Famed British naturalist Sir David Attenborough, while speaking at an international climate conference Monday in Poland, warned that climate change could lead to a "collapse of our civilizations and the extinction of much of the natural world."

The 92-year-old TV presenter blamed humans for the “disaster of global scale, our greatest threat in thousands of years.”

The United Nations' conference, known as COP24 (the informal name for the 24th Conference of the Parties), is an annual gathering of the world's top experts on climate change.

Also speaking at the conference, the head of the U.N. didn't have many encouraging words, either: “Even as we witness devastating climate impacts causing havoc across the world, we are still not doing enough, nor moving fast enough, to prevent irreversible and catastrophic climate disruption,” U.N. Secretary-General Antonio Guterres told the thousands of delegates from almost 200 countries who gathered in the city of Katowice, Poland.

More:U.S. impacts of climate change are intensifying, federal report says

"We need a complete transformation of our global energy economy, as well as how we manage land and forest resources," Guterres said. "We need to embrace low-carbon, climate-resilient sustainable development."

Preventing “dangerous” human interference with the climate system is the ultimate goal of the annual conference.

More:U.N. says 2018 will be Earth's 4th-warmest year on record, predicts a 5- to 9-degree temperature rise this century

Recent reports from the U.S. and the U.N. continue to sound the alarm about the urgency of the problem. The U.S. report said the impacts of global climate change are already being felt and are projected to intensify in the future, while the U.N. said that 2018 is expected to be the fourth-warmest year on record for the Earth.

Burning fossil fuels such as oil, gas and coal are responsible for warming the planet's atmosphere and oceans over the past century and a half.

By the end of the conference next week, it’s expected that countries will reach an agreement on a number of goals outlined in the Paris Agreement, which goes into effect in 2020, the Nature Conservancy said.

Contributing: The Associated Press