The formal notification by the United States that it will leave the 2015 Paris climate change agreement — two years after President Donald Trump announced his administration's intention to do so — comes amid fresh reminders of the serious effects of global warming in the form of more frequent extreme weather conditions accompanied by more devastating damage.

The exit of the world's second-largest emitter of greenhouse gases marks a setback for the framework accord just before its measures to fight global warming start to kick in next year. Key participants in the Paris accord, including Japan, need to make extra efforts to shore up the agreement by upgrading their commitment to reduce their own emissions of heat-trapping gases. Merely calling the Trump administration's decision "regrettable" is not enough.

To avert the catastrophic effects of climate change, the Paris agreement sets a target of keeping the rise in global temperature well within 2 degrees Celsius from pre-industrial levels and close to 1.5 degrees. What's clear is that the voluntary pollution-reduction targets set so far by the participating countries, even if achieved, would be far from sufficient to tame climate change. Therefore, the signatories must keep upgrading and meeting their commitments.