An international team of scientists last week issued a stark warning: the early effects of global warming are upon us, and letting greenhouse gas emissions continue unabated could take us past a tipping point where catastrophic changes become irreversible.

Some may take that grim forecast as an invitation to inaction. But the same scientists who say we are nearing a dangerous threshold also say we can avoid the most dangerous consequences of climate change if we act quickly to cut carbon pollution.

How much? About two percent a year. If we start now, we can put the U.S. on a path to reducing our emissions by 80 percent from current levels by 2050 – enough to help avoid the worst impacts predicted by the Intergovernmental Panel on Climate Change. If we wait, the cuts will have to be deeper, the costs will be higher, and our chances of success smaller.

The next report from the IPCC will offer some suggestions for how to get started.  That will add to the growing Congressional debate over how to move forward on low-carbon energy sources and technologies for capturing emissions before they are released into the atmosphere.

One thing is certain. Only a firm cap on carbon dioxide emissions can guarantee the reductions the science says we need and spur the development of technologies that will ensure our success in the long term.