Pessimism is probably “a bigger problem than climate change”, said the novelist Ian McEwan on Monday afternoon, as temperatures broke May records in the UK. McEwan “constantly” hears people say that they don’t “expect their children to have as good a life as they did”, but suggested that optimism is a “moral duty”. McEwan’s latest book, What We Can Know, is partly set in 2119, in a Britain submerged by seas. He spoke at the Hay festival on a panel alongside the former NFU president Minette Batters and Sandi Toksvig, on a day that saw temperatures in London reach 34.8C, beating a May record set in 1922. McEwan went on to say that optimism is an “exercise in rationality”, because it’s “quite possible” – given that “the world is big, cultures are diverse” – that “there could be a revolution happening and we don’t even know about it”. He referred to the “historical moment” in 2020 when electricity generated from renewable sources outpaced that generated from gas and coal plants in the UK. “We were …