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How much carbon dioxide does a typical SUV release into the atmosphere, and how many trees does it take to absorb all that CO2? The answer is anybody's guess, but here's my take on it:
One gallon of gasoline weighs about 6.2 lbs. Of that, over 5 lbs. is carbon and the rest is hydrogen. The EPA says that burning one gallon of gasoline produces about 19.4 pounds of CO2. The carbon atoms in the gasoline combine with about 14 lbs. of oxygen atoms from the atmosphere when the fuel burns to yield 19.4 pounds of CO2. Additional oxygen from the atmosphere also combines with the hydrogen atoms in the fuel to produce about 8.5 lbs. of water vapor (H2O, which is equivalent to about a gallon of water.If a typical SUV gets 17 mpg in city driving (according to EPA's estimates) and is driven 12,400 miles a year (average miles driven in 2001, again according to EPA figures), it will burn 729 gallons of gas. That puts 14,142 lbs. of carbon into the atmosphere (combined with oxygen as CO2).
A mature tree 40 to 50 feet high weighs around 10,000 lbs. Of that, at least 7,000 lbs. is organic carbon compounds (the exact amount will vary depending on the species and the density of the wood). To reach this size, most trees need 30 to 40 years of growing time. This too will vary depending on the species of tree, its geographical location, soil conditions and weather. Trees in hot, wet tropical climates grow a lot faster than trees in northern climates.
Assuming these estimates are reasonably accurate, one mature tree contains about as much carbon as the exhaust fumes from a typical SUV in a year. But remember it takes 30 to 40 years for the tree to absorb all that carbon from the atmosphere. Photosynthesis takes time. It doesn't happen overnight. In fact, leaves use sunlight and water during the daytime only to convert CO2 from the atmosphere into tree sap (glucose) that the tree then uses to grow and build more wood fiber. The tree's average carbon uptake, therefore, may only be about 200 lbs. of carbon a year.
To offset the carbon released by driving a gas-guzzling SUV 12,000 to 15,000 miles a year, therefore, it probably takes at least 35 medium-sized healthy trees to convert CO2 into wood.
The carbon that is pulled out of the atmosphere by the trees stays bound up in the wood until the tree dies, is chopped down or burns. If a tree dies of old age or is blown down in a storm, the wood slowly rots. Some of the carbon is slowly released back into the atmosphere as CO2 during decomposition, but some of it is also converted into organic compounds that remain in the soil as nutrients for other plants, fungi, worms and insects.
If the tree is cut down and made into lumber, the carbon also stays bound up in the lumber until something happens to whatever the lumber was used to build. But if the tree is destroyed in a forest fire, is burned to clear land or is cut for firewood, all of the carbon that's been stored in the tree since it was a sapling is immediately released back into the atmosphere as CO2 when the wood burns. Consequently, burning a tree is the carbon equivalent of driving a gas-guzzling SUV 15,000 miles a year.
Here's another fact to ponder. Every time a farmer in a Third World country clears and burns an acre of heavily wooded forest to grow sweet potatoes or graze cattle (a practice called "slash and burn" agriculture), he releases as much carbon into the atmosphere as 400 SUVs do in a year! And many of these farmers will slash and burn 20 to 50 acres a year!
In Brazil alone, nearly 3 million acres of rain forest are being slashed and burned into oblivion every year. Multiply these acres times the amount of carbon that is being put back into the atmosphere and it far outweighs the CO2 that's being released by the entire U.S vehicle fleet! So don't pin all the blame for Global Warming and Climate Change on SUVs, cars and trucks. Blame deforestation, industrialization and cow farts (which release methane, which is a greenhouse gas).
Cars and trucks today run cleaner than ever before, and the newest models are getting better fuel economy. However, that does not mean the automotive industry does not face some serious environmental challenges.
Today's emission controls have done an amazing job of minimizing pollution from motor vehicles. But one thing emission control technology has not been able to change is the basic chemistry of combustion itself. The ongoing issue is CO2 (carbon dioxide) and the impact rising levels of atmospheric CO2 worldwide is having on the climate. Rising CO2 levels cause a gradual warming of the Earth's average temperature. This can change ocean temperatures, currents, global weather patterns and rainfall, all of which can have far-reaching and negative consequences for agriculture, fishing and life in general. Some fear it may even lead to a melting of the polar ice caps causing the oceans to rise and flood coastal areas.
