screens to keep out mosquitoes or staying indoors from dusk to dawn) have largely removed the malaria threat. Similarly, world travel spreads germs, such as the West Nile virus, around the world. This is not a new phenomenon. Europeans coming to the Americas brought small pox with them, leading to the tragic death of countless Native Americans. And populations moving into new areas can expose themselves to new germs.

However, we cannot ignore the fact that vectors for existing diseases will migrate with their preferred climate. Thus at some time in the future, some diseases will show up in areas where they haven’t been before; and in other areas where they have been suppressed.

Partial misconception: The warming climate means more birds will die. Again, there are many factors involved. There are stories of bird populations suffering because food supplies (for example caterpillars) are no longer available when the birds need them, because the two species are responding differently to climate change. However, songbird populations have also suffered because the scarcity of predators like wolves has led to an increase in the number of animals (like raccoons) who eat birds’ eggs. Similarly, pesticides have done serious harm to bird populations. This contributed to a ban on the use of the insecticide DDT in many countries. Finally, the West Nile virus has led to the deaths of many birds (although the magpies and crows, which fell victim to West Nile, seem to be recovering here in Boulder).

Once again, we cannot ignore the impact of climate change. If climate changes continue at the predicted rates, then the entire ecosystem will have to adjust to a new seasonal cycle. This will not be a smooth process: different plants and animals will respond in different ways. And, as in the case of the birds and caterpillars, the food supply will be interrupted at critical times.

Partial Misconception: If we cut back on our production of greenhouse gases, global warming will “go away.” This is true only over a very long period of time. It will take hundreds of years to decrease the carbon dioxide content back to pre-industrial levels through natural processes (the lifetime of carbon dioxide in the atmosphere is around 120 years). This does not mean we shouldn’t consider reducing carbon-dioxide emissions, because continuing the increase in carbon dioxide leads to even more warming than if we slow down the increase in carbon dioxide. One hopeful note is that not all greenhouse gases last as long as carbon dioxide, so reducing their release in the atmosphere might help on shorter time scales. Another hopeful note is that people are studying ways to take carbon dioxide out of the atmosphere, but this is the subject of another blog.

So, when you read or hear about the effects of people on the environment, or try to figure out what you can do to help the environment, please remember that we affect our environments in many ways. Similarly, actions we take to help our environment can improve our environment in many ways. But responding to climate change will remain a challenge for years to come.

The amount of CO2 given off by industry in a year

Figure 1 is a diagram of the carbon cycle from the GLOBE Carbon Cycle Project, based at the University of New Hampshire. This diagram shows where the carbon is, and where it is going. So, for example, industry produces about 6 petagrams of carbon a year. What is a petagram? A petagram is written 1,000,000,000,000,000 grams, which can be written 1 times 10^15.

In order to compare the value of CO2 production for human respiration to the “flux” or exchange terms in the diagram (in red), we have to (a) convert it to a flux for carbon rather than CO2 and (b) compute a total for the entire world population for a year.

So, we take

0.9 kg per person per day, times
6,700,000,000 people in the world, times
365 days in a year (neglecting leap years), to get
220,000,000,000 or 2.2 x 10^11 kg or 2.2 x 10^14 grams, or

0.22 petagrams

To convert this to carbon, we multiply by 12/44, the fraction of CO2 that is carbon, to obtain 0.06 petagrams a year.

From Figure 1, that’s about 1% of most of the exchange terms, and about one-hundredth the carbon released by burning fossil fuels globally. And less than one-thousandth the amount of carbon uptake by plants.

What does this really mean? It was pointed out to me by Richard Wolfson, a professor of physics at Middlebury College [who wrote the book Energy, Environment, and Climate (W.W. Norton, 2008), cited a few blogs ago.], that we get our energy from plants, or animals that eat plants, or animals that eat animals that eat plants, so one could argue that we are “carbon-neutral” in the sense that we are part of the natural system, with the plants taking back the carbon we emit. Only in a sense, however – as Wolfson notes, our food production is not carbon-neutral: we produce carbon dioxide in growing the food and transporting the food, not to mention keeping it warm or cold, and, usually, cooking it.

Figure 1. The carbon cycle. The numbers in blue in represent the amount of carbon stored (e.g., 38,000 petagrams of Carbon in the ocean). The numbers in red represent “fluxes” – carbon flowing from one part of the earth system to another. Figure © GLOBE Carbon Cycle.

CO2 from Space

Figure 2 is a snapshot of the global distribution of CO2 at 8 kilometers (5 miles) above the surface. This is high enough so that there is a lot of mixing by the winds, but you can see a pattern anyway. And the pattern is associated with the sources and sinks of carbon in Figure 1.

