May 21 (Reuters) - May 22 is the U.N.'s International Day for Biological Diversity, focused in 2007 on how global warming may drive many species of animals and plants to extinction.

Following are facts about the diversity of life on earth:

* Scientists have no clear idea of how many species -- from algae to blue whales -- live on earth. Estimates range from about 5 to 100 million. There are about 1.8 million named species so far.

* Humans are responsible for the worst spate of extinctions since the dinosaurs were wiped out 65 million years ago, according to a U.N. report in March 2006. It blamed destruction of habitats, expanding cities, pollution, deforestation, global warming and the introduction of "invasive species".

* "Climate change is forecast to be become one of the biggest threats to biodiversity," the U.N. Convention on Biological Diversity said in a statement marking May 22.

* "Approximately 20-30 percent of plant and animal species assessed so far are likely to be at greater risk of extinction if increases in global average temperature exceed 1.5 to 2.5 Celsius" (2.7 to 4.5 Fahrenheit), according to a report in April 2007 by the U.N. climate panel. Beyond that, it said ecosystems would face ever more wrenching changes.

* World leaders agreed at a 2002 U.N. summit in Johannesburg to "achieve by 2010 a significant reduction of the current rate of biodiversity loss at the global, regional and national level as a contribution to poverty alleviation and to the benefit of all life on earth."

* A global "Red List" of endangered species documents about 800 extinctions since 1500, from the flightless dodo to the Golden Toad of Costa Rica. Experts believe the real number is far higher.

* About 12-13 percent of the world's land area is in protected areas but only about 0.5 percent of the seas.

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