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Swallow your pride
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THE LAST WORD Put that light out If the sun was extinguished or there was a permanent worldwide eclipse, how long would it take for us all to freeze to death, and is there anything we could do to stay alive?
■ A back-of-the-envelope calculation suggests the whole Earth might freeze solid within 45 days, radiating away its thermal energy according to the Stefan-Boltzmann law, which relates energy loss of a body to its temperature. My calculations assume the vast bulk of the Earth’s captured solar energy is stored in the oceans, which have an average temperature of 15 °C down to a depth of 35 metres. Energy carried by water at greater depths doesn’t count because it would rapidly become isolated from the surface by ice floes. With its smaller heat capacity, the land would freeze much more quickly than the oceans. Air over relatively warm oceans would rise, pulling in cold air from the continents. This would chill the surface waters and might increase the circulation of water, exposing it to the chilling, perpetual night. Interestingly, the volcanic dust thrown up by the eruption of the Tambora volcano in 1815 acted both for and against cooling. The dust blocked out the sun, but it also reduced the escape of thermal radiation from the Earth by dint of a greenhouse effect. Sunlight dimmed by 25 per cent for a while, leading to a dip in global temperatures of 0.7 °C in
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
most parts of the Earth’s surface 1816. But the fall in temperature would be frozen within a few days. was small despite a big reduction The only exception would be near in sunlight, suggesting that the the coastline, where it might take a Earth might take longer to freeze few weeks because of the amount than 45 days. Indeed, freezing may well be delayed further by the of heat stored in the oceans. Could we stop this? Perhaps natural greenhouse effect that we could quickly burn the world’s comes with our atmosphere and the thermal inertia of our oceans. forests to release large amounts of carbon dioxide to help trap Nevertheless, Earth would still infrared thermal radiation. be able to support a colony of humans. There would still be “It’s likely that most plenty of energy in the form of parts of the Earth’s fossil and nuclear fuels, and surface would be frozen geothermal heat mines. But within a few days” without plants to replenish our oxygen supply, it would quickly run out, so we would need to build However, with only fossil fuels, biospheres with artificial light for nuclear and geothermal energy left to rely on, we’d still freeze plant photosynthesis. quickly. And if we didn’t, we’d Thankfully, switching off the soon run out of food and oxygen. sun is an experiment the Earth Simon Iveson will not undergo for another UPN Veteran University 5 billion years. Yogyakarta, Indonesia Mike Follows Willenhall, West Midlands, UK ■ The sun can’t be turned off like ■ You can estimate how long a light bulb. It glows because its it would take us to freeze by surface is about 5500 °C and is extrapolating from the rate of heated by the nuclear fusion cooling that happens overnight. inside its core which is even In areas with clear skies, the hotter – about 15,000,000 °C. temperature can drop to freezing Even if fusion in the core could in less than 12 hours. In places be switched off suddenly, the sun with heavy cloud cover, water would continue to radiate light vapour traps infrared radiation just as the heating element on an before slowing down the rate at electric stove gives off heat for a which it radiates away into space, time after you switch it off. so cooling takes much longer. Obviously, the sun is bigger and Here, the temperature drops by hotter than a stove, so would perhaps 5 °C in 12 hours. However, continue to radiate heat and light without the thermal energy of the for a long time. In addition, the sun constantly evaporating water, energy produced in the core of the this insulating cloud cover would sun takes time to work its way quickly disappear. It is likely that out – millions of years if you track
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
Do Polar Bears Get Lonely? A brand new collection ight serious enquiry, brilliant insight cted and the hilariously unexpected Available from booksellers m/ and at www.newscientist.com/ polarbears
the energy by following the paths of individual photons. The sun would cool a tiny bit each year, but as the sun cools it would contract, releasing gravitational energy that would heat it and offset some of the cooling. That’s how white dwarf stars continue shining. Suffice it to say that it would take many millions of years before our descendants even noticed. However, if the sun suddenly vanished, the Earth would cool quickly. Unprotected people would start freezing in days, but they could survive much longer if they went down into deep mines, warmed by the Earth’s heat. Jeff Hecht New Scientist contributing editor Auburndale, Massachusetts, US ■ Even if the sun went out, ecosystems around hydrothermal vents along the Earth’s mid-ocean ridges would continue to chemosynthesise using geothermal energy for a few thousand million years. So , business as usual for tube worms. Allan Mann Alnwick, Northumberland, UK
THIS WEEK’S QUESTION SWALLOW YOUR PRIDE
I’ve just seen a sword-swallowing act. Swords, seemingly longer than the depth from throat to anus were swallowed. It has to be a trick, doesn’t it? If it is, what’s the trick? If it isn’t, what’s going on? Alan Finnegan Whitehaven, Cumbria, UK
THE LAST WORD Put that light out If the sun was extinguished or there was a permanent worldwide eclipse, how long would it take for us all to freeze to death, and is there anything we could do to stay alive?
