Comparatifs et superlatifs en anglais

Transform the adjectives in brackets to complete the sentences correctly. Pay attention to the rules for short ($1$ syllable) vs long ($2+$ syllables) adjectives, and the special cases for superlatives.

1. The Sahara Desert is (dry) __________ desert in the world.
2. The Amazon rainforest is (big) __________ than any other forest on Earth, covering an area of approximately $5,500,000$ $km^2$.
3. Mount Everest is (high) __________ than K2, making it (dangerous) __________ mountain to climb for inexperienced hikers.
4. Many scientists believe that the impact of climate change is (bad) __________ now than it was $20$ years ago.