Temperatures in parts of the San Francisco Bay Area were expected to drop into the upper 20s to the middle 30s for the second morning in a row Tuesday, triggering a Freeze Warning and Frost Advisory.

The eventual U.S. departure further threatens the central goal of the agreement to avoid a rise in global temperatures of 1.5 degrees Celsius, a target that appears even more tenuous as last year was the planet's hottest on record.