Learn Hardcore Spanish (Spain): El cambio climático debe de afectar ya a este valle, porque nieva menos cada invierno. - Climate change must already be affecting this valley, because it snows less every winter.

deber + infinitive → obligation / duty
- El cambio climático debe afectar a este valle.
  = Climate change ought to / must (is obliged to) affect this valley.
deber de + infinitive → probability / supposition
- El cambio climático debe de afectar ya a este valle.
  = Climate change must (probably) already be affecting this valley.

So here the speaker is not saying “it is obliged to affect it”, but “I conclude / I suspect it is affecting it.”

In real-life speech, many people drop the de even when they mean probability, but the de is still recommended when you want to clearly mark that it’s a guess, not an obligation.

What does ya add here, and could you leave it out?

ya here means “already / by now / at this point”, and it adds the idea that this is no longer just a future possibility: it has likely started.

Debe de afectar ya a este valle
= It must already be affecting this valley (by now).

If you say:

El cambio climático debe de afectar a este valle.

…it still expresses probability, but without that nuance of “by now / at this stage.” Grammatically it’s fine, but it sounds a bit less urgent, less “it’s happening now.”

Why is it afectar a este valle? In English we just say “affect this valley” without a preposition.

In Spanish, afectar is a transitive verb and normally takes a direct object, but it very often appears with a:

afectar algo or afectar a algo/alguien

With afectar, using a before the object (even when it is not a person) is very common and fully correct:

El ruido afecta a los vecinos.
El cambio climático afecta (a) este valle.

Here, a este valle is functioning as the direct object with a preposition a, which is part of how this verb typically behaves. You cannot calque the English structure directly; in Spanish, afectar a is the natural collocation.

Why a este valle and not en este valle?

afectar a este valle = to affect this valley (the valley is what suffers the effect).
en este valle = in this valley (just locates something inside the valley).

Compare:

El cambio climático debe de afectar ya a este valle.
→ The valley itself is being affected.
El clima está cambiando en este valle.
→ The change is happening in the valley (just a location, not an object of the verb).

So a here marks the valley as the thing being affected, not just the place where something happens.

Why is it just nieva with no subject, instead of él nieva or something like that?

Spanish weather verbs are usually impersonal: they normally appear only in 3rd person singular with no explicit subject. Common ones:

llover → llueve (it rains)
nevar → nieva (it snows)
tronar → truena (it thunders)

You do not say él nieva for the weather. There is no “it” word; the verb alone is enough.

So:

nieva menos cada invierno
= It snows less every winter.

This is the standard, natural way to talk about snow in Spanish.

Why is the present tense used (debe de afectar, nieva) if we’re talking about a trend over time?

Spanish uses the simple present for:

General truths
Habits and repeated events
Ongoing states and long-term processes

So:

Nieva menos cada invierno.
= Every winter, as a habit/trend, it snows less.
Debe de afectar ya a este valle.
= It is probably already affecting this valley (a current, ongoing situation).

You could use other tenses for different nuances (está afectando, ha empezado a afectar, etc.), but the simple present is the default for describing a general tendency or a state you see as true now.

Why is it El cambio climático with el, when in English we just say “climate change” without “the”?

Spanish often uses a definite article where English uses no article, especially with abstract, generic, or well-known concepts:

El amor es importante. → Love is important.
La tecnología avanza rápido. → Technology is advancing quickly.

Similarly:

El cambio climático debe de afectar ya a este valle.
→ Climate change must already be affecting this valley.

You could occasionally see cambio climático without el in titles or more technical contexts, but in normal sentences, el is the most natural choice.

What’s the difference between porque here and por qué with an accent?

porque (one word, no accent) = because (a conjunction that introduces a reason)
- …porque nieva menos cada invierno.
  = …because it snows less every winter.
por qué (two words, with accent on qué) = why (used in direct or indirect questions)
- ¿Por qué nieva menos cada invierno?
  = Why does it snow less every winter?

So in your sentence, you are giving a reason, not asking a question, so it must be porque.

Can you move the porque part to the beginning, like in English “Because it snows less…”?

Yes, you can. Both orders are correct:

El cambio climático debe de afectar ya a este valle, porque nieva menos cada invierno.
Porque nieva menos cada invierno, el cambio climático debe de afectar ya a este valle.

The version with porque at the end is more common and sounds more neutral. Starting with Porque… gives a slightly more rhetorical or emphatic feel, but it’s still natural.

Could you say ya debe de afectar instead of debe de afectar ya? Is there a difference?

Both are grammatical:

Ya debe de afectar a este valle.
Debe de afectar ya a este valle.

The meaning is essentially the same: It must already be affecting this valley.

Nuance:

Ya debe de afectar… puts ya earlier, so it slightly emphasizes the idea of “already, by now” from the very start.
Debe de afectar ya… sounds a bit more neutral; ya comes as a reinforcement at the end of the phrase.

In everyday speech, both word orders are very common.

What’s the difference between cada invierno and todos los inviernos?

Both can translate as “every winter”, and both are acceptable here:

Nieva menos cada invierno.
Nieva menos todos los inviernos.

Nuances are small:

cada invierno treats each winter as one in a series: each winter, individually.
todos los inviernos emphasizes the whole set: all winters (without exception).

In this sentence, cada invierno sounds very natural and is slightly more concise, which is why it’s a typical choice.