Learn Italian: È probabile che le emissioni globali diminuiranno. - It is probable that global emissions will decrease.

You are right that è probabile che normally triggers the subjunctive. However, because the decrease will happen in the future, we use the future indicative. Italian doesn't have a future subjunctive tense, so whenever a dependent clause needs to show an action happening later than the main clause, the regular future tense steps in.

How do I know the gender of emissioni?

The singular noun is emissione. As a very reliable rule, Italian nouns ending in -sione or -zione are feminine. Since it is plural here, it takes the feminine plural article le.

Why does the adjective globali end in -i if the noun is feminine?

The singular form of this adjective is globale. Adjectives that end in -e in the singular do not have separate masculine and feminine forms; they simply change to -i in the plural for both genders.

How is the future tense formed for diminuire?

Diminuire is a regular -ire verb. To form the future tense, you drop the final -e from the infinitive and add the standard future endings. For the they form (loro), the ending is -anno, giving us diminuiranno.