Letters archive

Articles espousing the meat-is-bad-for-the-environment point of view often assume that the meat is all from grain-fed animals ( 5 May, p 30 ). Those fed on pasture must have a lower carbon footprint, since this uses less chemicals, grain or supplemental water. Such farming largely uses land that would be unsuitable for arable crops. Yes, …

Niall Firth writes that "livestock graze on a quarter of our planet's ice-free land." Could all this land produce crops? Not my pastures. They support a stocking rate of only 2.8 hectares per "cow unit" – a 450-kilogram cow with late winter calf. Some US ranches must allow as much as 16 hectares. These cattle …

Simon Usborne discussed putting a value on trees ( 12 May, p 32 ). My experience of growing the pine tree Pinus radiata shows an interesting change in its value with age. At 20 years old, it has a market value of around A$20. Sold at 1 year old as a Christmas tree, its market …

Ray Reed suggests that if electric shock training collars for dogs are unacceptable, then perhaps electric fences for livestock are as well (Letters, 14 April ). However, the two cases are completely different. An electric cattle fence delivers discomfort that restricts the animal's movement in a predictable way. Like a scratchy hedgerow, an uncomfortable cattle …

Clare Wilson reports a "real life" test of the "trolley problem", in which subjects could allow five mice to receive a painful electric shock, or press a button to shock just one mouse ( 19 May, p 14 ). As in all cases of the trolley problem, the situation is so artificial that people try …

Vasectomy is the commonest form of contraception worldwide. True, those who take it up are not teenagers but men wanting "end of family" contraception. Still, it prevents more pregnancies than any other contraceptive method. I can understand the appeal of a male pill to men who want to avoid condoms, though it might be counterproductive …

Fred Pearce reports that developed nations expand their forests, while poorer nations lose them ( 19 May, p 6 ). Developed countries might well use less firewood, but surely that is because they have replaced firewood with fossil fuels, hardly much of an improvement. In any case, developed countries are beginning to use firewood on …

Colin Barras writes that dinosaurs were "reinstated as a scientific fact" in the 1980s ( 5 May, p 38 ). But in 1974 Robert Bakker and Peter Galton published "Dinosaur monophyly and a new class of vertebrates" ( doi.org/ftw3f9 ). This led to dinosaurs being widely accepted as a single distinct group. Almost all phylogenetic …

Your letters about the nature of time have been interesting. Rod Munday suggests that the future consists of events of which there are as yet no memories (Letters, 19 May ). But consider the future from the perspective of an observer just prior to the big bang. There was undoubtedly a future as a number …

You reproduce a widely circulated image of an emaciated polar bear limping across a barren landscape ( 10 February, p 35 ). I often wonder whether it simply shows an old animal near the end of its natural life. This by no means detracts from the importance of understanding and mitigating the effects of climate …