April 2010


Global Warming &Vehicles24 Apr 2010 03:54 pm

Our morning got off to a curious start, to my mind. When my 17-year-old finally awoke, my wife asked if she wanted to come along for a jog.

“No,” she replied, “I have an extra maths lesson in one hour.”

“That’s fine,” I said, to my wife. “You run, and I will walk her to maths.” (1.8 km away)

“Walk?,” exclaimed my wife, “She doesn’t have time for that; she has tons of homework.”

If the humour of this conversation does not immediately occur to you, perhaps you should exercise your mind. Our culture has compartmentalized each aspect of our lives so completely that exercise is a specialized activity done purely for its own sake and worth the time it requires. Traveling to school, work, shops, friends or errands is a separate activity, to be done as quickly as possible, by car. Using a slower mode of transport is a waste of time, even if it involves exercise. But my calculations show that traveling more slowly actually saves me time, in two ways.

I jog for exercise and pleasure and cycle to get around and also for pleasure. It horrifies me to see people who will ride a bicycle all the way to the Magaliesburg on a Saturday morning for fun, get home, shower and hop in the car to get to the post office. I’ve seen this happen.

My longest regular ride is to a weekly voice lesson. It’s a 7.5 km trip by car that takes 15 minutes, or a cycle of anywhere from 25 to 35 minutes. On the morning of my voice lesson, I skip my usual one-hour jog, saving the same time that it will take me to cycle in both directions. Jogging and then driving would together take an hour and a half. Cycling takes one hour. 60 + (15 x 2) – (30 x 2) = 30. I save a half hour.

That’s not all I save. I don’t keep track, but I figure that sometime this year I will have made my hundredth cycle to my lesson. 100 x (7.5 x 2) = 1,500. That’s 1,500 kms of driving I have saved—farther than Johannesburg to Cape Town—and 150 litres of petrol worth well over a thousand rand. The environment has been spared more than 350 kg of carbon dioxide.

Let’s exercise our maths some more. A health study following more than 5,000 people over 40 years concluded that exercise equivalent to walking for 30 minutes a day for five days a week adds 1.3 to 1.5 years to your life.  Do those regular walks for 30 years, and you will spend 234,000 minutes walking, (30 x 5 x 52 x 30 = 234,000) but will have added 735,840 minutes to your life. (1.4 x 60 x 24 x 365 = 735,840.) So the averages tell me that the 20 minute stroll to her maths lesson added perhaps an hour to my daughter’s life. 735,840 ÷ 234,000 x 20 = 62.89. And, she later reported, “It was a pleasant walk.”

1 + 1 = 2.

Garden &Global Warming23 Apr 2010 03:24 pm

After two weeks of municipal strikes, the wheelie bins lining the roads are starting to bulge . . . and smell. There’s one plus to this, however. Since the surplus of refuse is literally lifting the lids of the bins, I’ve been able to get an easy look at what people are throwing away. To a large extent, they are throwing away greens. And there’s nothing green about that.

One of the most dangerous myths about the environment is that it is better to send something biodegradable to a landfill than something that will last a hundred years, like a plastic bottle. Quite frankly, that’s a load of garbage.

The last thing you want to happen in a landfill is biodegradation. Deep in a landfill, in the absence of oxygen, bacteria break down plant material into methane. This gas is 21 times more potent as a greenhouse gas than carbon dioxide. If garden waste is composted or left to decompose in the garden, it will give off some carbon dioxide, but not more than it absorbed when it was growing. So sending plants to the landfill is at least 21 times worse for the atmosphere than composting them.

Grass clippings are the worst, since they decompose much faster than, say, twigs. It is impossible to precisely calculate these things, because of the many variables in landfills, but a reasonable estimate based on a thorough scientific report, is that 1 kg of garden waste in a landfill will give off 77 grams of methane. This means that a full, standard black refuse bag (750mm x 950mm) containing  14 kg of grass clippings will give off as much greenhouse gasses as burning 9.5 litres of petrol by driving nearly 100 kilometres. Recycling the equivalent quantity of plastic—the same bag filled with 3 kgs of empty PET plastic bottles—would save less than a sixth as much greenhouse gases as composting that bag full of grass.

Our lawn space is considerably smaller than many suburban gardens. But my gardener says that in the summer, he mows about two bags worth of clippings twice a week. So in some months, our grass clippings would be causing as much damage to the atmosphere as the electricity consumed by our house, if we were throwing these clippings out with the garbage.

But we don’t. I don’t have much energy for composting, so just a fraction of the clippings go into a somewhat neglected compost pile, which nonetheless manages to produce some good compost in time. The rest is stored in reusable large woven polypropylene bags until we have a carload. Then I haul them a couple of kilometres to the nearest Pikitup garden refuse transfer site, so the municipality can compost for me. It’s a small inconvenience to keep my grass truly green.