--- title: "Palaeoclimate: Ice Cores, Isotopes and the Record of Past Change" description: "Past climate is reconstructed from proxies, each of which records something related to temperature rather than temperature itself. Ice cores are the strongest case because they trap the air of the tim" canonical: https://lightmysky.com/learn/science/palaeoclimate-ice-cores-isotopes-and-the-record-of-past-change-mt_JabMZ5ZeaL source: https://lightmysky.com/learn/science/palaeoclimate-ice-cores-isotopes-and-the-record-of-past-change-mt_JabMZ5ZeaL.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Palaeoclimate: Ice Cores, Isotopes and the Record of Past Change Past climate is reconstructed from proxies, each of which records something related to temperature rather than temperature itself. Ice cores are the strongest case because they trap the air of the time alongside an isotope thermometer, letting greenhouse gas and temperature be compared directly. Subject: Science · Area: Earth's Systems · Ages 17 to 18 Page: https://lightmysky.com/learn/science/palaeoclimate-ice-cores-isotopes-and-the-record-of-past-change-mt_JabMZ5ZeaL ## Ready when they can - Explain what an oxygen isotope ratio in ice or in a shell records, and what assumption the reading rests on - Say why trapped air bubbles make an ice core a stronger record than most proxies - Read a palaeoclimate series and distinguish an orbital pacing from an amplifying response ## Lesson: Reading climates without thermometers Nobody measured the air a hundred thousand years ago, so scientists read natural archives instead: ice cores, deep-sea sediment cores, and old shells. Each proxy records something that moved with temperature rather than temperature itself. The honest habit is to measure the proxy, state the assumption linking it to temperature, and only then tell the climate story. The busiest thermometer is the oxygen isotope ratio. Water comes in slightly different weights, and the balance of heavy and light oxygen trapped in ice or shells shifts with the conditions of formation. In shells it records how much of Earth's water was locked into ice sheets when the shell grew. Plotted down a core, the values swing with a rhythm matching slow wobbles in Earth's orbit. Ice cores add a second gift: tiny air bubbles sealing actual samples of the ancient atmosphere. That makes an ice core stronger than most proxies, because greenhouse gas and temperature can be compared directly in the same layers. Gas on one side, isotope thermometer on the other, both read from one archive. **Example.** Take one ocean core and split the signal in two. The orbital wobbles set the pace of the ice ages, while ice reflectivity and greenhouse gases amplify each nudge into a full freeze or thaw. Deep freezes like Snowball Earth and hothouse spikes like the PETM show the same old coupling of carbon and temperature at work. **Recap.** Proxies plus stated assumptions rebuild past temperature, and bubbles add ancient air. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Sediment on the Move: Rivers, Coasts and Where It Settles](https://lightmysky.com/learn/science/sediment-on-the-move-rivers-coasts-and-where-it-settles-mt_d1vVJBG6K7) - [Isotopes and Relative Atomic Mass](https://lightmysky.com/learn/science/isotopes-and-relative-atomic-mass-mt_NFoRZd6UN_) - [Reading Ancient Climate Records](https://lightmysky.com/learn/science/reading-ancient-climate-records-mt_olFzbawexJ) - [Forcing, Feedback and Climate Sensitivity](https://lightmysky.com/learn/science/forcing-feedback-and-climate-sensitivity-mt_os28W6fEkW) ## Opens up - [The Carbon Cycle on Two Timescales](https://lightmysky.com/learn/science/the-carbon-cycle-on-two-timescales-mt_OXBubQOPk7)