There is a common myth about volcanoes being spouted about by armchair experts across the intertubes, and it's spreading like wildfire. Many well-educated people simply accept this myth as fact, because at face value, it seems perfectly reasonable. The myth I'm talking about is that volcanoes produce more carbon dioxide than people do and, because of this, that humans have very little impact on CO2 levels. Reality, it seems, disagrees.
Who am I to challenge this convention of modern wisdom? In this case, I am no one special. I hold no advanced degrees in nor am I an expert in volcanology, climate, chemistry, or anything related to this post for that matter. The only difference between me and the armchair experts who spout this myth as gospel is that I actually took the time to research this myself before taking a stance on the issue. So please, follow along. The math is all simple grade school level multiplication and division. I've listed my sources at the bottom of the post if you feel like following up on things.
Now, on to the numbers...
In 2003, the Bureau of Transportation Statistics reported that out of about 107 million U.S. households, each had an average of 1.9 cars, trucks or sport utility vehicles and 1.8 drivers. That comes out to about 204 million vehicles and 191 million drivers. (See source 1)
So, if an average driver drives 12,000 miles/year, what is the average amount of CO2 emitted by an average US driver?
Well, based on based on 23.9 mpg average, passenger cars emit an average of 13,028 pounds of co2/year which equals about 5.9 metric tons/year. Light trucks, which include SUVs, emit an average of 17,626 pounds of co2/year which equals about 7.995 metric tons/year, based on an average of 17.4 mpg. (See source 2)
So, to be conservative, we'll take the number of drivers (in 2003) and multiply it by the average of the average emissions of cars and the average emissions of light trucks.
191 million drivers x (5.9 + 7.995)/2 metric tons of co2/year = 191 million drivers x 6.9475 tons of co2/year = 1,326,972,500 metric tons of co2 per year in the US.
It should be noted that this does not include the more heavily populated regions on Earth such as China and India. This also does not include average amount of CO2 released by power plants, airplanes, heavy trucks, trains, and industry.
Now for the volcano data:
Average amount of CO2 released by volcanoes/year: 110 million tons. (Source 3)
Now... Is it just me, or is 1,326,972,500 tons slightly larger than 110,000,000 tons?
Well, let's check. First off, is the volcanic tonnage metric or imperial? The source didn't say, so we'll go both ways just to be sure.
If the volcanic tonnage is metric, then we simply divide 1,326,972,500 metric tons by 110,000,000 metric tons. The results show that, in 2003, the US was emitting more than 12 times the average amount of CO2 released by volcanoes.
Now, let’s say that the volcanic tonnage was imperial. First, let’s convert our known metric tonnage to imperial tonnage: 1,326,972,500 metric tons = 1,306,015,000 imperial tons. Now, let’s divide that by 110,000,000 tons. 1,306,015,000/110,000,000 ≈ 11.87.
The results are clear. Even with imperial tonnage, the US, back in '03, still emitted close to 12 times the average CO2 released by volcanoes/year.
Now that we have the results, does this mean that humans are having an effect on global warming? That is uncertain, and remains a hot topic of debate and is outside the scope of this post.
So, if we don't know if humans are causing/helping/accelerating global warming for sure, then what do we know?
Well, if CO2 emissions are tied into the causes of global warming, then the population of the US alone is emitting at least 12 times more CO2/year on average than volcanoes do. So, IF, and I mean IF, CO2 is causing/helping/accelerating global warming, then humans that live in the United States alone have, on average, 12 times more impact on global warming than nature does through volcanoes.
Again, it should be noted that this does not include the more heavily populated regions on Earth such as China and India. This also does not include average amount of CO2 released by power plants, airplanes, heavy trucks, trains, and industry.
Basically, the argument that humans don't emit as much CO2 as volcanoes is completely false.
I pulled this together with information from what I believe to be credible sources. I personally have no way of knowing the accuracy of this information, but I trust the sources since I consider the US Environmental Protection Agency, the USA Today, the Associated Press, US department of Transportation, and the San Diego State University's Department of Geological Science to be credible sources of information.
Calculations were conducted using the Windows calculator. Unit conversions were calculated by Google's calculator.
Update (7/25/07):
I originally wrote this sometime last year. It seems that the EPA’s page has altered their calculator and, in the interest of fairness and accuracy, I will post updated calculations using their most recent figures:
Amount of CO2 from car with 23.9 MPG and 12,000 miles/year:
10,654 pounds (4.83257311 metric tons)
Amount of CO2 from light truck with 17.4 MPG and 12,000 miles/year:
14,415 pounds (6.53853401 metric tons)
(source 2 and Google calculator.)
Average CO2: (4.83257311 + 6.53853401)/2 = 5.68555356 metric tons.
191 Million Drivers * 5.68555356 metric tons = 1,085,940,729.96 metric tons
1,085,940,729.96 metric tons ≈ 1,068,789,960 imperial tons
1,085,940,729.96 metric tons / 110,000,000 metric tons ≈ 9.872
1,068,789,960 imperial tons / 110,000,000 imperial tons ≈ 9.716
With the new updated figures, it comes out to nearly 10 times the amount of CO2 released by volcanoes.
However, the difference in calculations could be attributed to more efficient cars and/or tougher emissions standards placed on auto makers. Even so, the numbers still prove that, back in 2003, the total CO2 released by cars, light trucks, and sport utility vehicles in the US alone still eclipses the amount of CO2 released by volcanoes by a factor of 10!
Source 1: href="http://www.usatoday.com/news/nation/2003-08-30-outnumbered-cars_x.htm
Source 2: http://yosemite.epa.gov/oar/globalwarming.nsf/content/ResourceCenterToolsGHGCalculator.html
Source 3: http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html
