31 degrees is still freezing

If by global warming YOU mean...

As a kid, winter temps in MN got as low as -15 degrees plus windchill for -20 degrees of brutal unlivable outdoor conditions.

Today...

 Or rather this Friday, the low temp in MN is reported at -11 degrees.

So if by global warming you mean in 30 years the winter temperatures in MN has risen -9 degrees, then yes, global warming.

Freezing temperature is 32 degrees, FYI. Water freezes at 32 degrees.

Therefor...

So do humans.

But like I said before, enjoy your global warming at -11 degrees!