Â鶹´«Ã½

Michael Le Page notes that using air conditioning in response to climate change produces yet more heat ( 4 August, p 18 ). But there is a useful alternative to the refrigeration method: evaporative air conditioning. The effect was used by the ancient Egyptians, who wafted, or had slaves waft, a current of air over …

Is Ian Angus saying that it is morally wrong to seek a lower human population as we combat climate change ( 25 August, p 22 )? In the Scientists' Warning to Humanity , first issued in 1992 and repeated in the journal BioScience in 2017 , the majority of the then-living Nobel laureates signed up …

Clare Wilson suggests buying another freezer to guard against food shortages in case of a Brexit disaster ( 4 August, p 21 ). This may not be helpful. If the UK crashes out of the European Union with no deal, it is probable that the pound will similarly crash against the euro and dollar. Oil …

Howard Bobry takes his local emergency preparedness meeting to task for assuring him that a discharged alkaline battery weighs less than a fresh one (Feedback, 7 July ). But as Paul Hewitt notes in his textbook Conceptual Physics , a change of energy of any object at rest is accompanied by a change in its …

Erik Foxcroft suggests using vacant glacial valleys as water reservoirs for pumped storage hydropower (Letters, 18 August ). By the time the glaciers have retreated enough to make this viable I think it will be a bit too late to think about such storage.

Paul Whiteley suggests that instead of funding large-scale energy projects we should spend the money putting solar hot water panels on people's roofs (Letters, 4 August ). We have solar hot water panels on our roof, and they have saved us money for some years. But our predominant use of warm water is to wash …

Thank you for the interesting article on allergies ( 11 August, p 28 ). I was amazed, though, to find no discussion of whether stress levels can have a role, either as a precursor of allergic reactions or in exacerbating them.

Penny Sarchet doesn't mention a factor that, I am sure, contributes to allergies: stress. I refer to unrelenting mental stress to which there is no conceivable ending or solution. I am sure, for example, that at least some children who develop an allergy after starting school are the targets of bullying.

I was surprised to read that "we" (whoever that might be) have ever dreamed of converting Mars into an Earth-like world ( 4 August, p 6 ). No one – surely – has ever really proposed this as a practical possibility, outside the realms of science fiction. Have they?

. Chris Milligan warns that much of the world is in for a rough ride from climate change (Letters, 4 August ). This is timely, given the drought gripping New South Wales as I write. What isn't timely is the response of the Australian government. As usual it is dispensing vast amounts of "drought relief" …