How seriously should we take global warming? By most accounts, very seriously indeed, especially as there seems to be a critical tipping point at which the whole process takes on a greater velocity. Quite when that tipping point is reached won't be clear until after the event - but that doesn't mean it's not coming, like the giddy moment at the top of a roller coaster....

From memory, here are two items that worry me about the way global warming is set to escalate:-

i) sheets of (white) ice are great reflectors of heat, but the more they reduce, the more they are replaced by areas of (dark) land and sea. As we all know from secondary school, dark colours are good absorbers of heat, so the warmer the planet gets, the more solar heat it will absorb.

ii) the permafrost, that permanently frozen subsoil across Canada and Russia, is beginning to thaw. Unfortunately for us, there are unknown quantities of methane gas locked in the subsoil. In Canada they are studying the methane which is now bubbling up in marshes and swampland which, within living memory, were frozen solid all year round. The double bad luck is that methane has a powerful greenhouse-gas effect, so the warmer the planet gets, the more solar heat it will trap.