How The Past Can Help Us To Predict The Future

By Katie Fawcett
March 2021

In the past 4.5 billion years of the earth’s history, a series of events have triggered changes in the climate, with wide ranging consequences. In this article I will explore introduce the concept of climate change, and discuss the triggers and implications of these past events. This information will be used to explore similarities between these events and the current climate crisis.

Setting the Scene: Climate Change and Changes in Global Temperature

Climate change is defined by the IPCC (2013) as “a change in the state of the climate which can be identified by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer”.

Scientists are able to identify changes in global temperatures by studying samples taken from:

• sediment cores,

• fossils,

• ice cores,

• pollen,

• tree rings,

• coral, and

• stalagmites.

These samples contain different chemicals or features which indicate the climate at a given time. For example, tree ring thickness shows whether the climate was warm and wet (wide ring) or dry (thin ring).  

Using this evidence, scientists have identified that temperature and greenhouse gas (GHG) emissions are linked (Figure 1), with the Earth going through natural cycles of warm and cool climates, punctuated by extreme events lasting millions of years. Since the industrial revolution, human emissions of GHG have dramatically increased which, according to the IPCC (2013) is the dominant cause of the recent observed warming.

Previous Extreme Events - The Five Mass Extinctions

There are known to have been five mass extinction events in the earth’s history, each lasting tens of millions of years. The geological time periods can be seen in Figure 2.

Early Warming Episodes: The Late-Devonian (383-359 million years ago (mya)), End-Permian (252 mya) and End-Cretaceous (66 mya) events were all warming episodes, caused by large volcanic eruptions which released huge volumes of GHG into the atmosphere. This caused warming of the atmosphere and oceans, along with ocean acidification and acid rain.

Great Species Decline: In the End-Permean event oceans reached 40°C near the equator. These events caused the extinction of 75-95% of plant and animal species. The End-Ordovician event (484 – 444 mya) was caused by a fall in temperatures, likely to have been triggered by the rise of the Appalacian Mountains in North America. This caused an ice age, trapping water in ice sheets and reducing sea levels, destroying shallow ecosystems and acidifying the oceans. 85% of species on the planet went extinct during this event.

The Extinction of the Dinosaurs: The End-Triassic (201 mya) is the most famous event which resulted in the extinction of the dinosaurs. This event is likely to have been caused by an asteroid, however there is also evidence of increased volcanic activity in the Deccan Flats in India at this time. The dust, debris and sulfur from the asteroid and the volcanoes blocked out the sunlight and is predicted to have caused a drop in global temperatures. There were also widespread wildfires and a large Tsunami at this time.  

More Recent Climate Events: 55.9 mya there was a warming event known as the Palaeo-Eocene thermal maximum (PETM) which lasted only 10,000 years and led to an increase of global temperatures of 5°C (Zachos et al 1993). This event caused Arctic sea temperatures to rise from 18°C to 23°C leading to sea level rise and a reduction in oxygen levels in the water (Sluijs et al 2006). This event is thought to have either been caused by volcanic activity along the North Atlantic ridge or by the release of methane deposits (Zachos et al. 2001). 41.5 mya there was another warming event likely to have been triggered by the collision of India and Asia known as the Middle Eocene Climatic Optimum.

The Mini Ice Age: Finally, the Younger Dryas Event, which was a mini-ice age approximately 12,500 years ago. This event was triggered very quickly, within 100 years and lasted for 1,300 years, followed by a period of rapid warming. It has been hypothesised that this event was caused by the melting of an ice sheet, depositing large amounts of fresh water into the sea, and disrupting the ocean currents.

 How does this compare to the current climate crisis?

Humans have emitted over 100 ppm of CO2 since 1850, during which time global average temperatures have increased by 1.1°C. This rate of warming is much faster than the rate of change in the events described above.

Humans have also been responsible for a range of other destructive activities such as deforestation, hunting, over-fishing, pollution, spreading disease and introducing invasive species. As extinctions are occurring hundreds of times faster than naturally, we could reach the level of a mass extinction in 240 to 540 years (Barnosky et al. 2011).

Sea levels are predicted to rise up to 50cm on average by 2100 as ice sheets melt and water expands (IPCC, 2013). There are also predicted to be an increase in extreme weather events including hurricanes and droughts, a reduction in reliable rainfall (impacting food supply), increased water shortages and increased climate migration. One other potential impact is that ocean circulation (which has already weakened 15% in the past 200 years) could be severely disrupted, causing increased storms, heatwaves and sea level rise, (Harvey. F. 2021) and could even lead to a cooling event similar to the Younger Dryas Event, although the IPCC (2013) classified this event as unlikely.

The devastating impacts of past climate events show us what the future could look like if we don’t stop emitting large volumes of GHG into the atmosphere. This highlights the importance of working together to quickly develop sustainable solutions and to protect forests, oceans and nature for future generations, and to prevent the further extinctions.

You May Also Be Interested In:  The Intergovernmental Panel on Climate Change – who are they and what to do they do?, The Search for Planet B? How Space Exploration Provides Solutions to Climate Change, More Heat, Less Eat - Why Nutrition Suffers Due to Climate Change

References:
Barnosky, A., Matzke, N., Tomiya, S. et al. Has the Earth’s sixth mass extinction already arrived?. Nature 471, 51–57 (2011). https://doi.org/10.1038/nature09678
Harvey, F., 2021. "Atlantic Ocean circulation at weakest in a millennium, say scientists". The Guardian. Retrieved 2021-02-27.
IPCC, 2013. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovern- mental Panel on Climate Change. Edited by Stocker, TF, Qin, D, Plattner, GK, Tignor, M, Allen, SK, Boschung, J, Nauels, A, Xia, Y, Bex, V and Midgley, PM, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Sluijs, A., Schouten, S., Pagani, M., and Woltering, M., 2006. Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum. Nature. 441(7093):610-3
Zachos, J.C., Lohmann, K.C., Walker, J.C.G., and Wise, Jr., S.W., 1993. Abrupt climate changes and transient climates during the Paleogene: a marine perspective. J. Geol., 101:191–213.
Zachos, J.C., Pagani, M., Sloan, L., Thomas, E., and Billups, K., 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science, 292(5517):686–693.
https://www.nationalgeographic.com/science/article/mass-extinction
https://www.amnh.org/exhibitions/dinosaurs-ancient-fossils/extinction/mass-extinction#:~:text=The%20extinction%20that%20occurred%2065,beginning%20of%20the%20Tertiary%20period.

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