Five billion people will experience extreme climates before 2050 if carbon emissions are not curbed and continue at their current rate, scientists have said.
Published in the journal Nature, researchers from the University of Hawaii have said their shocking results indicate that the world's climate will have changed beyond recognition within a generation.
Using data from 39 Earth System Models developed by 21 independent climate centres in 12 countries, the team provided an index showing when climates across Earth will shift outside the most extreme records experienced over the last 150 years.
"The results shocked us. Regardless of the scenario, changes will be coming soon. Within my generation, whatever climate we were used to will be a thing of the past," said lead author Camilo Mora.
They found that under a "business-as-usual scenario" where emissions are not reduced, the planet will experience a radically different climate by 2047. If greenhouse gas emissions are stabilised this will be pushed by back to 2069.
According to the study, the tropics will be the first area to experience the effects of climate change and will be badly affected with species unaccustomed to climate variability.
Ken Caldeira of the Carnegie Institution for Science's Department of Global Ecology, said species will either have to move to find suitable climates, adapt or go extinct: "This work demonstrates that we are pushing the ecosystems of the world out of the environment in which they evolved into wholly new conditions that they may not be able to cope with. Extinctions are likely to result.
"Some ecosystems may be able to adapt, but for others, such as coral reefs, complete loss of not only individual species but their entire integrity is likely."
Looking at the impact on humans, the researchers say in an "optimistic scenario" one billion will experience extreme climates before 2050, with this number reaching five billion if emissions are released at their current rates.
They predict the climate changes will lead to shortages of food and water, spread of infectious diseases, increased conflicts and economical challenges.
Our results suggest that countries first impacted by unprecedented climates are the ones with the least capacity to respond," said co-author Ryan Longman. "Ironically, these are the countries that are least responsible for climate change in the first place."
The authors say their study suggests any effort to slow climate change will require a bigger commitment from developed countries and more extensive funding for social and conservation programmes in developing countries.
"Scientists have repeatedly warned about climate change and its likely effects on biodiversity and people," said Mora. "Our study shows that such changes are already upon us. These results should not be reason to give up.
"Rather, they should encourage us to reduce emissions and slow the rate of climate change. This can buy time for species, ecosystems, and ourselves to adapt to the coming changes."