Jason DeCrow/CP Former U.S. President Barack Obama accepts the Robert F. Kennedy Human Rights Ripple of Hope Award at a ceremony in New York on Dec. 12, 2018.

CALGARY — Former United States president Barack Obama says failure to transition to cleaner energy sources would lead to global chaos that would be hard to reverse, but he's optimistic fossil-fuel-centric economies such as Alberta's can make the necessary changes. Obama spoke Tuesday to a near-full arena in Calgary, home to several oil and gas company headquarters that are replete with empty office space due to a years-long industry downturn. "All of us are going to have to recognize that there are trade-offs involved with how we live, how our economy is structured and the world that we're going to be passing on to our kids and grandkids. Nobody is exempt from that conversation," Obama said. He said fossil fuels have provided a cheap and plentiful source of energy since the Industrial Revolution. The remark drew a loud whistle and applause from the audience.

Dwayne Larson/CP Obama and Michael Burns, CEO of the Princess Margaret Cancer Foundation, shake hands at the Bell MTS Centre, in Winnipeg on March 4, 2019.

The crowd also clapped when Obama said there is indisputable science that the planet is getting warmer. "It is indisputable that although we can't ascribe any particular kind of weather event to rising temperatures, that at the current pace that we are on, the scale of tragedy that will consume humanity is something we have not seen in perhaps recorded history if we don't do something about it." Rising oceans will displace populations from coastal areas and climate change is also having an impact on the prevalence of insect-borne diseases, he said. "Moose right now (have) to deal with tick-borne diseases that they didn't have to do 10, 15 years ago. I really like moose. I assume Canadians, you, do too," Obama said. "These are just facts." He said the question becomes how to build recognition, not just generally but in places such as Alberta, that newer energy sources need to be developed and older ones have to be cleaned up. Obama said the chaos wrought by global climate change will make politics more toxic. Watch: People lined up to see Obama in Winnipeg. Story continues below.