The Intergovernmental Panel on Climate Change has repeatedly warned that allowing global temperatures to increase by 1.5C above pre-industrial levels would have a devastating and irrevocable impact on our climate. But what, theoretically, would happen to Earth if the planet were to cool by the same amount? Simon Salter, Flintshire Post your answers (and new questions) below or send them to nq@theguardian.com. A selection will be published next Sunday.