The main culprit for this change, they say in an article due out Thursday in the British journal Nature, is greenhouses gases, which are churned out by automobiles and industry and trap heat in the earth's atmosphere.

"An immediate and progressive switch to technologies that produce little or no new greenhouse gases, combined with active removal of carbon dioxide from the atmosphere, could save a million or more species from extinction," lead author Chris Thomas, a biologist from University of Leeds, said in a statement.

Thomas's team studied six regions rich in biodiversity, representing 20 percent of the planet's land area, and made projections for the survival of 1,103 species between 1990 and 2050, using elaborate computer models.

Three scenarios for expected climate change were used in the computer models -- a minimum expected rise between 0.8 and 1.7 degrees Celsius (1.4 and 3.1 degrees Fahrenheit) per year until 2050; a mid-range scenario with temperature increases of 1.8-2.0 degrees; and the maximum rise, when the Earth's average climes rise by over 2.0 degrees per year.

Australia, one of the regions studied, would lose over half of its more than 400 butterfly species by 2050, thanks to global warming.

Brazil's Cerrado area, a savannah-type area with a wealth of plant and animal species, could lose between 39 and 48 percent of its flora -- thousands of plants whose medical or scientific benefits will never be known.

The six regions studied by the scientists were Australia, Brazil, Costa Rica, Europe, Mexico and South Africa.

The head of the UN Environment Program, Klaus Toepfer, warned that "the figure of one million may be an underestimate", since it only counts the extinction of species due to climate change, without taking into account a "ripple effect" that could also kill off interdependent plants and animals.

Toepfer said humans would suffer from the consequences from global warning, the result of their dependence on fossil fuels.

"If one million species become extinct as a result of global warming, it is not just the plant and animal kingdoms and the beauty of the planet that will suffer.

"Billions of people, especially in the developing world, will suffer too as they rely on nature for such essential goods and services as food, shelter and medicines," he said.

Lee Hannah, a co-author of the study with the Washington-based Conservation International, said that species faced with a dangerously warm environment would naturally seek a cooler area, but this was no longer possible in many cases.

"If habitat destruction has already altered those habitats, the species will have no safe haven."

Not all of the million-plus species would disappear by 2050, Thomas said, but many would be in decline and en route to extinction.

The UN's Toepfer called the study an alarm which "underlines again to the world the importance of bringing into force the Kyoto Protocol", the international agreement to reduce greenhouse gas emissions which the United States has refused to adhere to.

TERRA.WIRE