Figure 2. July 2003 average CO2 from the Atmospheric Infrared Sounder (AIRS) on the Aqua Satellite. From http://www-airs.jpl.nasa.gov/Products/CarbonDioxide/. Preliminary data.

For example, the higher values are associated with the industrial parts of the world. The high values in the north Atlantic are downstream from the United States and Canada. The lowest values are over the high-latitude oceans in the Southern Hemisphere and over Antarctica.

Figure 3. CO2 from AIRS. From http://www-airs.jpl.nasa.gov/Products/CarbonDioxide. Preliminary data. The curve shows carbon dioxide decreasing in the Northern Hemisphere spring and summer, when vegetation is growing and leafing out, and increasing in fall and winter, when respiration dominates.

The “snapshot” in Figure 2 is from the Atmosphere Infrared Sounder (AIRS) on the NASA/Aqua satellite. These data can also be used to look at trends in the global average CO2. Like the well-known surface-based curve from Mauna Loa, there is an upward trend, and you can clearly see the effect of the seasons. If you compare this figure to the curves in the blog Land Use and CO2, posted 7 September 2007, you will find the curves quite similar, with CO2 decreasing during the Northern Hemisphere spring and summer. As noted there, this decrease in carbon dioxide is associated with photosynthesis. During photosynthesis the plants take carbon dioxide out of the atmosphere and use it to grow and leaf out. It is not surprising that photosynthesis is the largest term in Figure 1.

The blog about carbon dioxide (CO2) produced by our bodies during respiration created so much discussion that I decided to work harder to put the numbers into context.

Last time, we calculated an average adult human breathes out between 0.7 and 0.9 kg of carbon dioxide each day. This is based on lots of assumptions, with people of all ages and nationalities counted as processing 0.5 liters of air, 16 times an hour, for 24 hours.

Let’s compare this rough estimate to some other numbers.

The amount of carbon dioxide given off by an automobile in a mile (1.6 kilometers)

I’ve heard a number quoted for this one, but thought it would be good to estimate to find out how close I was, and then I will convert the number to metric units. We start from some facts.

• Density of gasoline is 0.71-0.77 grams per cubic centimeter (that’s 0.71-0.77 kg per liter)
• Gasoline is 85% carbon by mass

So there is approximately 0.74 times 0.85 = 0.63 kg carbon per liter.

This converts to 0.63 kg C x 3.79 liter/gallon or 2.39 kg C per gallon (C=Carbon).

If our car drives 20 miles on one gallon of gas (this is clearly not a very efficient car!), the car burns 2.39 kg per gallon x 1 gallon per 20 miles, or 0.12 kg of carbon per mile.

This is equivalent to 0.12 x 44 divided by 12 = 0.44 kg per mile, or 0.96 pounds (~1) pound of carbon dioxide per mile. Or, in metric units, 0.28 kg per kilometer.

And, driving this car for two miles (3.2 km) produces 0.88 kg carbon dioxide – as much as we produce by breathing all day! (What if the car could travel twice as far per gallon?)

Carbon dioxide released by going from Point A to Point B.

I’m going to suppose someone wants to travel two miles or 3.2 kilometers. That’s a distance many of us would be willing to walk (and about the distance between where I live and where I work).

That means:

If we walk three miles per hour, it would take us 40 minutes to reach Point B walking 3 miles an hour.

If we ride a bicycle at 8 miles (12.8 kilometers) per hour on average, it would take 15 minutes to get to Point B.
The Web is full of charts listing the number of Calories (kCal, abbreviated kCal) used in different types of exercise. I’ll select the following values. For a 155-pound (70 kg) person:

• Walking at 3 miles per hour (4.8 km/hr) burns 250 kCal
• Riding a bicycle at 8 miles per hour (12.8 kilometers per hour) burns 280 kCal

Which means the number kCal burned going from Point A to Point B is:

• 167 kCal walking for 40 minutes compared to 56 kCal for 40 minutes at rest
• 70 kCal riding a bicycle for 15 minutes compared to 21 kCal for 15 minutes at rest

The “at rest” numbers are based on the previous blog, where we used energy production to estimate carbon dioxide output. We assumed a human produced 2000 kCal of energy (equal to the amount eaten) and found that roughly equivalent to 0.7 kilograms of carbon dioxide a day. (0.9 kg a day could be used as well. We used 0.7 simply because that was the number associated with the 2000 kCal.

