U.S. President Barack Obama will host a summit of world leaders in April to help forge a UN agreement on global warming, the White House said Saturday.

The April 27-28 summit, labelled by the White House as the Major Economies Forum on Energy and Climate, will include 16 major economies.

The White House said in a statement the Washington summit "will facilitate a candid dialogue among key developed and developing countries, [and] help generate the political leadership necessary to achieve a successful outcome at the UN climate change negotiations."

World leaders will meet in Copenhagen in December in an effort to produce a UN treaty on climate change to replace the Kyoto protocol, which expires in 2012.

Canada is among the countries invited to the forum. Environment Minister Jim Prentice has said Canada's environmental policies will mirror those of the Obama administration.

The Conservatives have said they plan to lower greenhouse gases by three per cent from 1990 levels by 2020, or 20 per cent from 2006 levels over that same period.

Obama has established a similar goal of reducing greenhouse gases to 1990 levels by 2020.

The Kyoto protocol, in contrast, sets out an agenda for reducing greenhouse gas emissions by 5.2 per cent from 1990 levels, although "economies in transition," like Russia, can pick different base years. Canada had initially signed on, but the Harper government abandoned its targets in 2006.

Talks to focus on clean energy, emissions

The U.S., which initially signed on to the 1997 Kyoto accord, later backed out under the presidency of George W. Bush. Obama has signalled he is ready for a shift in U.S. environmental policy, prioritizing clean energy and slashing greenhouse gas emissions through a cap-and-trade program.

April's meeting will focus on these two priorities, the White House said.

The announcement came as millions around the world turned off their lights Saturday to mark Earth Hour, and a day before 190 countries are set to meet in Germany to lay some of the groundwork for the Copenhagen summit.

The following countries will be invited to the April forum: Australia, Brazil, Canada, China, the European Union, France, Germany, India, Indonesia, Italy, Japan, Korea, Mexico, Russia, South Africa, the United Kingdom, and the United States.

Denmark, host of December's Copenhagen summit, and the United Nations have also been invited.