من المتوقع أن تكون الانبعاثات الكربونية منخفضة.

من المتوقع is a very common fixed expression meaning it is expected.

Literally, من usually means from or of, but in this expression you should not translate it word-for-word. The whole phrase functions idiomatically. A useful way to learn it is simply as a chunk:

• من المتوقع أن... = it is expected that...

Also, المتوقع is the passive participle of توقّع (to expect), so the sense is the expected or what is expected.

Arabic often does not use a dummy subject like English it.

So instead of saying something like it is expected that..., Arabic can simply say:

• من المتوقع أن...

This is normal and natural. The same thing happens in other expressions too:

• من الممكن أن... = it is possible that...
• من الواضح أن... = it is clear that...

So the sentence is not missing anything; Arabic just structures the idea differently.

Here أن introduces a subordinate clause, roughly like English that in it is expected that...

After أن, Arabic normally uses a present-tense verb in the subjunctive. That is why the next word is تكون.

So the structure is:

• من المتوقع = it is expected
• أن تكون... = that ... be / that ... will be / that ... are

The exact English translation depends on context, but grammatically أن is the particle that opens the clause.

That is a very common and very good question.

In a simple present-tense nominal sentence, Arabic usually does omit is/are:

• الانبعاثات الكربونية منخفضة = The carbon emissions are low

But after أن, Arabic typically wants a verb, so تكون is used to carry the meaning of be:

• أن تكون الانبعاثات الكربونية منخفضة = that the carbon emissions be / are low

So yes, Arabic often omits is/are in simple present statements, but in this pattern أن + verb, the verb تكون is needed.

Because its subject is الانبعاثات, and انبعاثات is a non-human plural noun.

In Modern Standard Arabic, non-human plurals are very often treated grammatically as feminine singular for agreement. So Arabic uses:

• تكون not يكون
• منخفضة not منخفضون or منخفضات

This is a very important pattern to get used to. Even though الانبعاثات means emissions and is plural in meaning, the grammar often treats it like a feminine singular for agreement purposes.

For the same reason: الانبعاثات is a non-human plural, and in MSA non-human plurals usually take feminine singular agreement. This is often called deflected agreement.

So:

• الانبعاثات الكربونية = literally plural in meaning, but the adjective الكربونية is feminine singular in form
• الانبعاثات ... منخفضة = the predicate adjective منخفضة is also feminine singular

This pattern is extremely common:

• الكتب الجديدة = the new books
• السيارات سريعة = the cars are fast

So the agreement in your sentence is completely normal.

Because the two words are doing different jobs.

الكربونية is an adjective directly describing the noun الانبعاثات inside the noun phrase:

• الانبعاثات الكربونية = the carbon emissions

Since الانبعاثات is definite with الـ, the adjective الكربونية must also be definite.

But منخفضة is not part of that noun phrase. It is the predicate of تكون:

• تكون الانبعاثات الكربونية منخفضة = the carbon emissions are low

Predicate adjectives are normally indefinite, so منخفضة does not take الـ.

A useful contrast:

• الانبعاثات الكربونية المنخفضة = the low carbon emissions
  Here المنخفضة is an adjective inside the noun phrase.
• الانبعاثات الكربونية منخفضة = the carbon emissions are low
  Here منخفضة is the predicate.

In your sentence, الكربونية is an adjective meaning carbon / carbon-related.

So:

• الانبعاثات الكربونية = the carbon emissions

Yes, Arabic can also express this idea with an iḍāfa construction:

• انبعاثات الكربون = carbon emissions or more literally emissions of carbon

Both are understandable. The sentence you were given uses the adjectival form الكربونية. In real-world environmental Arabic, انبعاثات الكربون is also very common.

The singular is انبعاث = emission.

The plural is انبعاثات = emissions.

This is a common plural type ending in ـات. Even though it has that ending, it is still a non-human plural, so it follows the agreement pattern discussed above: feminine singular agreement in many contexts.

A fully vowelled version is:

مِنَ المُتَوَقَّعِ أَنْ تَكُونَ الِانْبِعَاثَاتُ الكَرْبُونِيَّةُ مُنْخَفِضَةً

The main grammar points are:

• المتوقعِ is genitive because it comes after من
• تكونَ is in the subjunctive after أن
• الانبعاثاتُ is the subject of تكون, so it is nominative
• الكربونيةُ matches الانبعاثات as its adjective, so it is also nominative
• منخفضةً is the predicate of تكون, so it is accusative

In normal everyday writing, these short vowels are usually omitted.

Yes. Some natural alternatives are:

• يُتَوَقَّعُ أن تكون الانبعاثات الكربونية منخفضةً
  = It is expected that the carbon emissions will be low

• من المتوقع انخفاضُ الانبعاثات الكربونية
  = A decrease in carbon emissions is expected

• من المرجّح أن تكون الانبعاثات الكربونية منخفضةً
  = It is likely that the carbon emissions will be low

These are all slightly different in style, but the original sentence is perfectly natural and clear.