Past Climate

Hot, cold, windy, dry – all are terms used to describe climate in different places on Earth over time. From Ice Ages to Hothouses, global and regional climate has changed on very long time scales, and many of the changes are recorded by natural processes. 

How Do We Study the Climate of the Past?

Paleoclimatology is the study of climate records from hundreds to millions of years ago. Paleoclimate data come from climate records found in nature. They are known as proxy records or indirect records of climatic conditions. Descriptions of past climates can be found at NOAA Paleoclimate »

How Do Scientists Interpret Natural Records?

Coring a Tree

Coring a tree to gain access to tree ring data. 
Image source: Penn State Department of Meterology

While we don't often think about it, weather is constantly shaping our environment. Everything in nature, from river sediments to plant growth and distribution, is influenced by weather and climate. The most easily recognized type of paleoclimate record is tree ring data. Other common sources of proxy data for climate include lake and ocean sediments, layers of ice (cored from ice sheets), corals, fossils, and historical records from ship logs and early weather observers.

Paleoclimate records come from all around the world – from the tops of mountains, to the bottom of the ocean, from the tropics to the poles. [insert map of data record locations from NOAA maps and data integrated map app]

Scientists use a variety of methods to access and analyze climate proxies. The most familiar methods involve taking a core sample of tree rings, corals, sediments, and ice. By measuring the width, chemical composition, and physical structure of each layer, scientists can deduce the conditions present when each layer formed. Examples of paleoclimate data »

Another way to learn about past climate is to take the temperature of rocks at different depths via boreholes drilled directly into the Earth’s crust. Rocks respond very slowly to different temperature conditions, and deeper rocks change temperatures more slowly than shallower rocks. Precise measurements of the rate of temperature change of rocks at various depths can be correlated to past temperatures at the surface.

More about boreholes, including links to borehole data:
NOAA Borehole data »
University of Michigan Borehole Information »

What Can I Do with Paleoclimate Data? What is it Good For?

Records of past climate provide context for present climate. For instance, one might ask, “How does the drought in the western United States this year compare with droughts of the recent and ancient past?” By analyzing tree rings and sediments from lakes and dunes, scientists can reconstruct the history of drought, and compare the severity and extent of present conditions to droughts of the past. These sorts of comparisons are invaluable for water and other resource managers when they plan for the future.

Climates of the Past

Paleoclimate records, collected by independent science teams worldwide, become even more valuable when plotted and compared with one another. As the following graph of past temperatures indicated by various methods shows, common patterns of temperature trends are broadly consistent across a variety of data collection methods. By comparing multiple sets of proxy records, scientists have been able to reconstruct a fairly consistent story of Earth’s climate for the past few thousand years. While the methods of calculating global average temperature from different proxies vary from team to team, the outcomes are broadly consistent over time, and converge with the instrumental record. The broad agreement of several datasets increases our confidence that proxies reveal valid temperature records.

NH Climate Reconstruction

Northern Hemisphere Climate Reconstruction
Image source: IPCC WG 1 figure 6.10


References and Further Information

More information and access to datasets
NOAA Paleoclimatology » 

Learn more about the tools and methods that are used in past climate research
Paleoclimate Education and Outreach »

Significant droughts of the past are recorded in paleoclimate data. Read more about past droughts and access drought data at the following links: