ANYONE who has experienced the privilege of flying has probably been captivated by the scale of the Earth.
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Flying over thousands of kilometres of land, replete with large swathes of forests and the signs of human industry like roads, farms and settlements, it can appear that the Earth is so big, how could the activity of humans ever affect the climate?
We are like the flea on a dog, unable to alter the course of the dog but subject to the occasional life-threatening scratch!
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But if the flight attendant opened the door we would soon die. Not from being sucked out of the aircraft, but simply because there is not enough oxygen in the air at that height to keep us alive.
In fact, the breathable atmosphere only extends above our heads for about seven kilometres. That's about the distance from Bathurst to the airport or slightly longer than the Mount Panorama racetrack.
Seventy five per cent of the entire atmosphere is within 11 kilometres of the ground and at 15 kilometres, the air is too thin to fly most planes.
Interestingly, the ozone layer from 15 to 35 kilometres consists of 10 parts per million ozone molecules (0.001 per cent), which is still enough to shield us from the solar radiation which would otherwise obliterate humanity.
For many people, it is hard to conceive that human activities could influence Earth systems, which have always been operating and always will, causing constant changes to the biosphere.
My view is that it's hard to find any place or any natural process that humans haven't had an impact on!
We have certainly been responsible for changing the composition of our atmosphere with enough nitrous and sulphurous oxides to cause acid rain, enough carbon dioxide to acidify the ocean, enough chlorofluorocarbons to create a hole in the ozone layer, enough nuclear dust to raise the level of radiation on the Earth's surface to an all-time high and now, enough greenhouse gases to act like a doona around the planet, making it warmer.
Maybe it's time to tread a bit more carefully.