U.N. Secretary-General Kofi Annan has opened high-level talks at the U.N. Climate Change conference in Kenya, by urging leaders and their governments to get serious about tackling what he calls the "all-encompassing threat."

In his opening address, Annan said that there is a "frightening lack of leadership" with respect to countries curbing their carbon dioxide and other emissions linked to climate change.

Speaking later to reporters, Annan said governments and the people who elect them need to take more responsibility for reigning in climate change.

"I think there are many leaders who are not taking climate change seriously, and I would want leaders around the world to really show courage and to know that if they do, their people and the population and the voters will be with them,? he said.  ?If they do not, I think the population and the voters should take the lead to let them know that they consider climate change seriously and that there may be a political cost if they don't show the political leadership to move the process forward."

Annan said the Kyoto Protocol is a solid first step, but additional measures by governments, business, consumers and others to curb harmful emissions must be implemented.

The 165 countries that ratified the Kyoto Protocol, which took effect last year, are legally committed to reducing their output of six carbon gases most responsible for causing global warming.

The worst of these gases is carbon dioxide, the by-product of burning oil, gas, and coal.  In industrialized countries, a lot of this burning gas and oil comes from car emissions.

Others include methane and nitrous oxide.  The gases form a barrier that prevents the sun's energy from radiating back into space, thus raising the earth's temperature.

Such climate change has been linked to more frequent occurrences of drought, flooding, hurricanes, forest fires, and increases in the number of malaria cases, with long-term impacts being rising sea levels and damage to crops.

The United States and Australia have refused to ratify the protocol, raising the ire of many experts and activists.  The United States accounts for about one quarter of the world's greenhouse gas emissions.

Annan urged the holdout countries to cut down on their emissions.

?If they do not sign the Kyoto agreement, they have to act, and be in step with the rest of the world or the rest of the industrialized world,? he added.  ?They have a responsibility to their citizens and to the rest of the world and the people who we share the planet with to bring their emissions under control.  Some American leaders have told me, 'We have not signed Kyoto, but we are going to take measures to fulfill it or even go beyond.'  So, let us wait and see if that happens."

The United States says the Kyoto treaty does not place enough responsibility on developing countries to cut pollution and its costs would harm the U.S. economy.

The U.N. Climate Change conference ends Friday.