JOHANNESBURG: Greenpeace will keep up the pressure on leaders it believes let the world down on global warming, the head of the international environmental group said.

Kumi Naidoo, Greenpeace's executive director, spoke Thursday in Johannesburg on a visit to his home country after last week's U.N. climate change summit in Copenhagen. Back in Copenhagen, four Greenpeace activists will spend Christmas in a Danish jail facing trespassing charges because of a summit protest.

Greenpeace had pushed for a legally binding agreement to reduce global warming and give poor countries money and technology to cope with climate change. The Copenhagen talks fell short of those ambitions, producing a nonbinding political agreement that has been denounced even by some of its key drafters.

Naidoo said the flurry of criticism since the talks concluded over the weekend ``is going to put more pressure on leaders.

``One thing our political leaders have learned is that they have to up their game,'' he said. ``We hope they've learned that they have to come, in the month to follow, with more specific commitments and that they have to do more political work back home.''

He said citizens and groups like his have to ensure leaders don't delay action and opportunities to continue negotiating until the next round of talks next year in Mexico City. Already, he said, too much time has been lost.

``Given that time is running out, I think that people have a right to feel extremely let down by their political leaders,'' he said.

But he said Copenhagen did produce consensus that can be built on, including broad agreement that developing countries that have not contributed to global warming and are likely to be hardest-hit by climate change need help to cope. The Copenhagen meeting, he said, also saw political acknowledgment of what science says about climate change.

``Bottom line is, not one head of state got up and said: `I question the science,''' Naidoo said.

Naidoo said a Greenpeace climate-change team that worked for the 18 months before Copenhagen has been replaced with fresh campaigners, ``so we won't lose momentum.'' But he said the jailing of the four activists from the Netherlands, Norway, Spain and Switzerland has been a distraction.

Three have been jailed awaiting charges since crashing a Dec. 17 banquet Danish Queen Margrethe II hosted at the Danish parliament for heads of state attending the climate conference. The protesters unfurled a banner reading: ``Politicians talk, leaders act.'' The fourth was arrested the following day, accused of helping plan the protest.

Naidoo said it was a Greenpeace tradition to appear at trials stemming from such a protest, in part as an opportunity to publicly explain the group's motives. He said there was no reason not to grant the four bail, particularly so close to the holidays.

But, he said, Danish authorities appeared to be taking a hard line because of embarrassment over the security breach. The protesters' limousine, fitted with a fake police light, joined a convoy of vehicles, including one carrying US Secretary of State Hillary Rodham Clinton, on the way to the dinner.

Bail applications were rejected Wednesday, with the four ordered held until a Jan. 7 hearing at which they expected to be charged with trespassing, falsifying a license plate and impersonating a police office, Naidoo said.

``To deny folks bail to be home with their families over Christmas and New Year's ... seems unnecessarily inhumane and cruel behavior on the part of the Danish authorities,'' Naidoo said, adding he would return to Copenhagen for the January hearing.

Danish police did not return calls seeking comment on the case