Dr Welby, who worked in the oil industry before being ordained, is due to visit the summit on Monday and will meet with groups including young members of the Anglican community and indigenous people.
He warned radical action is needed but said there is still time to “save our world from the worst of the catastrophe”.
We can, and must, choose life, so that our children may live
Justin Welby, Archbishop of Canterbury
He said: “The Cop26 climate talks are emergency surgery for our world and its people.
“The outcome will be life or death for millions of people. That’s how seriously we must take this moment.
“The eyes of the world are on Glasgow: leaders must deliver for the whole human family. We can, and must, choose life, so that our children may live.
“If these talks do not deliver, we face a dark, disturbing future – but there is still time, just, to save our world from the worst of the catastrophe.
“This is a chance to start living in a way that is healthier, kinder, and better for everyone.”
The Church of England has divested from coal companies and says it will pull investment by 2023 from oil and gas firms that are not on a pathway to zero emissions.
It has also led the way on an initiative now supported by investors with funds worth 40 trillion US dollars to assess companies’ climate performance.
Dr Welby said he hopes the plight of communities most affected by climate change will be highlighted at Cop26.
“It is their voices that I hope are heard, along with those of everyone on the burning front lines of climate injustice: the poorest, most vulnerable, and marginalised people already living with droughts, floods and vanishing natural resources,” he said.
“People who face ruined lives and livelihoods, mass migration, instability, famine, war, and death.
“People who see our prosperity, our vaccines against all manner of diseases including Covid-19, and yet do not share in their benefit.
“We can no longer ignore the cries of people who are oppressed and of the groans of our Earth.”