Promising move on climate change but what will Republicans say now?

Now that China has committed to producing enough zero-emissions energy by 2030 to power the entire United States, Sen. Mitch McConnell and his fellow Republicans will have to find a new excuse for doing nothing about climate change.

McConnell has demurred on the link between carbon emissions and a warming planet, saying he's "not a scientist."

But the Senate's soon-to-be majority leader has been emphatic that U.S. efforts to reduce greenhouse gases would be pointless without a similar effort by China, the world's largest source of such emissions, ahead of only the United States.

Well, China has made that commitment.

The agreement to lower carbon output announced Tuesday by presidents Xi Jinping and Barack Obama at the end of a Beijing summit came as a surprise.

But it's hardly surprising that China is willing, even eager, to reduce its dependence on fossil fuels. China is choking on its coal-fired prosperity as air pollution routinely reaches intolerable levels in many places.

Longer term, it also makes sense that the world's largest country wants to avert massive droughts, floods, rising sea levels, superstorms and the resulting conflicts, suffering, chaos and costs.

If anything is shocking, it's the lack of urgency in the U.S. Congress, especially among Republicans, to protect our descendants from climate disaster.

The goals on which Obama and Xi agreed are a long way from realization and will require work, investment and vigilance on both ends.

Even if both countries succeed in their commitments, experts say that alone would not avert a 2 degrees Celsius (3.7 degrees Fahrenheit) increase in average temperatures. That's the threshold at which scientists say the worst effects of climate disruption become unavoidable. Developing countries, especially India, must also begin unlinking their economies from fossil fuels, and Europe must keep up its momentum toward clean energy.

This agreement, nonetheless, is being hailed as a huge encouraging step and a new way forward.

Republicans and coal-state Democrats will grouse that Obama and the Environmental Protection Agency are abusing their authority by ordering further cuts in emissions from coal-fired power plants. The EPA also is moving to limit methane emissions from natural gas production and to require cleaner vehicles.

The president should keep telling himself that it's better to suffer the political attacks now than the harsh judgment history will render if he puts less than all his power into solving this most pressing challenge to humankind's future.