To reduce CO2 emissions, we should be switching to smaller, more fuel-efficient cars, hybrid vehicles and plug-in electric vehicles. But the trend has actually been in the opposite direction as more and more Americans opt to buy larger Sport Utility Vehicles and Crossover vehicles. Fuel economy requirements for trucks have improved, but not enough to offset the change in consumer buying habits. And hybrid sales account for less than 3 percent of all new vehicle sales.
FUTURE CONSEQUENCES?
We now have more motor vehicles than
licensed drivers in this country (268 million vehicles as of 2017). The worldwide vehicle
fleet is now in excess of 1 billion cars and trucks, up from a mere 50
million in 1950! What's more, the world vehicle population is growing at an average rate of 4.6 percent a year, mostly in Asia and China. All of these
vehicles will add millions of tons of CO2 as a byproduct of
burning gasoline and diesel fuel.
With fewer trees left to absorb carbon and more vehicles producing carbon, don't expect the atmosphere's carbon balance to improve any time soon. The scales have probably tipped irreversibly towards higher and higher levels of CO2 for the foreseeable future.
Nobody argues with the fact that the amount of CO2 in the atmosphere is steadily rising because of human activity. In Al Gore's documentary, "An Inconvenient Truth", he quotes a lot of scary statistics about what's happening with the earth's climate as a result of rising levels of CO2 in the atmosphere (I HIGHLY recommend watching this movie whether you believe rising levels of CO2 are causing climate change or not.). What we don't know is what the long-term consequences of a CO2 imbalance will be or how it will actually affect our daily lives. Waiting to find out may prove costly if we miss the window of opportunity to make significant changes now.
Many environmentalists say one step we can take now to reduce CO2 emissions is to improve the fuel economy of all classes of vehicles. U.S. fuel economy standards has more than doubled since the energy crisis days of 1973, but is only about 22 to 24 mpg for light duty trucks (which includes most SUVs). Passenger cars are much better with an average fuel economy rating of 37 mpg for 2018.
According to the Sierra Club, every day America consumes 18 million barrels of oil. Not all of that is for transportation, but in a year's time we burn up about 120 billion gallons of gasoline.
If light trucks and SUVs could get the same mileage as passenge3r cars (which they can't because of their larger size and weight), it could save one million barrels of oil per day. That's a lot of carbon! Raising the CAFE standards for cars to 45 mpg and light trucks to 34 mpg would increase the savings to three million barrels of oil per day.
Rising fuel prices rather than Congressional action (or inaction as is usually the case) would provide the strongest incentive to get motorists to buy more fuel-efficient vehicles and reduce their driving. In recent years, fuel prices have remained below $3 a gallon for both gasoline and diesel. But it's hard to cut back on the number of miles driven (we drive over two trillion miles a year now) because our cities and suburbs are sprawled out. Most people are totally dependent on a motor vehicle to get to work, school, to shop and do everything else in life (thankfully for those of us in the parts and service business). Mass transit doesn't work outside the central cities because things are too spread out (thank you urban sprawl). And in rural America, a car or a truck is the only way to get to town or any place else.
Depending on how the control strategy is set up, a hybrid-electric may deliver double the fuel economy of a conventional vehicle in normal driving, and it may even triple the usual mileage in urban stop-and-go driving. Instead of wasting fuel at a stoplight, a hybrid-electric shuts the engine off when the vehicle stops. The engine remains off until the light changes and the vehicle accelerates on battery power up to a certain speed.
Another approach that can save fuel without sacrificing performance is to use a turbocharger with a smaller displacement engine. The current trend in light trucks is to turbocharger a V6 so it delivers power equivalent to a V8 but with better fuel economy and less CO2 in the tailpipe.
Many new vehicles are also being equipped with Idle Stop/Start systems that shut off the engine when the vehicle is sitting at a stop light to save fuel.
