The panel made its Synthesis Report available now because a new international treaty on climate will be attempted next year. (The report is here and a very short summary is here.) It is a “synthesis” report because it sums up several previous reports, but the language in this new one may be more stark than any of the publications that have come before. Among its warnings: The impact of warming is already being observed around the world. Levels of greenhouse gases in the atmosphere are higher than they have been at any time in 800,000 years. Burning fossil fuels without attempting to limit their carbon impact must end by 2050 or damage to climate will be irreversible.

But the