produce oxygen, the oxygen mixes with hydrogen to produce rain. In photosynthesis trees also produce some hydrogen as a by-product so virtually they can make rain. (Although it actually takes more time). 150 years ago there were many more trees. Botanists have observed from tree ring growth, that there was 30% more oxygen, as well. Put 2 + 2 together. The desertification of the planet has caused global warming. WE need oxygen and rain to survive. The countries with the most water are Brazil, Russia and Canada: they also have the most trees.....