The carbon dioxide we produce by going two miles on foot or on a bicycle is then, if we count the total:

• 0.7 kg CO2 per 2000 kCal times 167 kCal: 0.058 kg CO2 walking
• 0.7 kg CO2 per 2000 kCal times 70 kCal: 0.025 kg CO2 biking

But the “extra cost” of traveling the distance should be the difference between the “exercising” number and the “at rest” number, namely:

• 0.7 kg per 2000 kCal times (167-56) kCal = 0.039 kg of extra CO2 walking
• 0.7 kg per 2000 kCal times (70-21) kCal = 0.017 kg of extra CO2 riding a bike

Thus: traveling the 2 miles (3.2 kilometers) produces this amount of CO2 above what was produced by respiration at rest:

Traveling 2 miles (3.2 kilometers)

By car: 0.88 kg CO2
Walking: 0.039 kg CO2
Riding a bike: 0.017 kg CO2

While the numbers aren’t exact, the large factor – 20 or more, is probably close. Walking or riding a bicycle does reduce the production of CO2 relative to driving. And – these modes of transportation provide healthful exercise as well! If we have to drive, putting more people in the car reduces the impact of driving. And, driving a car that uses half as much gasoline per unit distance would also help.

This blog was inspired by activities at the 2008 GLOBE Learning Expedition (GLE) in South Africa. As part of their field activities, the students visited the Global Atmosphere Watch station (GAWS) at Cape Point, where carbon dioxide and several other trace gases are measured from the top of a 30-m tower. The carbon dioxide record goes back to 1978, showing a rise comparable to that seen in the Northern Hemisphere.

Standing for much of two days with groups of students at the base of the weather tower at the GAWS site at Cape Point, I found myself wondering how much we were contributing to the carbon dioxide in the atmosphere. I returned home, resolving to estimate how much carbon dioxide an average human gives off in a given day simply by breathing.

Figure 1a. 30-meter tall Global Atmosphere Watch Station (GAWS) tower from a distance. It is located almost at the southern tip of Africa.

Figure 1b Close-up of GAWS tower. The air is pumped in from the top of the tower into the laboratory building, when it is analyzed for the fraction of carbon dioxide and other trace gases.

I will estimate this in two ways. First, based on how many Calories a “typical” human consumes. And secondly, based on how much carbon dioxide is released with each breath.

Based on how much we eat

I start with some rather gross assumptions:

1. The average human eats 2000 Calories (kiloCalories) of food a day
2. 100% of this food is processed, with all the carbon returning to the atmosphere
3. All of the food eaten is in the form of sugars with carbon:hydrogen:oxygen ratios of 1:2:1.

And some information:
Atomic weight of carbon: 12
Atomic weight of hydrogen: 1
Atomic weight of oxygen: 16
Molecular weight of carbon dioxide (2 x 16 + 12 = 44)

This means that:
By mass, the sugars are 40% carbon
By mass, carbon dioxide is 27% carbon

Sugar provides 4 kiloCalories of energy per gram, meaning that our human eats 500 grams of sugar each day. 40% of this or 200 grams is carbon. Assuming all this carbon is released as part of carbon dioxide, our human releases 733 grams of carbon dioxide (200 grams x 44/12).

So, let’s just call our estimate 700 grams of carbon dioxide a day, recognizing that the number is an approximate one.

There are a number of reasons this is probably an overestimate. Our human wouldn’t eat all sugar. He/she would eat some fat as well, which has 9 kiloCalories per gram. We are assuming our human to be in steady state – so that net uptake by the body would be zero. But our human would release carbon in other forms (feces, dried skin, shed hair, etc.) So there would be some solid waste as well as gas – but over long term, there would be some carbon dioxide released from that.

Based on carbon dioxide released through breathing (respiration)

Let’s try another way to estimate the amount of carbon dioxide our human releases. But this time we focus on breathing. Again, some facts:

A human adult breathes 15 times a minute, on average (Reference 1). While I am writing this, my respiration rate is 16 breaths per minute, so this number seems reasonable. And, just for fun, I’ll use my respiration rate.

Each breath exchanges 500 cubic centimeters of air (Reference 2)

Assuming an air density of 1 kilogram per cubic meter, we can find out how many kilograms of air are exchanged for each breath:

500 cm x cm x cm x 0.01 m/cm x 0.01 m/cm x 0.01 m/cm
= 0.0005 cubic meters

0.0005 cubic meters x 1 kilogram per cubic meter
= 0.0005 kilograms of air per breath.

We now use this to estimate the kilograms of air processed each day, which is

0.0005 kilograms per breath x 16 breaths per minute x 1440 minutes per day
= 11.52 kilograms per day “processed” by breathing

To find out how much carbon dioxide is put into the atmosphere, we compare the amount of carbon dioxide (0.038% by volume) inhaled to the amount (4.6-5.9% by volume exhaled, Reference 3.), from the same web site. But first we need to allow that “by volume” means (using carbon dioxide as an example)

0.038 carbon dioxide molecules per 100 air molecules, or
3.8 carbon dioxide molecules per 10000 air molecules.

