Energy waste causing another global warming

Bina Venkataraman

Human civilisation will heat up the planet; the glaciers will melt and the seas will rise. It's a familiar refrain by now, with a familiar solution: stop pumping out the greenhouse gases that trap the sun's heat.

But even if we bring the greenhouse effect under control, says a Tufts astrophysicist, the earth will warm up anyway, thanks to a completely different source of heat that we create ourselves.

Over the next 250 years, calculates Eric J. Chaisson in a recent paper, the earth's population will start generating so much of its own heat - chiefly wasted from energy use - that it will warm the earth even without a rise in greenhouse gases. The only way to avoid it, he says, is to rethink how we generate energy.

His paper examines the planet's growing pool of waste heat, a widespread phenomenon that nonetheless has been little studied as a cause of climate change.

Nearly everything that uses or generates energy - chiefly power plants, but also cars, snowblowers, computers, and light bulbs - squanders some energy as wasted heat. And the larger and more energy-hungry the human population grows, the more waste heat remains in our atmosphere.

"What this means for humans is that this is the ultimate limit to growth," said Dennis Bushnell, the chief scientist at NASA's Langley Research Center, who urged Chaisson to publish his idea. "As we produce more kilowatts, we have to produce more waste heat."

Heat loss

Chaisson's prediction suggests we need to change our energy policy - not just by keeping emissions low, but by shifting toward power sources that don't add new heat to the earth's system.

The culprits in the waste-heat problem are not only dirty fossil fuels like coal and oil, but also some "clean" power sources like nuclear and geothermal energy, which still add to the problem by pumping new heat into the atmosphere.

The only way to stop waste heat-induced global warming, in Chaisson's view, is to rely on energy that already reaches the earth's surface: sunlight, and the wind and the waves that it powers.

Critics say Chaisson's paper describes a scenario so far in the future, and so dependent on projections, that there's simply no way to know if it will come to pass. They also say it could distract us from the far more urgent problem of greenhouse gases.

But the idea has piqued the interest of several scientists from around the world who see an opportunity to avert a crisis before future generations have to face it.
The more energy humans use to fuel our societies and to feed our populations, the more waste heat we will emit

Chaisson published his paper last year in a journal of the American Geophysical Union. Since then, he has received a flurry of e-mails from intrigued researchers and has spoken about it at conferences from the West Coast to Europe.

His predictions are based on a simple but fundamental law of science: Energy can't be perfectly harnessed, but tends to dissipate, usually in the form of heat. The concept, also known as entropy, is laid out in the inviolable second law of thermodynamics.

In practice, this means that any machine we run, whether a car engine or a power plant, not only does the work we're asking it to do, but emits heat - a lot of heat. Think of touching a lightbulb, or holding your hand over your exhaust pipe after your car has been running for only a few minutes. The heat you feel is energy radiating uselessly into the air.

Preparing for future

Altogether, humans waste about two-thirds of the energy we produce on earth. Currently, all this heat makes little difference for our climate: it mostly dissipates into space. But the more energy humans use to fuel our societies and to feed our populations, the more waste heat we will emit.

Eventually, as more economies industrialise, and as the population grows, that heat will become a significant problem.

Today, many climate scientists view waste heat as a negligible problem compared to greenhouse gas emissions. The heat-trapping effect of greenhouse gases has 100 times the effect on global warming that waste heat does, said Mark Flanner, a researcher at the National Center for Atmospheric Research in Boulder, Colorado, who uses computer models to simulate waste heat. Flanner agrees with Chaisson, however, that it will play a much larger role over the long term.

"If we assume the current growth in non-renewable energy use, the heat flux will be of equal magnitude to the greenhouse effect 200 years from now," he said.

Still there are several big unknowns in Chaisson's predictions. One is his assumption that power plants and engines will continue to be quite wasteful. History suggests that societies tend to become more, not less, energy-efficient as technologies improve.

Today's machines are far more efficient than yesterday's, and if that trend continues, the problem of global waste heat could be slower to develop - although the laws of thermodynamics say it's impossible to reduce wasted energy to zero.

Also uncertain is how much waste heat the planet's oceans can absorb before the overall temperature rises. And Chaisson's starkest scenarios assume that the human population will grow at certain rates, although it could drop sharply from widespread disaster or disease.

Chaisson warns that taking a long-term view is vital to human survival - even if the coming environmental catastrophe is something that neither we, nor our children, are likely to see in our lifetimes.

Source : The Boston Globe