Paleoclimatology
The study of climates of the geological and historical past, reconstructed from natural archives to reveal how and why climate has changed before instruments existed.
Definition
Paleoclimatology is the scientific study of past climates and their causes, using natural recorders of climate, called proxies, to reconstruct conditions from times before instrumental measurements.
Scope
This area covers the reconstruction and interpretation of past climate, from the deep geological past through the ice ages to the last millennium. It treats the natural archives and proxies, such as ice cores, marine and lake sediments, tree rings, corals, and speleothems, that record past conditions; the orbital pacing of the glacial cycles; abrupt climate transitions; and how paleoclimate evidence constrains climate sensitivity and places present-day change in long-term context.
Sub-topics
Core questions
- How can past climate be reconstructed from natural archives?
- What paced the recurring ice ages?
- How abruptly has climate changed in the past?
- What does the deep past reveal about climate sensitivity and the present?
Key theories
- Proxy-based reconstruction
- Physical, chemical, and biological properties of natural archives respond to climate in calibrated ways, so measuring them allows quantitative reconstruction of past temperature, precipitation, and atmospheric composition.
- Orbital pacing of ice ages
- Slow changes in Earth's orbit alter the seasonal and latitudinal distribution of sunlight, pacing the growth and decay of ice sheets over tens of thousands of years.
Mechanisms
Natural archives accumulate layer by layer, locking in chemical and biological signals, such as isotope ratios, trapped gases, growth-band widths, and microfossil assemblages, that vary with climate. By dating these archives and calibrating the proxies against modern observations, paleoclimatologists reconstruct past temperature, ice volume, and greenhouse gas concentrations, and they relate the changes to orbital forcing, volcanic and solar variations, and internal feedbacks.
Clinical relevance
Paleoclimate records reveal the full range of natural climate variability, provide independent constraints on climate sensitivity, and show that present-day greenhouse concentrations and rates of change are unusual in the context of the recent geological past.
Evidence & guidelines
The IPCC Sixth Assessment Report draws on paleoclimate evidence to bound climate sensitivity, to show that recent global temperatures and carbon dioxide levels are exceptional over hundreds of thousands to millions of years, and to inform projections of future change.
History
Recognition of past ice ages in the nineteenth century launched the study of past climates, Milankovitch quantified the orbital theory in the early twentieth century, and the mid-twentieth-century advent of isotope analysis of deep-sea cores and ice cores transformed paleoclimatology into a quantitative science.
Debates
- Drivers of glacial terminations
- How orbital forcing, greenhouse gases, ocean circulation, and ice-sheet feedbacks combine to end ice ages, and which dominates, remains an active question.
Key figures
- Raymond Bradley
- Milutin Milankovitch
- Wallace Broecker
- Nicholas Shackleton
Related topics
Seminal works
- bradley2015
- cronin2010
Frequently asked questions
- How do scientists know about climates before thermometers?
- They read natural archives such as ice cores, tree rings, and sediments, whose chemical and biological signals act as proxies for past temperature, rainfall, and atmospheric composition.
- Why does the distant past matter for today's climate?
- Past climates show how sensitive the system is to changes in greenhouse gases and orbital forcing, giving independent checks on projections and showing that current changes are unusual.