Which one of the following provides the cryogenic indicator of climate change?

The answer is A) Ice core. The word "cryogenic" points to the cryosphere, the frozen part of the Earth system, and ice cores are the main archive from it. Air bubbles trapped in ice preserve past atmospheric CO₂ and methane, and oxygen and hydrogen isotope ratios act as paleotemperature proxies. The Vostok (Antarctica) record goes back about 420,000 years, and EPICA Dome C goes back about 800,000 years.

• B) Fossilized pollen is a palynological proxy. It reflects vegetation and terrestrial climate shifts, not the cryosphere.
• C) Tree ring growth is dendroclimatology. It works well for the last few centuries to millennia, but it is not a cryogenic archive.
• D) Evaporite deposits form when water evaporates in arid or saline settings. They indicate dry, hot conditions, not ice.

For Mains, ice cores connect to the retreat of Himalayan glaciers such as Gangotri and to the debate on anthropogenic warming, since they show the current CO₂ rise is unprecedented in the core record.

Trap: Students see "tree" or "pollen" and pick a biological proxy because it looks like a climate record. Ask first which archive belongs to the cryosphere.