Every December, more than 25,000 scientists from around the globe descend upon a cavernous convention center to eat dry sandwiches, drink weak coffee and ponder all things Earth and climate and space.

This is the annual meeting of the American Geophysical Union, a nonprofit organization for scientists, and it is the place to be if you want to hear about the latest research on topics like melting ice caps, prehistoric droughts and the long-term environmental effects of U.S. bombing in Vietnam and Laos, as seen from declassified spy satellite imagery. It’s where new discoveries get a first airing and fledging ideas get hammered into shape.

Trying to summarize such a varied gathering would be a fool’s errand. Instead, here are three things I’ve been struck by this week at the conference, which runs through Friday in Washington.

1. Why has the Earth been so much hotter than expected?

Every month for the past year and a half, the planet has been at or near its warmest point in modern times. This year is “virtually certain” to end up as the hottest on record, according to the European climate monitor. Temperature records aren’t being broken; they’re being leapfrogged. And scientists haven’t quite pinned down why.

On Tuesday at the conference, people packed a room to hear seven researchers from three continents share their latest thoughts and findings. By the end, the only thing everyone could agree upon was there was still more work to do.

This month, scientists in Germany put forth a troubling new explanation for the heat: Cloud cover last year was at a record low. In other words, Earth absorbed extra energy because fewer clouds reflected it back to space.