On the starting point for a new geological epoch (1)
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 鈥� from hunting, farming and urbanisation 鈥� go back through and characterise the 11,700 years of the Holocene (and some into earlier times). But they didn’t disrupt the overall stability of the climate, sea level and biosphere (9 September, p 21).
The Anthropocene as a potential new geological epoch represents something quite different: a marked and rapid change from the relative stability (sustained over millennia) of the Holocene into another planetary state, one of sharply disrupted global chemical cycles, intensifying global warming, a reconfigured biosphere and countless globally dispersed novel materials, including pesticides, plastics and artificial radionuclides.
Driven from the mid-20th century on by industrialisation, technological advance, population growth, fossil fuel burning and globalisation, this change is indelibly imprinted into recent geological deposits. Much is now irreversible: the planet has no way back to a Holocene state.
This Anthropocene concept has a coherence, reality and significance that justifies formalisation, to stabilise its meaning and use in communication. To obfuscate the meaning of this recent planetary change by hiding it within all human impacts through all time, rather, would damage science.
On the starting point for a new geological epoch (2)
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 fuel was introduced and became widely used in the 20th century.
Thirsting for truth on water-gobbling crops (1)
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 taken out of circulation. Clearly, it isn’t (26 August, p 36).
Coffee is a crop like any other, and some of the rain that falls will be taken up by the bushes and transpired (so is still in the water cycle) and the rest will run off into streams and rivers. Since all we are harvesting are the “cherries” 鈥� the bushes are perennial 鈥� what we are taking out of the system is tiny. We would take out more by growing cabbages, as we eat the whole thing.
Thirsting for truth on water-gobbling crops (2)
You say it takes 12,651 litres of water to produce 100 grams of vanilla beans. Clearly that doesn’t all end up in the beans. Surely at least some ends up in the atmosphere or in groundwater.
More reasons not to get power from ocean warmth
Glenda Dixon asked: “Why not use thermodynamic systems to get heat from the [warming] 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 Japan for the island nation of Nauru. . Of that, 90 kW were used to run the device. It relied on a mixture of water and ammonia, which poses a significant environmental risk if it leaks out.
'Alien object' could just be a volcanic plug
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 a volcanic plug. ‘Oumuamua could have formed like this on a distant planet. A later collision with another object could have ejected the plug into space. Or the close pass of its planet to a star may have increased the temperature and pressure of magma so much that it fired a rod of frozen lava upwards from a volcano fast enough to escape from a small planet.
The white roof fan club is getting bigger (1)
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 Earth. Our attic has stayed much cooler since the reroofing (Letters, 2 September).
The white roof fan club is getting bigger (2)
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 鈥� more people should do it. On a flat roof, nobody would really notice, so they would be unlikely to complain!
If you can't make it at home, it's ultra-processed
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 traditional way is most definitely not a UPF, and I don’t think it should have been used to illustrate the story.
What lies beyond the Zone of Utter Ignorance?
I would like to make a change to cartoonist Tom Gauld’s diagram of knowledge. Beyond the “Zone of Utter Ignorance” 鈥� in the interests of topicality and with half an eye on the future 鈥� should be added the “Event Horizon of Conspiracy Theory” (2 September, p 47).