Introduction: How Earth’s Temperature Has Changed Over the Past 500 Million Years
Earth’s temperature has changed a lot over the last 500 million years. A recent study created a new temperature curve, showing that our planet’s temperature has varied more than scientists previously thought. This period is called the Phanerozoic Eon, and it’s known for the rise of many different life forms, the spread of life onto land, and multiple mass extinctions.
The study also confirmed a strong connection between Earth’s temperature and the amount of carbon dioxide (CO2) in the atmosphere. By understanding these changes, scientists hope to learn more about how our climate might change in the future.
The Phanerozoic Eon: 500 Million Years of Change
The Phanerozoic Eon started about 540 million years ago with the Cambrian Explosion, a time when complex life forms first appeared. This period saw a big increase in the diversity of life, with many different species evolving. The study, however, focuses on the last 485 million years, as it’s hard to find rocks older than that with temperature data. These ancient rocks serve as geological proxies, meaning they help scientists understand past climate patterns.
Jessica Tierney, a paleoclimatologist at the University of Arizona, explains, “We don’t have many rocks from 485 million years ago with temperature indicators, so it’s difficult to go back any further.”
Creating the Temperature Curve
The researchers used a method called data assimilation to develop a new curve showing how Earth’s temperature has changed. Data assimilation combines real-world data from rocks and fossils (geological proxies) with computer simulations of the climate. This approach, originally used for weather forecasting, now helps scientists study ancient climate patterns.
Emily Judd, the lead author of the study and a former researcher at the Smithsonian National Museum of Natural History, said, “Instead of forecasting the weather, we’re hindcasting ancient climates.”
This method allows scientists to recreate temperature fluctuations over millions of years. The result is a detailed temperature curve showing the highs and lows of Earth’s climate history, including periods of extreme heat and cold.
CO2: The Biggest Driver of Earth’s Temperature
The study reveals that carbon dioxide (CO2) levels are the main factor affecting Earth’s temperature across the Phanerozoic Eon. When CO2 levels were high, the planet was warmer, and when CO2 levels were low, the planet was cooler. Over the past 485 million years, Earth’s temperature ranged from 52 to 97 degrees Fahrenheit, which is a 45-degree span. These findings support the idea that greenhouse gases, especially CO2, play a huge role in global warming trends.
“This research shows that CO2 is the dominant control on global temperatures across geological time,” Tierney said. “When CO2 is low, the temperature is cold; when CO2 is high, the temperature is warm.”
Scientists also found that the climate sensitivity to CO2 has remained steady over millions of years. Climate sensitivity measures how much the temperature increases when CO2 levels double. In this case, it was about 8°C for every doubling of CO2, which is higher than today’s sensitivity.
Studying Ancient Climate Patterns
Understanding Earth’s ancient climate patterns helps us predict future climate change. The researchers used fossilized shells, coral, and other ancient organic materials as temperature indicators. These materials helped the team estimate temperatures from different time periods and create a more accurate picture of how Earth’s temperature has changed.
In addition to fossil data, researchers from the University of Bristol ran over 850 climate model simulations to understand how Earth’s temperature changed over time. These simulations took into account factors like continental positions and atmospheric composition, helping scientists understand how CO2 levels and other elements influenced Earth’s climate history.
The Impact of Polar Amplification
Another important finding from the study was the concept of polar amplification. This means that temperature changes were more extreme at the poles than at the equator. As the temperature changed over millions of years, the difference between temperatures at the poles and the tropics also shifted.
For example, during warm periods, the poles were much warmer than today. This change in the tropical-to-polar temperature gradient played a big role in Earth’s climate history and influenced how different species adapted or went extinct.
Mass Extinctions and Climate Change
The Phanerozoic Eon had multiple mass extinction events, and many were linked to rapid temperature changes and high CO2 levels. When Earth’s temperature quickly increased, many species could not adapt fast enough and died out. This included marine animals, plants, and even some early land animals.
For example, the end-Permian extinction, which happened about 252 million years ago, was one of the most significant extinction events. It was caused by volcanic eruptions that released massive amounts of CO2, leading to extreme global warming. This rapid warming event was much faster than natural warming events, causing widespread extinction.
Comparing the Past to Today’s Climate
The study shows that Earth’s current global temperature of 59 degrees Fahrenheit is cooler than it was for most of the Phanerozoic Eon. However, today’s climate is warming at a much faster rate than ever before. Human activities, like burning fossil fuels, are releasing large amounts of CO2, causing rapid climate change. This is similar to past events when CO2 levels increased quickly, but today it’s happening at an even faster pace.
Scott Wing, a co-author of the study, noted, “If you’re studying the last couple of million years, you won’t find anything that looks like what we expect in 2100 or 2500.”
To understand how Earth’s climate might change in the future, scientists need to look at times when the Earth was much warmer than it is today.
The Importance of Climate Sensitivity
One of the most critical findings from this study is the idea of climate sensitivity. This refers to how much Earth’s temperature changes in response to CO2 levels. According to the study, climate sensitivity has remained consistent over the past 485 million years. This means that even when the planet was much hotter or colder than today, CO2 was still the main driver of temperature changes.
By studying ancient climates, scientists hope to understand how our current climate might respond to rising CO2 levels. Knowing that CO2 has always been a key factor in temperature changes helps researchers predict how much warming we might expect in the future if CO2 levels continue to rise.
What Does This Mean for Us Today?
Humans have evolved in a relatively cool period of Earth’s history, with temperatures ranging within a 10-degree Fahrenheit span. However, over the Phanerozoic Eon, temperatures have ranged up to 45 degrees Fahrenheit. This shows that the climate we are used to is not typical of Earth’s long-term history.
“We are changing the climate into a place that is really out of context for humans,” said Tierney. Rapidly warming temperatures could spell danger for humans and animals because many species, including humans, cannot adapt to fast changes. This is why understanding Earth’s past climate is so important—it can help us prepare for future changes.
How Scientists Created the Most Accurate Curve Yet
The collaboration between paleoclimatologists at the University of Arizona and the Smithsonian began in 2018. They collected more than 150,000 estimates of ancient temperatures using five different chemical indicators found in fossilized shells and other organic matter. These indicators helped create the most accurate curve of Earth’s temperature changes over the last 485 million years.
By combining these estimates with climate model simulations, scientists developed a detailed understanding of how CO2 levels, solar luminosity, and trace greenhouse gases have affected Earth’s climate.
The Role of Planetary Albedo and Greenhouse Gases
The study also highlights how planetary albedo, which is the amount of sunlight Earth reflects back into space, and trace greenhouse gases helped regulate Earth’s temperature over millions of years. When CO2 levels were high, more heat was trapped in the atmosphere, leading to warmer temperatures. When CO2 levels dropped, the Earth reflected more sunlight, causing the planet to cool.
Final Thoughts
Understanding how Earth’s temperature has changed over the past 500 million years helps scientists predict how the climate might change in the future. The strong connection between CO2 levels and global mean surface temperature (GMST) shows that carbon dioxide is the biggest driver of climate change. As we continue to release CO2 into the atmosphere, we may be pushing Earth into a climate state that hasn’t existed for millions of years.
By looking at ancient climate patterns, studying the effects of polar amplification, and understanding climate sensitivity, researchers can learn valuable lessons that may help us face the challenges of today’s climate crisis.