Heat we emit could warm the Earth

• New Scientist
• 26 November 2008 by Mark Buchanan
• http://www.newscientist.com/article/mg20026845.200-heat-we-emit-could-warm-the-earth.html?DCMP=NLC-nletter&nsref=mg20026845.200
• Magazine issue 2684. Subscribe and get 4 free issues.
• For similar stories, visit the Energy and Fuels and Climate Change Topic Guides

EVEN if we turn to clean energy to reduce carbon emissions, the planet might carry on warming anyway due to the heat released into the environment by our ever-increasing consumption of energy.

That's the contentious possibility raised by Nick Cowern and Chihak Ahn of the School of Electrical, Electronic and Computer Engineering at Newcastle University, UK. They argue that human energy consumption could begin to contribute significantly to global warming a century from now.

Cowern and Ahn considered an emissions scenario proposed by James Hansen of the Goddard Institute for Space Studies in New York, and others. Under this scenario, which envisages greenhouse gases being cut significantly through phasing out coal over the next 40 years, Cowern and Ahn calculate that the greenhouse effect will start to diminish by 2050, stabilising the climate.

But things may not go according to plan. The energy we generate and consume ultimately ends up being dissipated into the environment as heat. This input is relatively small today but might become significant in the next century, Cowern and Ahn suggest.

Their calculations show that if global energy use increases at about 1 per cent per year - slower than in the recent past - then by 2100, the heat dissipated could become significant enough to cancel out the benefits of cuts in emissions (www.arxiv.org/abs/0811.0476).

Being aware of this potential problem should inform what types of clean energy we adopt, say the pair. Nuclear power has the most harmful effect in that it releases energy that is otherwise locked up. Solar power is better as it exploits energy that the Earth is absorbing anyway, though Cowern and Ahn point out that solar cells tend to absorb more energy from the sun's rays than Earth's surface does, some of which ends up warming the local environment. One way round this could be to develop solar cells which absorb only the most energetic frequencies in the sun's rays. This could be done using "wide band gap" photovoltaic cells, containing layers that reflect low-frequency rays back. In the meantime, the cleanest energy options are wind and tidal power, say the researchers, as these tap into energy flows already present on Earth without significantly affecting them.

Cowern and Ahn's argument is logical, says Jonathan Gregory, a climate expert at the University of Reading, UK. "Human energy dissipation is currently small compared with other factors, but you can imagine it becoming much bigger." However, he adds that energy production would need to grow significantly for the effect to kick in. "It's fair to ask if we could ever produce so much power," he says.