I'm pretty sure that in Fred Pohl's early 1980s energy and climate change novel "The Cool War" the fundamental heating issue is waste heat, rather than greenhousing
On Jan 28, 7:42 am, Andrew Lockley <andrew.lock...@gmail.com> wrote: > A few months back we discussed a controversial set of papers which > considered the effect of 'renewable' energy on the climate system. > > NewScientist is a popular and respected UK magazine, and has covered the > issue in detail, including discussions with group members. > > http://www.newscientist.com/article/mg21328491.700-power-paradox-clea... > reqd, pasted) > > A > > Power paradox: Clean might not be green forever > > 25 January 2012 by Anil Ananthaswamy and Michael Le Page Magazine issue > 2849. Subscribe and save > > As energy demand grows, even alternative energy sources such as wind, solar > and nuclear fusion could begin to affect the climate > > "A better, richer and happier life for all our citizens." That's the > American dream. In practice, it means living in a spacious, air-conditioned > house, owning a car or three and maybe a boat or a holiday home, not to > mention flying off to exotic destinations. > > The trouble with this lifestyle is that it consumes a lot of power. If > everyone in the world started living like wealthy Americans, we'd need to > generate more than 10 times as much energy each year. And if, in a century > or three, we all expect to be looked after by an army of robots and zoom up > into space on holidays, we are going to need a vast amount more. Where are > we going to get so much power from? > > It is clear that continuing to rely on fossil fuels will have catastrophic > results, because of the dramatic warming effect of carbon dioxide. But > alternative power sources will affect the climate too. For now, the > climatic effects of "clean energy" sources are trivial compared with those > that spew out greenhouse gases, but if we keep on using ever more power > over the coming centuries, they will become ever more significant. > > While this kind of work is still at an early stage, some startling > conclusions are already beginning to emerge. Nuclear power - including > fusion - is not the long-term answer to our energy problems. Even renewable > energies such as wind power will have to be used with caution, because > large-scale extraction could have both local and global effects. These > effects are not necessarily a bad thing, though. We might be able to > exploit them to geoengineer the climate and combat global warming. > > There is a fundamental problem facing any planet-bound civilisation, as > Eric Chaisson of the Harvard Smithsonian Center for Astrophysics in > Cambridge, Massachusetts, points out. Whatever you use energy for, it > almost all ends up as waste heat. > > Much of the electrical energy that powers your mobile phone or computer > ends up heating the circuitry, for instance. The rest gets turned into > radio waves or light, which turn into heat when they are absorbed by other > surfaces. The same is true when you use a mixer in the kitchen, or a drill, > or turn on a fan - unless you're trying to beam radio signals to aliens, > pretty much all of the energy you use will end up heating the Earth. > > We humans use a little over 16 terawatts (TW) of power at any one moment, > which is nothing compared with the 120,000 TW of solar power absorbed by > the Earth at the same time. What matters, though, is the balance between > how much heat arrives and how much leaves (see "Earth's energy budget"). If > as much heat leaves the top of the atmosphere as enters, a planet's > temperature remains the same. If more heat arrives, or less is lost, the > planet will warm. As it does so, it will begin to emit more and more heat > until equilibrium is re-established at a higher temperature. > > Over the past few thousand years, Earth was roughly in equilibrium and the > climate changed little. Now levels of greenhouse gases are rising, and > roughly 380 TW less heat is escaping. Result: the planet is warming. > > The warming due to the 16 TW or so of waste heat produced by humans is tiny > in comparison. However, if humanity manages to thrive despite the immense > challenges we face, and keeps on using more and more power, waste heat will > become a huge problem in the future. If the demand for power grew to 5000 > TW, Chaisson has calculated, it would warm the planet by 3 °C. > > This waste-heat warming would be in addition to the warming due to rising > CO 2 levels. What's more, since this calculation does not take into account > any of the feedbacks likely to amplify the effect, well under 5000 TW may > produce this degree of warming. > > Such colossal power use might seem implausible. Yet if our consumption > continues to grow exponentially - it has been increasing by around 2 per > cent per year this century despite rising prices - we could reach this > point around 2300. > > Chaisson describes his work as a "back of the envelope" calculation done in > the hope someone would prove him wrong. So far no one has. On the contrary, > preliminary modelling by Mark Flanner of the National Center for > Atmospheric Research in Boulder, Colorado, suggests that waste heat would > cause large industrialised regions to warm by between 0.4 °C and 0.9 °C by > 2100, in agreement with Chaisson's estimates (Geophysical Research Letters, > vol 36, p L02801). Normal climate models do not include the waste-heat > effect. > > Does this mean human civilisation has to restrict itself to using no more > than a few hundred terawatts of energy? Not necessarily. It depends on > where the energy comes from. If you turn the sun's energy into electricity > and use it to boil your kettle, it won't make the planet any warmer than if > that same energy had instead gone into heating up the tiles on your roof. > But if you boil your kettle using energy from fossil fuels or a nuclear > power plant, you are adding extra heat. "The only energy that is not going > to additionally heat the Earth is solar and its derivatives," says > Chaisson, referring to sources driven