What's the exact meaning "for much more of the 21st" indicate?
The speaker is talking about the way we humans consume meat is unsustainable.

"The way we eat meat will go down as a historical anomaly,
one that began in the mid-20th century, and can't continue **for much more of the 21st.**"
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I'm not sure about the exact meaning of the part marked in stars.
Does it mean the same as just "much of 21st"? Or is it "the rest of the 21st" we have?
What does the sentence mean exactly and what's the key element to understand it? it it "more"?

Question

What's the exact meaning "for much more of the 21st" indicate?
The speaker is talking about the way we humans consume meat is unsustainable.
﻿
"The way we eat meat will go down as a historical anomaly,
one that began in the mid-20th century, and can't continue **for much more of the 21st.**"
-

I'm not sure about the exact meaning of the part marked in stars.
Does it mean the same as just "much of 21st"? Or is it "the rest of the 21st" we have?
What does the sentence mean exactly and what's the key element to understand it? it it "more"?

Answer

It means that it will have to change soon. The word 'more' refers to the proportion of the remaining 80 years of this century.

It's now nearly 2020. We have already been consuming meat in an unsustainable way for the first twenty years of this century. We can't continue 'for much more of the 21st' [century] means that we cannot go on like this 'for many more years of this century'. For example, we can't go on cutting down forests for cattle grazing at this rate until for example, the 2070s or the 2080s.  We need to change these practices before then - say, by 2030.

Answer

So it implies that it can't sustain for more than 21st? the way we eat meat is going to be different in the 22st?

Answer

It means that we ate a lot of meat during a part of the 21th century, but can't go on for long before we have to stop