The United Nations said the report, highlighting threats to creatures ranging from Australian butterflies to Spanish eagles, showed a need for the world to back the Kyoto protocol, meant to brake rising temperatures linked to human pollution.
\"A quarter of all species of plants and land animals, or more than a million in all, could be driven to extinction,\" said Chris Thomas, professor of Conservation Biology at England\'s University of Leeds.
Thomas, lead author of the study published in the science journal Nature, told Reuters that emissions from cars and factories could push temperatures up to levels not seen for one million to 30 million years by the end of the century, threatening many habitats.
The survey, the largest of its kind to date, studied global warming links to 1,103 species of plants, mammals, birds, reptiles, frogs and insects in South Africa, Brazil, Europe, Australia, Mexico and Costa Rica and extrapolated findings as far as 2050. It did not examine the oceans.
\"Climate change is the biggest new extinction threat,\" said Lee Hannah, a co-author, at Conservation International in Washington DC. Many species would simply be unable to adapt or migrate to new habitats.
Thomas said the feared extinctions could be one of the worst since the dinosaurs were wiped out 65 million years ago. \"This could be on a par with some of the geologically significant extinctions,\" he said.
Species under threat include many types of tree in the Amazon, the Spanish Imperial eagle and Boyd\'s forest dragon lizard in Australia. Birds like the Scottish crossbill could probably survive if only they knew to fly to Iceland.
U.N. studies project that global temperatures will rise by 1.4-5.8 degrees Celsius (3-12 F) by 2100, mainly because of human emissions of gases like carbon dioxide. Rising temperatures may spur more extreme weather like floods, heatwaves and tornadoes.
Thomas noted that some scientists argue that species have adapted to rapid climate change before -- as in a warming after the last Ice Age. But he said that humans had now taken over much of the planet, adding to pressures this time round.
Klaus Toepfer, the head of the U.N. Environment Program, said the report showed that extinctions could hit billions of people, mainly in the Third World who rely on nature for food, shelter and medicines.
\"This alarming report underlines again to the world the importance of bringing into force the Kyoto Protocol,\" he said.
Kyoto, which would rein in emissions of carbon dioxide, needs countries representing emissions of 55 percent of carbon dioxide to enter into force.
It has so far mustered 44 percent and cannot reach 55 without Russia\'s 17 percent, after the United States pulled out its 36 percent share in 2001, arguing it was too expensive and wrongly excluded poor nations. Moscow says it is undecided.
Thomas said the study estimated that 15-37 percent of all species could be pushed to extinction as a result of climate change to 2050 with a central assumption of about 24 percent. He urged a shift to new, cleaner energy technologies.