by the sun's heat - wind, hydro and > waves. > > So although nuclear fusion could in theory provide an effectively unlimited > source of energy, if our energy demand keeps growing we will not be able to > use it freely without significantly warming the planet. > > It seems Chaisson's mentor, Carl Sagan, was right. "Sagan used to preach to > me, and I now preach to my students," says Chaisson, "that any intelligent > civilisation on any planet will eventually have to use the energy of its > parent star, exclusively." More specifically, they will be limited to the > solar energy that is normally absorbed by their planet - anything extra, > including space-based solar, is out. > > Waste-heat warming > > In theory an advanced alien civilisation could produce a lot of waste heat > and still maintain a stable climate by using geoengineering to counteract > waste-heat warming. On Earth, though, there is probably little scope for > reducing greenhouse gas levels much below preindustrial levels, because > plants need CO 2 . Shading the planet or increasing its reflectivity would > be problematic, too. > > Chaisson accepts that warming from waste heat is not important now. > Nevertheless, he argues that we might as well switch to solar-based > energies as soon as possible. "Everyone agrees that something must be done > to stop the rise of CO 2 in the near term, and then we need to worry about > excess heating of our atmosphere by energy usage in the long term," he > says. "My point is that if we can do both at the same time, then why not > take the steps now to do just that?" > > That's music to the ears of Mark Jacobson of Stanford University in > California. He has been pushing an ambitious plan for a wholesale switch to > renewable energy by 2030. He envisages wind and solar providing 90 per cent > of this (Energy Policy, vol 39, p 1154). Yet on these kinds of scales, even > renewable power sources could begin to affect the climate. > > Take wind power. In 2010, Somnath Baidya Roy at the University of Illinois > in Urbana-Champaign reported that wind farms affect their local climate. > Long-term data from a wind farm at San Gorgonio, California, confirmed his > earlier model predictions: surface temperatures behind the wind turbines > were higher than in front during the night, but as much as 4 °C lower by > day. > > Roy thinks the turbulence created by the turbines sucks air down from > above. During the day, when the hottest air is usually near the surface, > this has a cooling effect. At night, when the air near the ground may be > colder than that above, it can have a warming effect. > > These effects could be minimised by placing wind farms in areas where > there's already a lot of turbulence. But we might not want to minimise > them. "Some of these effects are actually welcome for agricultural > reasons," says Cristina Archer at the University of Delaware in Newark, who > studies wind power. Strategically placed wind farms might keep crops cool > in summer and reduce the risk of frost in other seasons. Farmers in > California and Florida already use wind machines to fight frost by pulling > down warmer air. > > Do offshore wind farms affect sea surface temperatures and evaporation > rates? Could these local effects add up to produce significant regional or > even global effects? Perhaps. Winds obviously play a major role in climate. > Slowing or altering wind patterns will alter the movement of heat and water > around the planet, and thus temperature and rainfall. > > It might seem inconceivable that humans could have a significant effect on > the wind, but we may already be doing so. While wind speeds over the oceans > are increasing, surface winds over Europe, Asia and North America have > slowed by up to 15 per cent on average since 1979. At least half of the > slowdown is thought to be due to changes in land use, with more vegetation > and possibly more buildings making the terrain rougher (Nature Geoscience, > vol 3, p 756). > > A 2004 study by David Keith of the University of Calgary in Alberta, > Canada, suggested that the climatic effects of wind power might start to > become apparent at a level of 2 TW. According to Axel Kleidon and Lee > Miller of the Max Planck Institute for Biogeochemistry in Jena, Germany, > the impact of wind power depends on what proportion of the available power > we extract. They recently calculated how much wind energy there is from the > top down, starting with the incoming solar radiation that drives the winds > by creating temperature differences in the atmosphere. They concluded that > at most 68 TW could be extracted. Further modelling suggested there could > be as little as 18 TW available - far lower than other estimates. > > Even more controversially, the team claimed that extracting all the > available wind power would produce big changes in temperature and > precipitation. While they are not suggesting the world will warm overall, > according to their model the local changes are comparable in magnitude to > those associated with a doubling of CO 2 . > > Even if this conclusion is correct, we are nowhere near to extracting this > level of wind power. At the end of 2011, worldwide wind power generation > capacity was just 0.2 TW. And many others in the field are extremely > sceptical about the team's conclusions. "I don't believe their results," > says Archer. > > "The idea that [the impact] is on par with doubling of CO 2 , that's just > nonsense," agrees climate scientist Gavin Schmidt of the NASA Goddard > Institute for Space Studies in New York. There will be some impact of > large-scale wind-power generation, but Miller's team is overstating it, he > says. > > According to Archer and Jacobson's bottom-up estimates, which unlike > Kleidon's are based on actual measurements of wind speeds, there is 1700 TW > of wind power at an altitude of 100 metres over land and sea. Of this, > between 72 and 170 TW could be extracted in a practical and > cost-competitive manner. > > Modelling by Jacobson's team suggests that extracting 11.5 TW of this wind > power would reduce the