Guardian: Scientists use a variety of approaches to estimate the Earth’s climate sensitivity – how much the planet will warm as a result of humans increasing greenhouse effect. For decades, the different methods were all in good general agreement that if we double the amount of carbon dioxide in the atmosphere, Earth’s surface temperatures will immediately warm by about 1–3°C (this is known as the ‘transient climate response’). Because it would take decades to centuries for the Earth to reach a new energy…