Robin McKie's account of his 40 years as the Observer's science editor is as deeply absorbing as it is a warning to humanity ("What I've learned after 40 years as the Observer's science editor", Focus). He takes us back nearly 50 years to British glaciologist John Mercer's warning that continued use of fossil fuel could lead to a 2C temperature rise by the mid-21st century threatening, among other potential catastrophes, a 5m sea level rise. His warnings, since echoed by swelling numbers of scientists, point out that climate change "threatens to displace hundreds of millions of people from their homelands". Tragically, McKie reports, "large parts of society turn their heads and deliberately reject the truths that have been presented to them". Our increasingly busy roads and airports illustrate this. His article needs to be read by government ministers, reported widely in the press and studied in schools. Richard Vernon Oxford Everything on Earth is thermally driven, the warmer it gets the more dangerously active it becomes. So it is vital that we keep Earth's temperature within safe limits. In addition to net zero greenhouse gas emissions, we must achieve zero waste if we are to avoid rendering our planet home unsustainable. , so we are going to need all our philosophical wisdom and our best scientific achievement if we are to hang around much longer. John Stone Thames Ditton, Surrey This bill is a humane reform I have great respect for Sonia Sodha, so I took her notes of caution about the proposed assisted dying legislation seriously ("In the rush towards a law on assisted dying, the vulnerable have become expendable", Comment). My beloved partner of 40 years, Bob, died almost five years ago of cancer. He had the "decent end of life care" that Sonia argues should be the gold standard: he had palliative care from hospitals, district and Macmillan nurses. Nevertheless, he suffered greatly towards the end: medicine can't always magic pain away,…