Its different. The science behind it is murky imo. Its guesstimation and thats a wild stretch of the word. Just think about it. A chunk of ice telling you the weather millions of years ago? Use your head, be rational. Does that sound like a thing thats real or accurate if it is real?
Lets say I had never seen a plane and though they were impossible. You could show me the parts and show me how it works and how it flys and then I could say ok now I get it. Its in the here and now, I can touch it. Tell me about ice samples showing me the temperature mil of years ago is silly.
Same as those stories of oh theres a sun 50 galaxies away thats exactlly this big and this hot etc. Oh what camera are we using to see this sun so far away when we can barely scrape our own galaxy thats like a grain of sand on a beach?
Whats hard to understand? Heres a quick step by step guide to get you up to speed:
1. In perenially cold regions, ice melts very little, if at all.
2. As a result it accumulates, sometimes in sheets miles thick.
3. When the ice sheets are formed, debris and bubbles of air are trapped.
4. The debris and air pockets are reflective of local geologic and atmospheric conditions when the ice was formed.
5. If the core sample from theses sheets is deep enough, you can effectively estimate conditions from thousands of years ago, when the bottom layers were formed.
6. Plotting things like CO2 content in the trapped bubbles vs. depth (time) leads to predictive models which can extrapolate even more ancient levels of greenhouse gasses.
Its kind of like the rings of a tree indicate age and conditions while it was growing, except the deepest ice cores can provide data from ~ 800,000 years ago.