What a wonderful world! Of course, some parts of it are more amenable than others. Not everywhere is as idyllic as King Arthur's Avalon, where
On either side the river lie
Long fields of barley and of rye
That clothe the wold and meet the sky
And thro' the field the road runs by
To many-tower'd Camelot.
Indeed, there are places like Antarctica and the barren wastes of the Russian tundra that one could very definitely take or leave. By and large, however, this planet of ours is a nicely suited place for life. The temperature and pressure are just right; the air is breathable; and a benign atmosphere shields us from the worst effects of ultra-violet radiation.
It is quite different, for example, from Venus, where conditions are too hot for life, and Mars, which is too cold. Distance from the Sun plays an important part, but the temperature of each planet is also regulated by the strength of its greenhouse effect, and in the case of Earth, the balance - for the present - is exactly right.
How, one might ask, did this happy situation come about? Traditionally, there are two answers. One approach is that evolution has enabled life on Earth to adapt in the way best suited to any environment in which it finds itself.
A complementary view has it that life has altered the environment to suit itself. Plants, for example, absorb carbon dioxide by means of photosynthesis and create oxygen, while animals and humans survive by the reverse process: by this delicate relationship, and many others, life alters the composition of the atmosphere to achieve the conditions needed for survival.
A controversial philosophy called the Gaia Hypothesis goes further and tries to link the two. The name comes from Gaia, the goddess of the ancient Greeks who symbolised our "Mother Earth", and the theory postulates a symbiotic bond between life itself and the environment in which it exists. Gaia suggests that life and the atmospheric environment are closely linked parts of a whole system - a system with elaborate feedback mechanisms which dictate the way in which the whole planetary scene evolves.
Supporters say that this combined system has developed in such a way that it can regulate and repair itself. If it is knocked off balance by catastrophic events, or by more gradual - even human - influences, it can repair the damage, and life, although not necessarily any individual species, will survive. It means that life as a whole is very robust - and may even be immortal. So why, taking this broader view, should we worry about global warming?