When I reached Heidi Cullen, chief climatologist for Climate Central, she remarked on the glorious weather we were enjoying. But underneath our pleasure at the sunshine and blossoms, we were both feeling uneasy about the warmth. So far all 11 years of the 21st century have been among the 13 warmest years on record, according to the National Oceanic and Atmospheric Administration.

Cullen is in the habit of keeping a close eye on the weather: Climate Central is a nonprofit science research organization headquartered in Princeton, N.J. Before she joined them, Cullen, who holds a doctorate from Columbia University, was the Weather Channel’s first on-air climate expert.