Brian Mulroney was honoured Thursday night as the greenest prime minister in Canadian history.

The Canada-U.S. acid rain treaty is probably the best remembered element of Mulroney's environmental record. But he also introduced an ambitious environmental agenda, created eight new national parks and brought in the Environmental Protection Act.

Even some of the former prime minister's fiercest critics showed up at Thursday's ceremony in Ottawa.

Former Liberal environment minister Sheila Copps shared the head table with Mulroney, who was crowned the greenest PM in a survey by Corporate Knights magazine of high-profile environmentalists and others.

When he left office in 1993, Mulroney boasted about his environmental record, and it was only the environmental award that coaxed him to return to Ottawa for the first time in many years.

Wants U.S. at the climate-talk table

In his speech, Mulroney said climate change is the most serious environmental challenge and time is running out.

"Whether the process proves to be Kyoto or something else, let's acknowledge the urgency of global warming and then let's work together to get the United States of America to the table," he said. "It isn't by lecturing the Americans on their record on emissions reduction that we will succeed, especially when our own record is nearly twice as bad as theirs."

On Thursday, the current prime minister reiterated that Canada won't meet the Kyoto targets agreed to by the previous Liberal government.

Stephen Harper brushed aside questions about why the environment isn't one of his government's top five priorities.

Harper, who does not support Kyoto and has not laid out an alternative to it, said his government will make progress over time, something that hasn't happened in a decade.

"He [Mulroney] didn't produce grandiose schemes and unworkable arrangements and the kind of problems we got into with Kyoto," said Harper. "Instead, he decided to make concrete progress, real progress on real issues."

How Harper will proceed in light of Canada's international commitment to the Kyoto protocol remains unclear.