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SUV makes environmental impact

SUVs vs. Trees, CO2 Emissions & The Environment

Copyright 2001 AA1Car

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 (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 on SUVs, cars and trucks. Blame deforestation, industrialization and cow farts (which release methane, which is a greenhouse gas).

For information about planting trees to fight CO2 and global warming, Click Here.


Cars and trucks today run cleaner than ever before - but that does not mean the automotive industry does not face some serious environmental challenges.

The automotive industry has come a long way in its struggle to reduce pollution. Today's vehicles are the cleanest ever, and getting cleaner all the time. As the next levels of emission standards are phased in for cars, light trucks and heavy trucks, emissions will be reduced even more. Reduced sulfur content in fuels and "Tier II" emission regulations should lower vehicle emissions another 20-25 percent.

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 issue now is CO2 (carbon dioxide) and as CO2 levels continue to rise, scientists fear it will cause a gradual warming of the Earth's average temperature. This, they say, has the potential to upset ocean currents, global weather patterns and rainfall, which may 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 our CO2 emissions, we would have to drive smaller, more fuel-efficient cars, raise the fuel economy requirements for trucks, and adopt a variety of conservation measures to reduce energy consumption.

We now have more motor vehicles than licensed drivers in this country (210 million). The worldwide vehicle fleet is estimated to be about 430 million cars and trucks (up from 50 million in 1950), and will surpass 650 million within the next 8-10 years! Most of this growth is occurring in developing nations such as China that do not have the strict emission requirements that we do. And even if they do adopt the same emission standards as Europe, Japan and the U.S., all of these vehicles will still produce 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 have nearly doubled since the energy crisis days of 1973 - but have remained relatively flat at 27.5 mpg for passenger cars for the last 15 years. For trucks, the average fuel economy is only about 20 mpg. Yet because of the increased popularity of trucks and SUVs in recent years, the average fuel economy of all new vehicles in the U.S. has sunk to the lowest level since 1980!

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 the Corporate Average Fuel Economy (CAFE) standards for trucks were raised to match that of cars (27.5 mpg), 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 he case) will likely provide the strongest incentive to get motorists to buy more fuel-efficient vehicles and reduce their driving. 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.


hybrid vehicle

One solution that can allow us to keep our big SUVs and get good fuel economy too is "hybrid-electric" technology. With this approach, a small displacement, fuel-efficient gasoline or diesel engine is used in conjunction with an electric motor and battery to power the vehicle. The regular motor is used for highway driving and to charge the battery. The rest of the time the vehicle runs on electric power or a combination of battery and gasoline.

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.

As promising as this new technology is, there are currently only two vehicle manufacturers producing true hybrid-electric vehicles: Toyota and Honda. The Toyota Prius is a compact four-door car that has an EPA rating of 52 mpg in the city and 45 mpg on the highway. The domestic vehicle manufacturers currently sell a few "hybrids" that do little more than turn the engine off when the vehicle sits for more than a few seconds at a stop light. This saves a little fuel (maybe 1o to 15% depending on how much stop-and-go driving the vehicle does), but this type of hybrid does not have a full-electric mode of operation.

Unless there is a large-scale shift to mass-produced hybrid-electric vehicles, or diesels (more of which will be coming in 2008 and beyond), there will not be any significant improvement in CAFE numbers.

Electric vehicles are still on the fringe and will probably stay there because of lagging battery technology. Electric vehicles that emit no pollutants and no CO2 certainly make sense in polluted urban environments. They're the ultimate energy-efficient vehicles for stop-and-go driving because they waste no energy when they're stopped in traffic. But nobody has yet come up with a cheap, lightweight, safe, quickly rechargeable battery. And even if they did, it could take years for the new technology to go into mass production and for the public to accept it.

electric vehicles

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. GM already killed what could have been the first of many electric-powered cars (you should also see the documentary, "Who Killed the Electric Car?"

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. Yet some experts say the U.S has enough excess generating capacity to power up to 80% fo the vehicles on the road today if they were electric or plug-in electric-hybrids.


Hydrogen Fuel Cells currently 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.

Update 2007: Burning Palm Oil No Solution Either

In recent years, some power generating plants in Europe have been using palm oil as a substitute for petroleum because palm oil is a renewable biofuel that is carbon neutral, and it is relatively cheap. But a new report issued in late 2006 by Wetlands International, Delft Hydraulics and the Alterra Research Center of Wageningen University in Holland found that burning palm oil isn't such a great idea after all. The study measured the carbon released from peat swamps in Indonesia and Malaysia that had been drained and burned to plant palm oil trees. About 85 percent of the world's palm oil comes from the two countries, and about one-quarter of Indonesia's plantations are on drained peat bogs.

The four-year study found that 600 million tons of carbon dioxide seep into the air each year from the drained swamps. Another 1.4 billion tons go up in smoke from fires lit to clear rain forest for plantations, smoke that often shrouds Singapore and Malaysia in an impenetrable haze for weeks at a time.

Together, those 2 billion tons of CO2 account for 8 percent of the world's fossil fuel emissions, the report said. Draining the peat swamps to grow palm trees has had a very negative impact. Not only has it increased carbon emissions significantly, but it has also destroyed wetland ecosystem that can take carbon out of the atmosphere.

Update 2010: Global Warming Debate Continues

Since this article was written nearly 10 years ago, the debate over the impact of manmade CO2 from burning fossil fuels on Global Warming has not been resolved. Most governments are still proceeding on the assumption that Global Warming is real, and that it is the result of manmade CO2.

Some people are now challenging that assumption based on studies that show CO2 from natural sources (the ocean, the decomposition of organic matter, natural forest fires, volcanoes, etc.) produce 97 percent of the CO2 in the atmosphere. What's more, atmospheric water vapor has a far greater impact on heat retention and cooling than CO2, so we may be focusing on the wrong gas! Methane released from permafrost is also a growing concern if global warming continues. Others site recent changes in solar activity as a major factor in global warming.

Regardless of the conflicting results, the Obama administration has asked the EPA to increase the Corporate Average Fuel Economy (CAFE) requirements for auto makers significantly over the next six years. Auto makers will be required to raise their CAFE numbers to 35.5 mpg by 2016, which will reduce greenhouse gas (GHG) emissions of the average vehicle to 250 grams per mile. Achieving this goal will require roughly a 5 percent increase in fuel efficiency each year, starting in model year 2012. The gains will be achieved by switching to smaller displacement, more efficient engines. Many of these will have direct fuel injection, be turbocharged, and have additional add-on fuel saving features such as cylinder deactivation under light load, and/or start-stop systems to turn the engine off when the vehicle is not moving.

Critics say the new CAFE rules are too little too late. And what good will it do to improve our CAFE numbers if China keeps pumping millions of tons of CO2 into the atmosphere from all their coal-fired power plants? Add to that China's exploding car population, which may catch up and surpass that in the U.S. and Europe withing the next decade, and it adds up to a LOT of new CO2 that can't be offset by better fuel economy rules.

We'll keep you posted....

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