Paleoclimatology is the study of Earth’s past climates. A related field to paleoclimatology is paleoceanography, which is the study of Earth’s past oceans, currents, chemistry, biology, and the distribution of ocean sediments. For simplicity, we will talk about both paleoclimatology and paleoceanography under the broader term paleoclimatology.

Climate vs. Weather

Before we move on to talk about climate, it’s important to make a clear distinction between climate and weather. Too often, these two words are used interchangeably in the news and on social media. Climate is the long-term changes Earth experiences within a region, whereas weather are the short-term changes in the atmosphere that occurs on an hourly or daily basis. You can think of your mood as weather, but your personality would be climate. Typically, scientists study climate due to the resolution of our rock and sediment record. In other words, we cannot resolve the weather of any one particular day or week millions of years ago.

Why study past climates and oceans?

Life is only possible because of our oceans, as the first life forms (single-celled microbes) evolved there more than 3.5 billion years ago. Today, the oceans are still harbingers of a huge diversity of organisms. But they also serve to moderate climate through heat transport, heat absorption, and CO₂. The atmosphere (the area above the ocean that contains oxygen and all other gases) exchanges heat, water vapor, and CO₂ with the ocean, thus the two are very intimately connected.

Past conditions of climate and the oceans are very important to understand, because they can tell us something about how future climate and oceans will react to increasing levels of CO₂ due to human activities. And it’s not just the climate we’re concerned with: scientists also study past states of the oceans and their biology to understand how organisms will respond to warming of the Earth. In addition, some scientists model what will happen to climate and the oceans under different greenhouse gas scenarios (for example, elevated CO₂ conditions). In order to make the models as correct and robust as possible, climate modelers rely on data from paleoceanographers and paleoclimatologists. For example, if a climate model is not predicting that Antarctic ice would melt at elevated CO₂ conditions, but the data from paleoceanographers indicates that it did, then the models might be missing a variable, or a variable may not be quite right. Therefore, the model must be adjusted to properly model future climate scenarios.

What do Paleoclimatologists do?

Paleoclimatology and paleoceanography are both huge fields of study with the broader field of geology. Paleoclimatologists and paleoceanographers use rocks and sediments to reconstruct past climate and ocean conditions on Earth anywhere from millions of years ago to thousands of years ago. We study the rock record, sediments drilled from the seafloor, and sediments taken from lakes. Because we can’t directly measure past climate conditions, we use different proxies to reconstruct climate. Proxy data are physical characteristics of the environment that are preserved, and which can be used as a direct measurement of climate conditions.

To learn more about different types of proxies, check out the “Proxy Data” page.

Currently, many scientists who work in the field of paleoclimatology are trying to reconstruct ancient CO₂ amounts, as well as estimate the temperature of our oceans and land. To do this, we rely on several types of data obtained from proxies. there are several ways to estimate and measure temperatures and the amount of CO₂ in deep time, but we will talk about the most common types of data, such as isotopes of oxygen and carbon, measured from the calcite shells of marine plankton.