■ A back-of-the-envelope calculation suggests the whole Earth might freeze solid within 45 days, radiating away its thermal energy according to the Stefan-Boltzmann law, which relates energy loss of a body to its temperature. My calculations assume the vast bulk of the Earth’s captured solar energy is stored in the oceans, which have an average temperature of 15 °C down to a depth of 35 metres. Energy carried by water at greater depths doesn’t count because it would rapidly become isolated from the surface by ice floes. With its smaller heat capacity, the land would freeze much more quickly than the oceans. Air over relatively warm oceans would rise, pulling in cold air from the continents. This would chill the surface waters and might increase the circulation of water, exposing it to the chilling, perpetual night. Interestingly, the volcanic dust thrown up by the eruption of the Tambora volcano in 1815 acted both for and against cooling. The dust blocked out the sun, but it also reduced the escape of thermal radiation from the Earth by dint of a greenhouse effect. Sunlight dimmed by 25 per cent for a while, leading to a dip in global temperatures of 0.7 °C in
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
most parts of the Earth’s surface 1816. But the fall in temperature would be frozen within a few days. was small despite a big reduction The only exception would be near in sunlight, suggesting that the the coastline, where it might take a Earth might take longer to freeze few weeks because of the amount than 45 days. Indeed, freezing may well be delayed further by the of heat stored in the oceans. Could we stop this? Perhaps natural greenhouse effect that we could quickly burn the world’s comes with our atmosphere and the thermal inertia of our oceans. forests to release large amounts of carbon dioxide to help trap Nevertheless, Earth would still infrared thermal radiation. be able to support a colony of humans. There would still be “It’s likely that most plenty of energy in the form of parts of the Earth’s fossil and nuclear fuels, and surface would be frozen geothermal heat mines. But within a few days” without plants to replenish our oxygen supply, it would quickly run out, so we would need to build However, with only fossil fuels, biospheres with artificial light for nuclear and geothermal energy left to rely on, we’d still freeze plant photosynthesis. quickly. And if we didn’t, we’d Thankfully, switching off the soon run out of food and oxygen. sun is an experiment the Earth Simon Iveson will not undergo for another UPN Veteran University 5 billion years. Yogyakarta, Indonesia Mike Follows Willenhall, West Midlands, UK ■ The sun can’t be turned off like ■ You can estimate how long a light bulb. It glows because its it would take us to freeze by surface is about 5500 °C and is extrapolating from the rate of heated by the nuclear fusion cooling that happens overnight. inside its core which is even In areas with clear skies, the hotter – about 15,000,000 °C. temperature can drop to freezing Even if fusion in the core could in less than 12 hours. In places be switched off suddenly, the sun with heavy cloud cover, water would continue to radiate light vapour traps infrared radiation just as the heating element on an before slowing down the rate at electric stove gives off heat for a which it radiates away into space, time after you switch it off. so cooling takes much longer. Obviously, the sun is bigger and Here, the temperature drops by hotter than a stove, so would perhaps 5 °C in 12 hours. However, continue to radiate heat and light without the thermal energy of the for a long time. In addition, the sun constantly evaporating water, energy produced in the core of the this insulating cloud cover would sun takes time to work its way quickly disappear. It is likely that out – millions of years if you track
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
Do Polar Bears Get Lonely? A brand new collection ight serious enquiry, brilliant insight cted and the hilariously unexpected Available from booksellers m/ and at www.newscientist.com/ polarbears
the energy by following the paths of individual photons. The sun would cool a tiny bit each year, but as the sun cools it would contract, releasing gravitational energy that would heat it and offset some of the cooling. That’s how white dwarf stars continue shining. Suffice it to say that it would take many millions of years before our descendants even noticed. However, if the sun suddenly vanished, the Earth would cool quickly. Unprotected people would start freezing in days, but they could survive much longer if they went down into deep mines, warmed by the Earth’s heat. Jeff Hecht New Scientist contributing editor Auburndale, Massachusetts, US ■ Even if the sun went out, ecosystems around hydrothermal vents along the Earth’s mid-ocean ridges would continue to chemosynthesise using geothermal energy for a few thousand million years. So , business as usual for tube worms. Allan Mann Alnwick, Northumberland, UK
THIS WEEK’S QUESTION SWALLOW YOUR PRIDE
I’ve just seen a sword-swallowing act. Swords, seemingly longer than the depth from throat to anus were swallowed. It has to be a trick, doesn’t it? If it is, what’s the trick? If it isn’t, what’s going on? Alan Finnegan Whitehaven, Cumbria, UK