Putting a wedge in global warming

By Jill Hahn

The argument over global warming has shifted, from whether it’s real to what we ought to do about it.
On the one hand are those who’ll give you advice about what you, the individual consumer, can do to help. Buy energy-efficient appliances. Trade in your SUV for a hybrid. Change your lightbulbs to compact fluorescents.

On the other hand are those who point out that global warming is a problem of - well, of global dimensions, and your noble yet pitiful attempt to help is like hoping the ocean will care if you remove a drop of water. What you really need to do is learn how to adapt. Get flood insurance. Make sure your air-conditioning works.

So should you change your behavior, or is it pointless? In order to answer that, we need to get a handle on the magnitude of the problem, and the magnitude of your potential response.

Before the industrial age, Earth’s atmosphere contained about 280 parts per million (ppm) of CO2. Today the concentration of CO2 stands at about 375 ppm. There is some agreement that, in order to prevent most of the damaging climate change predicted by global models, we need to limit future atmospheric CO2 concentrations to no more than 500 ppm.
Robert Socolow and Stephen Pacala, economists at Princeton University, asked what we would need to do in order to keep atmospheric CO2 from climbing past 500 ppm in the next 50 years. They found that carbon emissions would need to be held near the present level of 7 billion tons (or gigatons) of carbon per year (7 GtC/year) for the next 50 years. There’s a problem, though: emissions are currently on course to more than double in that time, pushing atmospheric CO2 concentrations past 700 ppm.

So Pacala and Socolow made a graph. The top line rises as emissions will if we continue “business as usual.” The bottom line is horizontal, holding steady at 7 billion tons of carbon per year. Pacala and Socolow then divided the difference between the top line and the bottom line into seven equal ‘wedges.’ Each wedge represents an emission-reducing activity that starts at zero today and increases until it accounts for a cumulative total of 25 GtC of reduced emissions over 50 years. In other words, if we can find seven different ways of lowering emissions by 25GtC over the next fifty years, we’ll keep ourselves below the ceiling of 500 ppm of atmospheric CO2.

Gigatons – that’s a lot of carbon. Trading in one SUV won’t do the trick. But what if we insisted that every new car sold in the United States be twice as fuel-efficient as the current fleet? That wouldn’t be hard to achieve, considering that right now the average American passenger car gets 22.4 mpg, while vans, pickups, and SUVs average a measly 16.2 mpg. Pull out your scratch paper.

We buy lots of new cars and light trucks in the US, 6.6 million in 2003 alone. If we doubled the fuel efficiency of these new vehicles, we would save over 5 billion gallons of gasoline per year. Each gallon of gasoline accounts for about 3 kg of carbon, so our new vehicles would save 17 million tons of C in a year. Over 50 years, the savings from that one year’s worth of new, more fuel-efficient automobiles would accrue to 846,387,000 tons, or 0.8 GtC.
Assuming that the same number of new vehicles is built each year for 50 years, these more efficient vehicles would save 21 GtC, almost an entire wedge. Buying that hybrid may represent only a tiny drop, but mandating higher fuel efficiency for all new vehicles would go a long way towards stopping draining the ocean.

What about potential energy savings in your home? Dr. William Moomaw, Director of the Center for International Environment and Resource Policy at Tufts University, recently built a new home that uses one-third the energy of a conventional house. That’s a high bar to achieve, but “my contractor,” says Dr. Moomaw, “… has built houses that … use 2/3 of the energy of a standard house at no extra cost.”

We know how many new houses are built in the U.S. in a given year, and how much energy they use annually, because the U.S. Census and the Department of Energy keep track of it. We can therefore calculate annual carbon emissions due to new homes (not counting AC): 3,363,228 metric tons.

Let’s be conservative and imagine that these houses were built to be 25% more energy-efficient. That would save us 840,807 metric tons of carbon each year. Over 50 years, adding a million energy-efficient new houses each year, we get a total savings of 1GtC, or a twenty-fifth of a wedge. So, although buying an energy-efficient refrigerator is a responsible thing you can do right now, it’s changing how we build all new buildings that will really make a difference to the planet. And the sooner we begin, the more of an impact we’ll have, since accrued over fifty years, it’s the early changes that make the most difference.

And what about lightbulbs? In 2001, lighting accounted for 101 billion kilowatt hours of U.S. household electricity use, which translates about 105 metric tons C. Compact fluorescents would save 66% of that, or about 5 GtC over 50 years. That’s a fifth of a wedge, if we simply replaced every lightbulb in every home in America with compact fluorescents. How many people does it take to change a lightbulb? Everybody, if we want to change the world.

Jill Hahn, a Newton Highlands resident, is a biologist, a writer, and a mom. All three roles contribute to her interest in environmental issues. She can be reached at jkkhahn@comcast.net.

This article is archived at www.greendecade.org/environmentpage.html