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The Tropics dominate world weather by producing a strong updraught of warm moist air which cascades out towards the poles.

The area generating the updraught has been expanding since 1979 by 0.5 degrees- 1 degrees latitude per decade.

I lay on my chest under the pilot's seat, and pushed to the right a little wooden door, which slid away from a rectangular hole in the floor through which came a swift updraught of wind.

Under the equator, owing to the fact that the sun for a considerable belt of land and sea maintains the earth at a high temperature, there is a general updraught which began many million years ago, probably before the origin of life, in the age when our atmosphere assumed its present conditions.

Trades and counter trades would doubtless exist but for the efficiency of this updraught, which is caused by the condensation of watery vapour, but the movement would be much less than it is.