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Graham Lawton can count me as a staunch fan. I agree with him that it is self-deception to imagine that he offset much, if anything, of his flight-related carbon dioxide by crossing a greenwashing scheme with a tiny piece of silver. This doesn't mean it is impossible ( 11 May, p 22 ). I fly …

Has Lawton considered that his carbon offset certificate's "1.69 mt" might actually be a correct use of the prefix "m" and mean that he has paid to offset 1.69 millitonnes of carbon? He could probably do a better thing for the environment if, instead of paying into a rather opaque "carbon offset" market, he visited …

You report the end of the Bronze Age in the eastern Mediterranean 3200 years ago has generally been characterised by its short duration of 50 years, mass migration of populations such as the Sea Peoples and abandonment of cities. In my view, the Sea Peoples were pushed out of their homes by plague etc. The …

Jan Zalasiewicz implies that the mass of evidence of human impact on the Earth system was rejected in the recent vote by geologists over the Anthropocene. Actually, few scientists would dispute that substantial body of evidence. What was rejected was the specific proposal that the start of the Anthropocene epoch should be placed in 1950 …

Name and address supplied Thank you for David Ropeik's excellent and, for me, timely article on cancerphobia. I have just undergone treatment for breast cancer, including surgery and radiotherapy. I have deliberately limited the people who know, specifically because I couldn't face inaccurate, exaggerated, even hysterical responses. I am still working out how I might …

In your look at whether climate change is accelerating after a record year of heat, you cite models that predict a speeding up due to underestimates of the loss of the cooling effect of some pollutants. These are in decline as clean air policies take hold ( 11 May, p 14 ). The contribution of …

Katie Steckles's article about "Pythagoras in the wild" reminds me of an interesting experience of encountering maths when buying cake tins. I got two "catering-sized" square ones from a commercial baking supplier. I was intrigued by the dimensions: about 360 millimetres per side. That figure didn't seem to mean anything special. Neither did the equivalent …

Several readers have voiced optimism about reaching a new economic equilibrium in a world where each generation is smaller than the previous one ( Letters, 20 April ). However, such an equilibrium would be only temporary. Once the world population falls to, say, half a billion, no one is building a new particle collider or …

How feasible are Dyson spheres, signs of which may have cropped up in a survey of 5 million stars in our galaxy? The basic engineering logic behind these proposed alien structures that encircle a star to capture all its energy isn't obvious ( 18 May, p 12 ). It makes sense that you would start …

The ridiculous idea of a Dyson sphere is truly a waste of space. Any industrial beings even 500 years in advance of us would have solved any energy needs without resorting to this silly and clumsy idea. Even our own struggles to develop fusion power in order to boil water to make steam to drive …