Letters archive

Erle Ellis says formal recognition of an Anthropocene Epoch beginning in 1950 would be damaging in that it denies earlier human impacts. It does no such thing. Such impacts – from hunting, farming and urbanisation – go back through and characterise the 11,700 years of the Holocene (and some into earlier times). But they didn't …

Instead of using a 1950s sedimentary layer in a lake in Canada to define the start of the Anthropocene, I suggest that the appearance of lead in Greenland ice is, at least, a measurable and significant marker of our activity. Lead levels in Greenland ice became significant from 1000 BC, but they skyrocketed when leaded …

Your story on the breakdown of the water cycle states that one cup of coffee requires 140 litres of water to produce. I have tried to reverse-engineer this claim using rainfall data and crop yields, and this is only explicable on the basis that every drop of rain that falls on a plantation is somehow …

Glenda Dixon asked: "Why not use thermodynamic systems to get heat from the seas to generate electricity and heat local homes?" One reason is that the devices needed would be huge because their efficiency is low ( Letters, 26 August ). The only example that ever worked for any length of time was built by …

It has been suggested that the elongated interstellar object 'Oumuamua was sent to our solar system by advanced alien life ( 2 September, p 29 ). However, natural explanations seem more likely. Lava solidifying in a volcano conduit often takes up a rod-like 'Oumuamua shape. Erosion of the surrounding rock leaves the frozen lava as …

Reader Geoff Hammond might not see white roofs where he lives in the UK, but here in the US they aren't uncommon, or at least they are a choice. When having our roof reshingled a few years back, we opted for the whitest shingle available. The results are plainly visible in the view from Google …

Hammond suggests a lick of climate-friendly white paint on the roof. I did this about 30 years ago when my garage roof was replaced. It made a huge difference to the temperature in the garage, making it cooler in summer sunshine and less cold in winter. I agree – more people should do it. On …

Why is it so hard to define what is meant by ultra-processed foods (UPFs)? These comprise any edible substance made using ingredients not used by (or available to) home cooks, processed by methods not possible in home kitchens, or both of these ( 19 August, p 16 ). Incidentally, yogurt that is made in the …

With rivers polluted by sewage, frequent drought amid climate change, associated fish deaths, organic waste and low oxygen levels all adding to the woes facing UK rivers and other water bodies, natural measures to address the worst impacts are surely going to become of increasing importance ( 12 August, p 36 ). The argument for …

Annalee Newitz, who has had covid-19, says that US doctors are "leery of prescribing . No one is quite sure why." Perhaps the doctors have prior experience of this antiviral? It seems that it is effective at relieving symptoms and possibly in controlling infectivity, but there have been some reports of the virus rebounding after …