From above, we know that the molecular weight for carbon dioxide is about 44. The molecular weight for moist air is about 28, which means that the air we inhale contains about

3.8 x 44 divided by 28 x 10000 = or 0.0006 grams carbon dioxide per gram of air

The number “.0006″ is really a fraction – which I am labeling in grams per gram. It could just as easily be pound per pound.

Similarly, the fractional amount of carbon dioxide exhaled, by mass is, assuming 5% by volume:

0.05 x 44 divided by 28 x 100 or 0.0786

So the net fractional change in carbon dioxide for each breath is

0.0786 – 0.0006 or 0.0.078

Now we convert this to a mass by multiplying the fraction times the mass per breath, namely:

11.52 kilograms of air exchanged each day x 0.078 fractional increase in carbon dioxide,

= 0.9 kilograms of carbon dioxide for each day per human.

Again, we made assumptions to make things simple. Our human wasn’t exercising. Our human was an adult. And our human was exchanging a typical amount of air. Recognizing that the number is a crude estimate, I will again round the number to one significant figure, so that we have 0.9 kilograms of carbon dioxide released each day per human.

Isn’t it exciting that we came up with roughly the same answer! For comparison, Wickipedia (http://en.wikipedia.org/wiki/Breathing) quotes an estimate of 900 grams of carbon dioxide a day by the United States Department of Agriculture (USDA).

Here are some questions to think about:

The respiration rate I used was for an average adult. When I measured my respiration, I was sitting, so I’m thinking this is for an average adult at rest. How would these numbers be changed for someone who was exercising? Children breathe faster (Reference 3) but have smaller lungs. How would each of these factors affect the result? Finally, if you wanted a more accurate number, how would you change the calculations?

Comparison to carbon dioxide uptake by plants

How does that compare to some other things?

Prairie near Mandan, ND during the growing season (24 Apr – 26 October) 1996-1999, (reference 4)
1.85 grams CO2 per square meter taken from the atmosphere on average
(Meaning that 380 square meters of land would cancel out the effect of our human) – but remember – this in only during the growing season!

A generic tree (reference 5)

This tree (I’m assuming this is a big one) is said to take up 21.8 kilograms of carbon dioxide a year. For a year, our human produces about 365 x 0.7 kilograms a year, or 255 kilograms. So we’d need 10 of these threes to cancel the carbon dioxide we exhale. This site unfortunately does not quote a source.

Pine forest in Finland (Reference 6)

During the period of measurement, this forest took up
2.4 grams carbon dioxide per square meter per day during July/August, and
1.7 grams carbon dioxide per square meter per day during September

In “human units”, taking 0.7 kg/day, this means we’d need
290 square meters to offset our exhaled carbon dioxide in July and August, and 410 square meters to offset our exhaled carbon dioxide in September.

So – we are part of the carbon cycle, too! At Cape Point, we were breathing out carbon dioxide, but the atmosphere sampled was 30 meters above us – so we probably did not affect the measurements there. But I hear stories from scientists who are measuring carbon dioxide uptake about how they avoid contaminating their measurements. Some of the things they do – push their cars when they get close to the instruments instead of driving them, and leaving their dogs inside the car instead of letting them wander around the site. For more about the carbon cycle, visit the carbon cycle pages on the GLOBE web site.

References

1. p. 151, Berkow, , R., et al., 1997: The Merck Manuel for Medical Information: Home Edition. Merck & Co, publishers, 1509 pp.

2. p. 44, Kapit, W., et al., 1987: The Physiology Coloring Book. HarperCollins. 154 pp.

3. The five percent was decided on based on several references. The Argonne National Laboratory “Ask a Scientist” (http://www.newton.dep.anl.gov/askasci/zoo00/zoo00065.htm) lists 5.3 per cent by volume for “alveolar air” in response to a question about how much CO2 is exhaled. This is slightly lower than the range of values for arterial blood gases derived from p. 907, Taylor, C., C. Lillis, and P. LeMone, 1989: Fundamentals of Nursing. J. B. Lippincott Company, Philadelphia. 1356 pp. On the other hand, http://en.wikipedia.org/wiki/Breath writes exhaled air has 4-5% carbon dioxide by volume, with the BBC listing 4%.

4. Frank, A.B., and A. Dugas, 2001: Carbon dioxide fluxes over a northern, semiarid. mixed-grass prairie. Agricultural and Forest Meteorology. 108, 317-326,

5. http://www.coloradotrees.org/benefits.htm#10

6. U. Rannik et al, 2002 fluxes of carbon dioxide and water vapour over Scots pine forest and clearing. Agricultural and Forest Meteorology, 111, 187-202

Acknowledgments. I talked about this blog a great deal with colleagues. I am indebted to Jimy Dudhia and Greg Holland for contributing useful ideas and information. Also, our sincere thanks to the staff at the Cape Point GAWS station for sharing their facility with the students at the GLE.