Barry D. Wood

Special for USA TODAY

BRISBANE, Australia — President Obama's climate change agreement with China, which was announced Wednesday, has changed the agenda for the G-20 summit that started Saturday.

The U.S.-China pledge announced in Beijing to reduce carbon emissions caught Australian summit planners off guard. The accord between the world's two biggest polluters had not been expected, and Australia's conservative prime minister Tony Abbott initially resisted putting climate change on the G-20 agenda. Australia is the rotating chairman of the G-20, formed in 2008 to deal with pressing global economic issues.

In Brisbane, Obama will announce a $3 billion U.S. contribution to the United Nations Green Climate Fund that facilitates poorer countries' investments in clean energy. The George W. Bush administration into 2008 had pledged $2 billion to the World Bank's Climate Investment Funds.

U.S. officials say the contribution will promote sustainable growth while preserving stability and security in some of the world's most fragile regions. The contribution, they say, demonstrates the need to reach across traditional divides to tackle climate change.

The G-20 summit brings together heads of state and government from both advanced and emerging economies. Several of the leaders, including Obama and Russian President Vladimir Putin, participated in the Asia Pacific Economic forum in Beijing this week.

The U.S.-China commitment to cut emissions is being praised by European leaders at the summit. EU council President Herman Van Rompuy said Saturday the deal is significant and makes success more likely at next year's climate conference in Paris. Van Rompuy emphasizes that the 28 European Union countries comprise the world's most energy-efficient region, having already cut carbon emissions by 40%.

In the agreement, the United States said it would reduce carbon dioxide emissions between 26% and 28% from 2005 levels by 2025, while China agreed to a peak emissions level by 2030 and then start to reduce.

United Nations Secretary-General Ban Ki Moon called the U.S.-China deal "significant and makes it more likely we shall have a meaningful global agreement on climate by the end of 2015."

Andrew Steer, president of the World Resources Institute, says the actions announced this week "have breathed new life into global climate action." However, congressional Republicans have criticized the deal. Incoming Senate Majority Leader Mitch McConnell called it part of Obama's "ideological war on coal" that will hurt the American middle class, particularly coal miners.

G-20 leaders will discuss climate change Sunday morning. The Ebola epidemic in West Africa is to be discussed informally at the final luncheon before leaders begin returning home Sunday afternoon.

Obama, after more than 10 hours of meetings in Brisbane, will hold a final press conference Sunday afternoon. The president's speech to university students on Saturday focuses on the administration's pivot to Asia, a recurrent theme in the president's travels this past week.

John Kirton, the head of the G-20 Research Center at the University of Toronto, criticized Abbott's failure to include the crisis in Ukraine on the summit agenda. Kirton says Abbott should have allowed the issue to be raised formally, even if Russia and China would have been opposed or refused to participate.

Kirton, who has analyzed both G-7/8 and G-20 summits since 1988, credits Putin, last year's host, for including the sensitive subject of chemical weapons in Syria on the 2013 agenda. There was, says Kirton, agreement on the need to address the problem and the subsequent removal of chemical weapons from the war-torn country "saved thousands of lives."