Climate change will result in a massive shift in the Earth's vegetation by 2100 when the world's greenhouse gas emissions will have doubled, a new study predicts, based on a computer model of the next three centuries.

This vegetation change may cause animals to migrate with the plants, and those that cannot adapt to the new climate may simply go extinct, the study said.

The research projects the biggest shift in the world's plant life this century will occur in the far Northern Hemisphere, particularly in the boreal forest. It also forecasts that most land areas not covered by ice or desert will see a dramatic change in their mixes of plant and tree species with "hotspots" in the Himalayas and Tibetan Plateau, the Mediterranean, eastern equatorial Africa, southern South America, the Great Plains and the Great Lakes.

Researchers at NASA and the California Institute of Technology based their findings on the output of a computer model of vegetation change over the next three centuries under the "middle of the road" greenhouse gas emissions scenario developed by the Intergovernmental Panel on Climate Change, which assumes that the world's greenhouse gas emissions will double by 2100.

The computer model showed that climate change will alter the mix of vegetation on 49 percent of Earth's land surface by the end of this century, changing existing ecosystems. The changing climate will also convert 37 percent of the world's land ecosystems from one type, such as tundra, forest or grassland, into another by 2100, researchers said.

The study's lead author, Jon Bergengren, said the vegetation shifts will most threaten animals and insects that have evolved to live among particular plant species.

"Animals that are dependent on plants will either have to migrate with the plants, if the plants can successfully migrate, or hang on with plants that are struggling to survive," said Bergengren.

Bergengren said that widespread human development can, however, complicate and in some cases prevent plants and animals from migrating to new habitats as climate change alters existing ecosystems. "A lot of times, when a plant or animal wants to migrate, it runs into a monoculture agricultural zone, or it runs into a city," he said.

Not all plant species in an ecosystem will react the same way to climate change as some may be more able to adapt to the new climate than others. Some species may migrate to a new area as current climate zones shift poleward, while those that cannot adapt may go extinct, according to the study.

The study was published by the journal Climatic Change.