TORONTO -- A new study suggests that climate change likely drove North America鈥檚 megafauna to mass extinction, rather than overhunting, as researchers previously believed.

Instead, the new modelling report suggests that the population of large exotic mammals rapidly declined approximately 13,000 years ago in response to a drastic drop in temperatures.

The study suggests the large creatures such as mammoths, giant beavers and dwelling sloths 鈥� weighing up to 44 kilograms 鈥� had all disappeared due to temperature shocks.

鈥淚ncreased atmospheric CO2, which is known to reduce plant nitrogen content, may have led to poorer quality forage and reduced landscape carrying capacities. And in some regions, major vegetation changes in response to climate change were so rapid that megafauna populations may not have had time to adapt,鈥� the study reds.

During the time of this specific extinction there were two major climatic events, one of which was an ice age that led researchers to their previous beliefs about what killed off the animals. 

Researchers have heavily debated the cause for the megafauna鈥檚 mass extinction since the 1960s, primarily arguing that overhunting was the driving force in this mass extinction, similarly to many other animals that were hunted to extinction. 

The theory was that because the human population immensely grew approximately 14,000 years ago, hunters preyed on these large animals, while the species did not possess the defensive behaviour they needed to defend themselves against weapon dwelling humans.

Scientists have also disputed this claim, arguing there is little archeological research to suggest that hunting was widespread enough to actually cause an extinction and there is little physical evidence to back up the relationship between the two, leading scientists to believe that climate may have played a role.

鈥淎lternatively, climate change may have indeed been the primary driving force behind the extinctions, with humans playing no significant role, or perhaps at most performing a coup de grâce on megafauna populations already heading towards extinction,鈥� the study reads.

Other studies suggest that the population fluctuated as the climate changed.

Despite the fact that humans may not have played a direct role in the disappearance in megafauna, the report says there is no denying the relationship between climate change and mass extinction.

鈥淢egafauna populations levels could, for example, have generally increased along with temperature, giving rise to the relationship we identified, but then crashed in response to rapid temperature shocks that crested some currently unidentified eco-biological threshold,鈥� it reads.