Hybrid electric vehicles and plug-in electrics can also reduce fuel consumption and CO2 emissions significantly. But unless there is a large-scale shift to these vehicles (and at prices the average consumer can afford), they won't have a big impact on fossil fuel consumption or CO2 emissions.
Electric vehicles are the cleanest of all, but are only available in limited numbers. Electric vehicles emit no pollutants or CO2, which helps improve air quality in urban areas. They're the ultimate energy-efficient vehicles for stop-and-go driving because they waste no energy when they're stopped in traffic.
There's also the issue of whether or not electric vehicles would actually reduce pollution. The electricity needed to recharge the battery has to come from another power source. Unless that power source is nuclear, hydroelectric, wind, solar or geothermal, there is little or no net reduction in pollution or CO2 because most electrical power in this country is generated by burning coal or natural gas. No new nuclear power plants have been built in the U.S. for over 25 years, and many nukes are now reaching retirement age and will have to be decommissioned. Unless there is a rebirth of nuclear energy or a large-scale shift to alternative sources of clean power (which are more expensive and require huge financial investments), the future doesn't seem very bright for electric vehicles, either.
So far, Tesla is the only vehicle manufacturer that has successfully produced electric vehicles that people actually want. They are great cars, fun to drive and have driving ranges of 200 to 300-plus miles. But they also have high sticker prices that most working class people can't afford. So until the price comes down, they will remain status symbols for the rich.
Even with an advanced battery breakthrough, some question whether the existing power infrastructure has the capacity to supply the needs of an expanding fleet of electrical vehicles. Some experts say the U.S has enough excess generating capacity to power up to 80 percent of the vehicle fleet if they were all electric or plug-in electric-hybrids.
Hydrogen Fuel Cells hold the greatest promise for solving our environmental concerns over pollution and CO2. A fuel cell produces electricity by combining hydrogen and oxygen. The only byproduct is water vapor - provided the fuel source is pure hydrogen.
Hydrogen is one of the most abundant elements on Earth. It can be made from natural gas, oil or even coal or by using electricity to break down water into hydrogen and oxygen. Even so, it's not cheap to produce and contains less energy than hydrocarbon fuels.
Hydrogen is also a hard-to-store fuel. Because it's a gas, it has to be compressed at extremely high pressure (3,000 to 4,800 psi). This requires large, heavy, expensive fuel tanks that reduce a vehicle's driving range and fuel economy. It can be liquefied to increase its storage density, but this requires special insulated cryogenic storage tanks to keep the fuel at -253 degrees C.
Another storage method is to use "metal hydrides" or activated carbon that can absorb hydrogen like a sponge. But these approaches are also bulky, heavy and expensive. What's more, there is no distribution system for hydrogen like there is for gasoline, diesel fuel or even natural gas. So even if you had a hydrogen-powered vehicle, you'd have a hard time finding a place to fill it up.
One solution for storing hydrogen is to not store it as a gas but to extract it from another fuel such as gasoline or methanol alcohol. A device known as a "reformer" can break down these fuels to release the hydrogen. But adding a reformer adds cost and complexity, and also reduces its fuel efficiency. Even so, DaimlerChrysler, Mercedes, BMW and several other vehicle manufacturers have all demonstrated prototype fuel cell powered vehicles that use reformers to extract hydrogen from gasoline or methanol.
Why not just burn hydrogen in an internal combustion engine and forget the high-tech fuel cell and reformer? You can, but compared to other fuels, hydrogen is a lousy motor fuel. It has a very low octane number, which means it causes detonation and pre-ignition unless the compression ratio is cut way down. It also tends to backfire through the intake manifold. And it doesn't get very good fuel mileage, either. A gallon of liquefied hydrogen has only about one-fourth the energy content of a gallon of gasoline.
Time will tell which technologies will eventually help us meet our environmental challenges. It's not just motor vehicles that bear the brunt of reducing pollution and CO2 emissions. It's all forms of energy consumption and power generation worldwide as well as the issue of deforestation. Hopefully, we can come up with solutions that satisfy everybody's concerns and needs while there is still time.
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