It's freezing cold. The ending -AS always shows that something is happening right now. Technically, this is called the present tense of the verb. Roots and Words English is based around words. Most Esperanto words are based around on an even shorter unit, the root.
Roots are basic units of meaning in Esperanto.
The meanings contained in roots can refer to objects, actions, or attributes. In Esperanto, we show the use of a word in a sentence with a grammatical ending. By changing the endings we change the word's use without changing the root's inherent meaning. The second shortest type of sentence is the one that shows something doing something, or something happening to something. The name of the thing doing something or having something happen to it is the subject.