This image of a freshly-fallen snowflake was captured with Environmental Scanning Electron Microscopy.

As snowflakes form, air is trapped within the lattices of the crystal. If the snow doesn't melt, and instead accumulates and packs down, the structure of the snowflakes changes in all kinds of interesting ways.

By drilling into Arctic & Antarctic glaciers and examining the ice cores brought up, researchers can look at snow that has built up over tens of thousands of years. The air that was trapped can be analyzed to help figure out what the climate was like at the time the snow fell. The evidence is there, regardless of how nasty a few scientists get toward denialists. (Those scientists have since received "torrents" of death threats.)

Here in semi-arid western Kansas, we usually don't have to worry about that much snow. In fact, we're grateful for whatever precipitation we get - except for ice.