• sciandenvironment

Messages from the past: ways to predict what our changing climate will look like

Evidence of what the climate was like thousands of years ago can be found across nature, providing much needed information on the effects of a changing climate.

By Lily Steel

Photo courtesy of Couleur from Pixabay.

One of the best ways to predict the future is to look at trends from the past. This concept underlies the science of paleoclimatology - the study of past climates. Temperature changes that have previously occurred over a millennium have occurred rapidly over recent decades. The global temperature is now warmer than any time in the last 120,000 years. The last warm period was due to the Earth’s axis shifting and orbit changing, whereas today it is due to rising carbon levels in the atmosphere. One study has shown that the atmospheric concentration of carbon dioxide in the atmosphere today is greater than at any time in the past two million years. The technological advancements since the industrial revolution have led to great human progress, but they have also led to carbon emissions increasing at a terrifying rate, destroying our climate. Hope can be found in new methods to study what Earth’s climate looked like throughout its history, as we can use this to predict the climate of our future.

Small air bubbles become trapped when snow falls heavily and then compresses. This forms polar ice sheets that act as permanent records of what the climate was like thousands of years ago. These ice sheets form in layers, so ice from deeper down holds air from older climates. The age of this air can be quite accurately estimated up to 800,000 years ago, and the tiny bubbles of past climates can be analysed in laboratories to determine the concentration of greenhouse gases they contain. The amount of oxygen, carbon dioxide and methane can tell us how warm the atmosphere was at the time the air was trapped, giving us a good idea of the trends in temperature change up till now.

Tree rings are a useful indicator of recent climate history. The annual rings that form in the trunk can differ in width, density and colour, all indicators of what the climate was like that year.

Tree rings are a useful indicator of recent climate history. The annual rings that form in the trunk can differ in width, density and colour, all indicators of what the climate was like that year. Trees can be found all over the world and historic tree samples can be found in preserved historical artefacts like churches and boats. It is mostly tree ring data that helped uncover the medieval climate anomaly, where Europe was uncharacteristically warm in the Middle Ages and the Dantean anomaly where, around 1310, wet summers resulted in crop failure that killed off a sixth of the European population. Fluctuations of the climate in the past will help us predict and prepare for such events in our future.

Tiny fossils preserved in the seabed can also be good indicators of past climates. The comprising elements of fossil shells are related to the amount of carbon dioxide that was in the ocean when the organism was alive. The ratio of different element isotopes can also be used. Isotopes are atoms of elements that can be heavier or lighter depending on the number of neutrons they have. For example, oxygen has two very common isotopes in nature, Oxygen-16 and Oxygen-18. In colder climates more Oxygen-18 can be found in ocean water as lighter Oxygen-16 more readily freezes into sea ice. So, fossils that have more Oxygen-18 in their chemical make-up must have been alive in cooler climates. Fossilised coral can be particularly useful as it lives for many years and grows in rings. Each ring can be analysed for its isotope ratio and used to detect small changes in the climate from thousands of years ago.

Climate change is a ‘natural’ process that has occurred ever since there has been a climate on Earth. But studies of the climate in the past have revealed that the rate at which the atmosphere is warming is unprecedented, and all evidence points to human activity. The carbon released today will stay there for hundreds of years, the effects cannot be quickly reversed or halted, so there is no doubt we will have to live with challenges of a changing climate. Hopefully this form of science can be used to help us predict what will happen in the near future and hopefully spur world leaders into taking some real action in preventing the climate disasters that we are already witnessing across the globe. After all, Earth will survive a changing climate but life as we know it will not.