kinetic energy of wind at 100 metres by less than 1 > per cent. The effects on temperature and precipitation are so small they > cannot be distinguished from natural variability, he says. > > Solar cooling > > The science is far from settled. Yet even if wind farms do turn out to have > significant climatic effects, we might be able to turn this to our > advantage. Perhaps carefully placed wind farms could boost rainfall in arid > regions, for instance. It might even be possible to use wind power as a > form of geoengineering (see "Generate energy, cool the planet"). "Could > some of the climatic impacts of near-surface wind power be desirable? > Absolutely," says Miller. But this type of research is only beginning, he > points out. What is clear, of course, is that every wind farm that goes up > means less CO 2 pumped into atmosphere. > > Compared with solar power, though, wind resources are relatively small. "I > think that there is simply not enough wind energy capturable on Earth to do > much good in the long term," says Chaisson. "Nor with water and waves. The > only way to endure is to learn how to utilise the sun's energy." Thousands > of terawatts of solar power could be generated just using existing > technology. > > Even solar power can affect climate, though, because solar panels can alter > the reflectivity, or albedo, of the surface. One recent study modelled the > effects of building a 1-TW solar power plant in the Mojave desert in > California. It concluded that placing so many dark solar panels over > light-coloured sand will warm the air above by 0.4 °C, affecting > temperature and wind patterns within a 300-kilometre radius. > > If we develop much more efficient solar panels in the future, though, a > similar solar plant would cool the local area. The heat would end up > wherever the energy is eventually used. Indeed, even existing solar panels > can have a local cooling effect if they are placed over dark surfaces, such > as black roofs. "Solar panels will basically take 20 per cent of sunlight > and convert it to electricity," says Jacobson. "That cools down your house." > > What's more, many other human activities, from building cities to planting > crops, alter albedo, and these activities have a much greater impact > because they affect a far greater proportion of Earth's surface. Air > temperatures in south-eastern Spain have fallen more than 0.6 °C since 1983 > because there are so many reflective greenhouses in the area, for instance. > > So while the large-scale use of solar power could potentially affect the > climate, the effects will be relatively minor so long as we don't capture > hundreds of terawatts that would otherwise have been reflected straight > back into space. Careful design and placement of solar plants should > minimise any negative consequences. > > Some regard any discussion of the climatic effects of renewable energy, and > waste heat, as a distraction from the far more urgent task of cutting > greenhouse gas emissions. But if we do not start thinking about it now, we > may one day discover that in trying to solve one climate problem, we have > created another. > > Generate energy, cool the planet When we talk of extracting wind energy, > it's mainly from wind at an altitude of about 100 metres. But wind speeds > increase the higher you go. In the four jet streams that circle Earth more > than 10 kilometres up, wind speeds of well over 100 kilometres per hour are > typical. > > Exploiting this energy will not be easy, not least because of the way the > jet streams meander and change location, but several groups are developing > ways to do it. Most involve tethered turbines or kites that turn generators > on the ground. > > According to some estimates, the available energy in the jet streams is > about 100 times the current global energy demand. Simulations by Cristina > Archer at the University of Delaware in Newark and Ken Caldeira of Stanford > University in California suggest that extracting enough energy from > high-level winds to meet all our current energy demands would have no > significant impact on global climate. But their model suggests that > extracting larger amounts would have a big impact. In the extreme case of > extracting 1000 TW, mean surface temperatures fell nearly 10 °C, total > rainfall decreased by about 35 per cent and sea ice cover doubled > (Energies, vol 2, p 307). > > The reason, says Caldeira, is that slowing down the high-altitude winds > would slow the heat transfer between the equator and the poles. This would > cause the equator to warm and the poles to cool, increasing sea ice cover. > More sea ice means more heat is reflected from the poles. The end result is > that the equator warms slightly, but the poles cool significantly. > > This effect might actually be desirable to counteract global warming, given > that the Arctic is warming faster than any other area on Earth and losing > sea ice fast. So could we deliberately induce it? "This is one of the > things we plan to look at in the future," says Caldeira. > > However, Axel Kleidon and Lee Miller of the Max Planck Institute for > Biogeochemistry in Jena, Germany, claim Archer and Caldeira have massively > overestimated the amount of energy that could be extracted. They think the > high wind speeds in the jet streams are a result of a near lack of > friction, rather than a constant input of energy. As a result, they > estimate that only about 7.5 TW of power could be extracted from the jet > stream, and that even this would have a major effect on climate (Earth > System Dynamics, vol 2, p 201). > > From an energy perspective this would be bad news, but it makes cooling the > planet this way seem more feasible. According to their model, though, the > planet would cool just 0.5 °C, with the Arctic getting 2 °C cooler but the > Antarctic warming by 2 °C, among other effects. We will obviously need to > have a far better understanding of the changes before we even begin to > entertain the notion of geoengineering, Miller says. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
