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Apparently driving a car is the single most polluting thing that most people do. Is it really true? We explore the implications of driving.

17 Dec 2007 | Category: Miscellaneous Advice

I have a friend, P, who is a bit of a diet freak. When we first met, I was amazed by how she carefully counted all the calories she was ingesting with every meal, snack and bite she took, and would never allow herself to exceed a certain limit. When the Atkins diet started to become popular, she switched from counting calories to counting carbs instead. And this year, she is counting something new yet again - and it has nothing to do with food. These days, P counts carbon.

"Counting carbon" first gained popularity when more and more people are started to take notice of how the excessive emission of carbon dioxide and other greenhouse gases has been contributing greatly to global warming and other resultant environmental problems, and decided to start examining and then making modifications to their own living habits and lifestyle choices in a bid to reduce their individual impact. It involves recording and restricting the amount of carbon dioxide one emits, the way calorie-counters record and restrict the number of calories they ingest (or the way carb-counters record and restrict the volume of carbohydrates they ingest). More often than not, it causes one to discover just how much one's actions actually contribute to the phenomenon of global warming.

At the top of this list is the act of driving; according to the U.S. Environmental Protection Agency, driving a car is the single most polluting thing that most people do.

This is because driving involves the combustion of petrol, a reaction whose primary by-product is carbon dioxide. As we all know, the Earth receives energy from the Sun in the form of radiation. Some of this energy is reflected back into space, but carbon dioxide and other greenhouses gases in the atmosphere trap the sun's energy, causing the Earth to heat up. For the Earth's temperature to be in steady state, the absorbed solar radiation must be balanced with the energy reflected back into space. However, a human-driven increase in carbon dioxide is causing more and more of the sun's energy to be trapped in the Earth's atmosphere instead of being reflected back into space, causing the Earth's temperature to rise excessively and resulting in global warming.

Cars account for about 10% of anthropogenic, or human-caused, greenhouse gas emissions globally; in industrialized cities, this figure rises to more than 50%. Experts on greenhouse gas emissions have calculated that every time a car burns 1 litre of petrol, it releases around 3 kilograms of carbon dioxide into the atmosphere, as well as a smaller amount of methane, nitrous oxide, and various other toxic gases. This figure is shocking in more ways than one. One litre of petrol weighs less than 1 kilogram. So how in the world could it release such a huge amount of poisonous gases - almost 3 times its original weight? Is this all just some mumbo jumbo conjured up by alarmist environmentalists to hoodwink us into joining their camp?

However, upon more detailed analysis, it all starts to make sense. In actual fact, this seemingly extraordinary phenomenon is the result of a very ordinary chemical equation that many of us learnt when we were in secondary school - C + O2 -> CO2. Petrol is almost entirely made up of carbon. When driving, petrol combusts, and every atom of carbon in the petrol combines with two atoms of oxygen to produce carbon dioxide. So factor in the original kilogram of carbon, combined with more than 2 kilograms of oxygen, and there you have it - each time you use up a litre of petrol, 3 kilograms of CO2 are launched into the atmosphere, helping to trap solar heat and causing the Earth's temperature to rise drastically.

How then can we help to reduce these emissions?

Because of their increased fuel efficiency relative to petrol-powered vehicles, diesel-powered cars are sometimes seen as an improvement. However, diesel emits more soot than petrol, and black carbon, contained in soot from the combustion of fuels, may be responsible for around 16% of the gross warming the planet is currently experiencing. According to testimony provided by five scientists before the US House Committee on Oversight and Government Reform, black carbon may be the second-most significant global warming pollutant after carbon dioxide. Once soot warming is factored in, it is obvious that switching to diesel is no solution at all.

Instead, according to Dr. Mark Z. Jacobson, Prof. of Civil and Environmental Engineering, Atmosphere/Energy Program, Stanford University, "[a] more certain method of reducing global warming caused by both fossil-fuel soot and carbon dioxide is to convert vehicles from fossil fuels to electric, plug-in hybrid or hydrogen fuel cell vehicles, where the electricity or hydrogen is produced by a renewable energy sources, such as wind, solar geothermal, hydroelectric, wave, or tidal power." The 2.5-litre Volvo V70 Cross Country, for example, annually produces 13 tons of greenhouse gas emissions. A more lightweight hybrid like the Ford Escape would cut greenhouse gas emissions over the same time period to 9 tons. But with a lighter hybrid, like a Toyota Prius sedan, this could be further reduced to 5 tons.

Recent news reports have shown that hybrid cars now account for some of the most popular car models in Hollywood. The Toyota Prius tops this list, counting such A-listers like Cameron Diaz, Leonardo DiCaprio, Carole King, Billy Joel and David Duchovny in its list of famous owners. This seems to have sparked off a trend where more and more consumers now opt for hybrid cars with much lower contributions to global warming than traditional petrol-powered cars. And we approve.

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