<P> No longer do we have to justify the existence of humid tropical forests on the feeble grounds that they might carry plants with drugs that cure human disease . Gaia theory forces us to see that they offer much more than this . Through their capacity to evapotranspirate vast volumes of water vapor, they serve to keep the planet cool by wearing a sunshade of white reflecting cloud . Their replacement by cropland could precipitate a disaster that is global in scale . </P> <P> During the last century, decreases in biodiversity have been increasingly observed . In 2007, German Federal Environment Minister Sigmar Gabriel cited estimates that up to 30% of all species will be extinct by 2050 . Of these, about one eighth of known plant species are threatened with extinction . Estimates reach as high as 140,000 species per year (based on Species - area theory). This figure indicates unsustainable ecological practices, because few species emerge each year . Almost all scientists acknowledge that the rate of species loss is greater now than at any time in human history, with extinctions occurring at rates hundreds of times higher than background extinction rates . As of 2012, some studies suggest that 25% of all mammal species could be extinct in 20 years . </P> <P> In absolute terms, the planet has lost 52% of its biodiversity since 1970 according to a 2014 study by the World Wildlife Fund . The Living Planet Report 2014 claims that "the number of mammals, birds, reptiles, amphibians and fish across the globe is, on average, about half the size it was 40 years ago". Of that number, 39% accounts for the terrestrial wildlife gone, 39% for the marine wildlife gone and 76% for the freshwater wildlife gone . Biodiversity took the biggest hit in Latin America, plummeting 83 percent . High - income countries showed a 10% increase in biodiversity, which was canceled out by a loss in low - income countries . This is despite the fact that high - income countries use five times the ecological resources of low - income countries, which was explained as a result of process whereby wealthy nations are outsourcing resource depletion to poorer nations, which are suffering the greatest ecosystem losses . </P> <P> In 2006 many species were formally classified as rare or endangered or threatened; moreover, scientists have estimated that millions more species are at risk which have not been formally recognized . About 40 percent of the 40,177 species assessed using the IUCN Red List criteria are now listed as threatened with extinction--a total of 16,119 . </P>

What do you mean by biodiversity in hindi