What can we learn about climate change by studying the climate of the past?
Predicting the weather is a complex science and predictions become less accurate as the range of the forecast increases. So how have scientists managed to learn what the climate – the average weather- was millions of years ago? And why is this important today? Scientists convened at the Smithsonian National Museum of Natural History last spring to piece together what the climate was like throughout Earth’s history going back millions of years. Their findings not only help explain paleoclimate, but they also provide useful models to understand and predict present and future climate change.
Scientists have a wide array of models and proxies at their disposal to study ancient climates. For example, models can be used to simulate the weather millions of years ago. Paleoclimate models for the late Jurassic, 150 million years ago, may use changes in solar constant, continental configuration and the amount of carbon dioxide providing a kind of weather forecast for dinosaurs. These can be averaged to approximate the climate of the time.
Just as the archeologist studies artifacts, paleoclimatologists study different types of environmental evidence to reconstruct previous climates. Fossilized plankton contain evidence of the environment in which their shells were formed and the chemical composition of the shells alters according to temperature. In this way, ocean temperatures are imprinted in the fossil records and can be read using chemical analysis.
Similarly, skeletonized marine invertebrates, for example clams, snails and coral, also reflect the environment in which they develop. In analyzing their chemistry, approximates of the temperatures in which they grew can be recovered. Growth rings, like the rings of a tree, show development over a number of years. Variances in the chemical composition between consecutive rings illustrate seasonal variation. Thus, we can get a picture of how hot the summer was and how cold the winter was millions of years ago.
The scientists and climate modellers who convened in the Spring 2018 were able to combine their research to create a graph that shows how climate and temperature changed throughout Earth’s history.
But how does looking back millions of years help us predict future climate? For one, these studies provide evidence of how different climatic factors come together and their various consequences. For example, scientists study the fluctuations of carbon dioxide over time to understand the effects of carbon dioxide on climate and sea levels. In the Devonian era 400 million years ago, carbon dioxide levels were approximately four times what they are today. Carbon dioxide levels similar to those observed today were last seen 3 million years ago – a time when there was no ice on Greenland. The last time carbon dioxide levels were as high as scientists predict they might be by the end of the century, there was no ice in Antarctica - this would produce a 60 m difference in ocean levels (approximately 197 ft.). By reconstructing historical climate change paleobiologists provide a model for us to understand different environmental processes and predict the effects of future climate change.
Funding for the Earth’s Temperature Curve Symposium, on which this article is based, was provided by Roland and Deborah Sauermann.