 Environment ministers lack power to lead a fight against global warming at a time when ever more governments portray climate change as one of the biggest threats to the planet, experts say. Environment ministers are sometimes rising stars -- German Chancellor Angela Merkel had a stint in the 1990s -- but are often far less experienced than cabinet colleagues in charge of issues such as defence, health or education. "I don't think they are too junior to get things done but the portfolio doesn't cover all of the essential issues" such as energy or competition policy, Yvo de Boer, head of the UN Climate Secretariat, told Reuters. He met UN Secretary-General Ban Ki-Moon in New York on Monday to press his call for a summit of about 20 world leaders to spur stalled talks on widening the UN's Kyoto Protocol on curbing global warming beyond a first period ending in 2012. "Heads of state and government...are in a position to say 'this is the direction in which things should go'," he said. More and more government leaders are making apocalyptic warnings about climate change. Many scientists say a build-up of greenhouse gases from burning fossil fuels will bring more floods, heatwaves, desertification and raise world sea levels. "The excessive exploitation of natural resources is upsetting the climate and will endanger mankind, if we don't react right now," French President Jacques Chirac, for instance, said in a New Year address. "In many countries the environment minister doesn't have the bureaucratic tools or power," said Paal Prestrud, head of the Centre for International Climate and Environmental Research, Oslo. "Either the prime minister or the minister of finance has to take on the role or you strengthen the environment ministry." One UN official noted the Kyoto Protocol, binding 35 nations to cut emissions of greenhouse gases, seeks to promote investments in clean energies such as wind or solar power in poor nations -- and development ministers often have more access to funds than environment ministers. Still, in a sign that the environment may be becoming more of an issue with voters, Canada's Conservative Prime Minister Stephen Harper made sweeping changes to his cabinet on January 4 largely to bolster a fight against climate change. Harper picked John Baird to take over from Environment Minister Rona Ambrose, widely criticized for doing too little to rein in greenhouse gas emissions. Harper praised Ambrose but said: "We recognise that, particularly when it comes to clean air and climate change, that Canadians expect a lot more." President George W Bush pulled the United States out of Kyoto in 2001, saying the plan would cost too much and wrongly excluded developing nations such as China and India. Unlike most nations, Washington does not have an environment minister. Stephen Johnson heads the Environmental Protection Agency while Paula Dobriansky, Under Secretary of State for Democracy and Global Affairs, heads the US delegation at UN talks.