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Urban trees planted in Stockholm, Sweden, have been shown to be healthy, and the methods used are now being applied in the UK with growing success. The Stockholm Tree Pit system captures rainwater from roofs and roads, then channels it into a tree pit containing crushed granite and biochar. This allows for ingress of both …

Fallen leaves from urban trees are often swept up and disposed of by street cleaners or residents, removing a valuable source of leaf litter, which forms the top layer of soil in forests or woodland. Returning this as a mulch, in addition to added topsoil, could help solve some of the problems you report. In …

You rightly laud South Australia's push to decarbonise its electricity generation, but, in common with so much reporting around net zero, the implication is that we will hit this target when all of our electricity generation is carbon-free. Global primary energy consumption in 2022 was around 179,000 terawatt-hours, of which about 137,000 TWh, or 82 …

S. W. Shaw calculates that around 9 million UK homes may have converted to using heat pumps in the next 15 years. However, millions of homes here are Victorian and broadly aren't suitable for heat pumps . Beyond those 9 million conversions, to really make progress towards net-zero housing, we may have to bulldoze all …

There have been welcome ideas from readers relating to carbon taxes, but an important added ingredient is needed to make them work, to prevent "carbon leakage" via the import of goods with high embedded carbon ( Letters, 21 October ). To that end, the European Union has created the Carbon Border Adjustment Mechanism (CBAM). It …

I am concerned about the impression that discarded toys generate more e-waste than vapes. While it is true that toys make up the majority of this in landfill, I suspect vapes make up the majority outside landfill and fly-tipping sites. Some ex-smokers discard them like cigarette butts ( 21 October, p 14 ).

You raise the idea that there may be a harder core to the Great Sphinx of Giza, the shape of which was formed by wind erosion ( 4 November, p 13 ). Couldn't this question be easily answered by the use of ground penetrating radar? If there is no hard core, then the riddle remains!

Matthew Sparkes rightly urges governments to speed up putting detail on legislation and regulation to ensure the safe and responsible development of AI. But we shouldn't only worry about this aspect ( 11 November, p 11 ). Where AI is already safe and responsible, we need to speed up its deployment and impact, as it …

Last time I checked, our theories of the universe would be down the tubes if anything could truly break Newton's third law of motion, aka the conservation of momentum ( 28 October, p 14 ). The idea that sperm can do so reminds me of previous assertions that bumblebees violate the laws of aerodynamics . …

Researcher Eske Willerslev found Borrelia recurrentis to be the second-most widespread of human zoonotic pathogens during millennia of our history, behind only the plague bacterium. This sets a concerning precedent for other pathogens that originate in animals ( 28 October, p 8 ). In 1982, when Lyme disease was found to be caused by another …