The saber-toothed cat, large ground sloth and other ice age giants of South America didn't go extinct solely because of climate change or prehistoric human activity, but because of a perfect storm of the two that hit the giant beasts at the same time, a new study finds.

For years, researchers have debated what felled many of the megafauna — animals that weigh more than 100 lbs. (45 kilograms) — shortly after the end of the last ice age. Some scientists blamed humans, who had newly colonized the Americas, while others pointed to the warming climate that followed the last ice age.

When it comes to confronting climate change, the world’s cities are proving that there’s strength in unity. The historic climate agreement reached in Paris in December, which was approved by nearly all of the world’s nations, was made possible in part by the progress that cities have made by working together.

Rich countries must ratify the climate change agreement reached in Paris last December, one of the world’s most at-risk nations has warned.

Support for strong action on climate change is at its highest level since 2008, with much sought after uncommitted voters showing the strongest support, according to Galaxy polling commissioned by the Climate Institute.

Rising temperatures are posing a threat to global food security.

The University of Cambridge has been criticized for not divesting from oil and gas companies, despite pressure from students and academics to do so.

The decision comes after a year in which the university has faced intense pressure on its fossil fuel investments which saw over 2,000 students sign a petition for divestment, while the students’ union council voted 33:1 in favor of divestment.

A group of business and academic leaders have bemoaned the “huge gap” between what experts say ought to be done to decarbonize Australia’s economy and the public’s willingness to accept such a policy.

They want Australia’s leaders to restart a conversation after the federal election about the need to transition the economy towards renewable and cleaner energy.

The United States, Canada and Mexico will promise on Wednesday to generate half their overall electricity from clean energy by 2025, the White House said.

"We believe it is an aggressive goal, but that it is achievable continent-wide," Brian Deese, senior advisor to US President Barack Obama, said Monday.

Climate change, habitat destruction, extinctions — the Earth has seen it all before, thousands of years ago. And humans may have been partly to blame for many of those changes in nature, too.

A new study published Friday in Science Advances shows that the arrival of humans in Patagonia, combined with a changing climate, led to the extinction of many species of megafauna about 12,000 years ago in the southern portion of what is now South America. The research offers a significant moment in the natural history of the continent: a definitive date of the mass extinction of megafauna — large or giant animals, like mammoths and giant sloths — in this part of the world. It also suggests a potential relationship between threatened species and climate change in our own time.

It is not news that Earth has been warming rapidly over the last 100 years as greenhouse gases accumulate in the atmosphere. But not all warming has been happening equally rapidly everywhere. Temperatures in the Arctic, for example, are rising much faster than the rest of the planet.

Patrick Taylor, an atmospheric scientist at NASA's Langley Research Center in Hampton, Virginia, says that one of the main factors for the Arctic's rapid warming is how clouds interact with frozen seawater, known as sea ice.