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Our latest collection - serious enquiry, brilliant insight and the hilariously unexpected Available from booksellers and at www.newscientist.com/ polarbears Do Polar Bears Get Lonely? THE LAST WORD Burn down the road During the last 100 years, humans have been burning oil, natural gas, peat and coal. In the next 50 years we will burn even more. Burning hydrocarbons produces carbon dioxide and water. How much has this water added to sea-level rise? n The cumulative amounts of oil and gas that have been used globally are not known with great precision but estimates published in 2007 in the International Journal of Environmental Technology and Management (vol 7, p 99) suggest that up to the year 2000 we had burned 110 gigatonnes (Gt) of oil, 60 gigatonnes of oil equivalent (Gtoe) for natural gas and 150 Gtoe for coal. “Oil equivalent” refers to the amount of oil that contains the same primary energy as a given amount of natural gas or coal, based on standard conversion factors, although these factors can vary according to the source of the fuel, particularly for coal. By converting the oil equivalent tonnages to actual quantities of the individual fuels we arrive at 110 Gt of oil, 47 Gt of natural gas and 250 Gt of coal. Assuming all the hydrogen in each of the fuels is oxidised to water, one can estimate that oil will generate 140 Gt of water, natural gas 105 Gt, and coal 90 Gt. Together that’s 335 Gt of water, which has a volume of 335 cubic kilometres. The surface area of all Earth’s lakes and oceans adds up to about 360 million square kilometres. Spreading the water of combustion evenly over this area would result in rises of about 0.95 millimetres. The journal also estimates that cumulative oil consumption would increase to 370 Gt for oil, 370 Gtoe for natural gas and 490 Gtoe for coal by the end of this century. This would lead to a total water level rise of about 4 millimetres. David Williams Watson, Australian Capital Territory Cauliflower cheese Why does exceptionally ripe brie cheese smell of boiled cauliflower? n The very question suggests criminal maltreatment of two delicately delicious comestibles. Be that as it may, smells may resemble each other for either of two reasons: because the volatile substances contain the same chemical components, or closely related chemicals; or because they contain unrelated chemicals with similar smells. For instance, traces of ozone, some halogens and some nitrogen oxides all smell much the same, though all are chemically different. The odours of your cauliflower and cheese are in any case complex mixes. The major components of both include organic sulphur-containing compounds, and nitrogen- containing compounds called amines. Like cabbage, cauliflower is a brassica, and its characteristic flavourings are isothiocyanates and related compounds that break down to produce various nitrogenous and sulphurous smells. Brassicas are also good sources of choline, which releases the notoriously smelly trimethylamine when decaying or over-boiled. Brie, like any other cheese, is rich in proteins. These are broken down by fungi in the cheese, and associated organisms, producing derivatives of amino acids that include sulphur-containing groups such as thiols and a whole zoo of amino compounds including, once again, trimethylamine. Such combinations might well smell reminiscent of overcooked brassicas. In suitable combinations, traces of such compounds are flavourings, but as the dying protests of abused delicacies, perhaps they can be more pungent. Jon Richfield Somerset West, South Africa This week’s questions A TANGLED WEB I heard recently that the UK’s Royal Society of Chemistry has set out to discover whether the old wives’ tale that spiders will not make webs on horse chestnut trees is true or false. If it is true, what could be the reasons for it? Mark Alberstat Halifax, Nova Scotia, Canada ON THE MARCH While on holiday in north-west France on the 25 March 2010 I came across the line of caterpillars shown in the photo below. They were on the seafront road in Carnac, heading towards the sea, maintaining close head-to- tail contact. The only vegetation between them and the sea was some raised flower beds. Can anybody identify these caterpillars and explain their behaviour? Bill Richardson Johnstone, Renfrewshire, UK Last words past and present, plus questions, at www.last-word.com
