President Barack Obama on Friday pledged a $3 billion U.S. contribution to an international fund to help poor countries cope with the effects of climate change, putting the issue front and center of the Group of 20 summit in Australia.

The large size of the contribution — doubling what other countries had previously pledged ahead of a Nov. 20 deadline — took climate policy watchers by surprise. It would be the second major move on climate change taken by Obama after big Democratic losses in the Nov. 4 midterm elections.

"Along with other nations that have pledged support, we'll help vulnerable communities with early warning systems, stronger defenses against storm surges and climate-resilient infrastructure," Obama said in remarks ahead of the official opening of the G-20 summit. "We'll help farmers plant more durable crops. We'll help developing economies reduce their carbon pollution and invest in clean energy."