Astronauts often say is that looking down on this planet from space makes them realise just how small and fragile the Earth really is. It forces them to question humanity's relentless exploitation of natural resources, its violent and destructive wars and the sheer greed that apparently drives us on.

Not all of us can be astronauts, but Google Earth can have a similar effect. When you first see that blue globe all alone against the dark background, it's shocking how small and forlorn it appears.

Zoom into your home town, then scroll across to another city, maybe another country. You note that it takes just a few seconds to move across, and also that almost all of the land underneath you contains human settlements; often large, sprawling cities that look a bit like mould growing over fruit.

If there were ever any doubts that human activity is changing the planet - and changing it for the worse - this view of Earth should dispel them completely. When 49 percent of plant species are endangered, along with 30 percent of fish, 24 percent of mammals, 25 percent of reptiles and 12 percent of birds, any self-delusion about human-induced environmental disaster is pointless.

I've written previously about the excessive power consumption of PCs and other electrical equipment, but there's another way in which such things are destructive; their life-cycles are so short that many are discarded just months after being bought.

This wastes the energy involved in their creation and the raw materials that are finite in their availability, and may also release toxic materials such as heavy metals into the environment.

It doesn't take much effort to make a difference, though. If you were given a new mobile phone for Christmas, don't just throw the old one in the bin. Ask your local council about recycling (and don't let them fob you off - they have a responsibility to try), or talk to local charities, as many of these will take old mobile phones for recycling or re-use.

Old computers can be more difficult to dispose of safely, but again there are charities that make use of old PCs. Just because a machine can't run Windows Vista doesn't mean it's not useful. There are some excellent operating systems that will run on old PCs - even ten year old machines - such as Puppy Linux.

Don't let the "bigger, better, faster, more" mentality blind you: after all, that PC you now think is junk was once the fastest machine you could buy. It'll still be useful to someone.

If this recycling effort makes you feel good, that's great. How about taking a few more steps? Try buying food locally and/or from sustainable sources, or maybe insulating your home, switching your electricity account to a 'green' energy provider, moving your accounts to an ethical bank, avoiding supermarkets that use excessive packaging, flying less, driving less... the list goes on.

Ultimately these small changes add up. You won't change the world on your own; nobody can do that. But for a small effort you can be part of the solution instead of being part of the problem.