The Queen urged 53 Commonwealth countries gathered for a summit in Trinidad to forge a common stand on fighting climate change ahead of a world gathering on the matter next month.
Her comments came as key players from outside the Commonwealth membership showed up at this Port of Spain meeting to press for momentum on tackling global warming in the lead-up to a global summit in Copenhagen next month.
Those attending the Commonwealth summit to push for consensus on climate change include UN chief Ban Ki-moon, French President Nicolas Sarkozy and Danish Prime Minister Lars Loekke Rasmussen.
The Queen warned Commonwealth leaders they must act in order to avoid climate change that will affect the world's poorest.
"On this, the eve of the UN Copenhagen summit on climate change, the Commonwealth has an opportunity to lead once more," the monarch said.
"The threat to our environment is not a new concern. But it is now a global challenge which will continue to affect the security and stability of millions for years to come."
"Many of those affected are among the most vulnerable. And many of the people least well able to withstand the adverse effects of climate change live in the Commonwealth."