The sun, beating down on tropical waters, powers the weather systems of the globe. Moisture evaporates from the warming ocean and rises to create great storms. The winds generated out at sea sweep inland across the continents. As they travel across the Sahara they create the biggest of all sand storms blowing sand halfway round the world to fertilise the Amazon jungle. Winds blowing across the Indian Ocean collect moisture and sweep northwards towards the Himalayas. As the air rises, so it cools. The water it carries condenses into clouds and then falls as the life giving rains of the monsoon. So air currents powered by the sun carry wet air to the middle of continents. Without water there can be no life, but its distribution over the land is far from even. Deserts cover 1/3 of the land's surface and they're growing bigger every year.


直射热带海域的太阳是地球气候系统的动力。湿热的空气从温暖的海洋中升起，形成巨大的风暴。从海洋上产生的大风，过海跨洲，进入内陆。它们吹过撒哈拉时，引发世界上最大的沙尘暴，这些尘土越过半个地球，给亚马逊丛林带来养份。经过印度洋的海风带着湿气向北吹去，一直吹向喜马拉雅山，空气在上升的过程中温度会下降。它携带的水份凝结成云，然后变成给大地带来生机的季风雨。这样，由太阳提供动力的气流把湿润的空气带到了各个大陆的中央地带。没有水就没有生命，但水在陆地上的分布却极不均衡。沙漠占陆地面积的1/3，而且这一面积每年还在扩大。