The UN’s Cop28 climate conference has kicked off in Dubai this week – but one notable absence will be the US president. Joe Biden pledged to make the fight against climate breakdown one of his top priorities when he took office, and news of his absence from this year’s gathering has frustrated activists. Jonathan Freedland speaks to one such activist, Jerome Foster, who in 2021 became the youngest adviser to the White House when he was asked to sit on its environmental justice advisory council