as the planet moves toward another ice age.

[keannu]

In "as the planet moves toward another ice age.", does "as" mean "because" or "when" or "while"?
Considering the whole context, I think it's "because", but I'm not sure as the following reasons seem to say earth's moving is not happening at the moment. I know I have to judge the meaning of "as" depending on context, but it's always hard.

go2mo1-44
ex) In ages past, the Earth passed through a series of ice ages,in which much of the Northern Hemisphere was covered with glaciers. The mild temperatures we’re familiar with occur between ice ages. It is thought that very slight changes in the position of the Earth relative to the sun are behind these shifts in climate. Scientists say that we can expect colder temperatures as the planet moves toward another ice age. But don’t build your igloo yet.
Not only is the next ice age still thousands of years away, it’s possible that it might not arrive at all. Global warming, caused by an increase in carbon dioxide and other gases in the atmosphere, may prevent the next ice age from occurring.

 

[emsr2d2]

In "as the planet moves toward another ice age.", does "as" mean "because" or "when" or "while"?
Considering the whole context, I think it's "because", but I'm not sure as the following reasons seem to say earth's moving is not happening at the moment. I know I have to judge the meaning of "as" depending on context, but it's always hard.

go2mo1-44
ex) In ages past, the Earth passed through a series of ice ages,in which much of the Northern Hemisphere was covered with glaciers. The mild temperatures we’re familiar with occur between ice ages. It is thought that very slight changes in the position of the Earth relative to the sun are behind these shifts in climate. Scientists say that we can expect colder temperatures as the planet moves toward another ice age. But don’t build your igloo yet.
Not only is the next ice age still thousands of years away, it’s possible that it might not arrive at all. Global warming, caused by an increase in carbon dioxide and other gases in the atmosphere, may prevent the next ice age from occurring.

Here, it's "while".

Over/During the period of time that the planet is moving towards the next ice age, temperatures will get lower.

 

[keannu]

Thanks a lot! And does it mean a general phoenomeon that might or might not happen or the planet's moving actually?

And this might be a simple question. I thought "while" for "as" is when two actions happen simultaneously, but "when" for "as" is kind of vague, not that distinguished from "while" for "as", for exmple, the following "as" is interpreted as "when", but how is it different from "while"?
ex)As I got on the bus, I felt really tired from the day's work.

 

[SoothingDave]

And does it mean a general phoenomeon that might or might not happen or the planet's moving actually?​

That answer is more a political one than one of language. It certainly seems that the author of this text believes that the planet is moving towards a new ice age. Unless "global warming" prevents it.