De or het warming?

The correct Dutch article is:

de warming

Rule Words ending in -ing: almost always de. See the rule
Meaning (Dutch) het warmen

How to use warming

the warmingde warming
this warmingdeze warming
that warmingdie warming
our warmingonze warming
your warmingjouw warming
every warmingelke warming
which warming?welke warming?
a big warming / the big warmingeen grote warming, de grote warming

Dutch words ending in warming

housewarming | opwarming | klimaatopwarming | verwarming | wijkverwarming | blokverwarming | autoverwarming | vloerverwarming | stadsverwarming | heteluchtverwarming | achterruitverwarming | huiswarming

In compound words, the last part decides the article. See the rule

Dutch words starting with warming

warming-up

Meaning, plural, diminutive, pronunciation and translations: WikiWoordenboek (Dutch Wiktionary) (CC BY-SA 4.0). Example sentences: Tatoeba (CC BY 2.0 FR).