As the second most prevalent greenhouse gas in our atmosphere (after water vapour), carbon dioxide (CO2) has become a crucial indicator of climate change. Throughout the Earth's 4.54 billion-year history, CO2 levels have fluctuated significantly, contributing to our planet's average temperature shifts. The Evolution of CO2 Scientific consensus currently explains the development of our atmosphere in three stages. First, during the formation of the Earth, our solar system contained high concentrations of helium and hydrogen, which circulated at extremely high temperatures. Over time, these molecules escaped into space, and a new atmosphere emerged through volcanic emissions. Next, eruptions released water vapour, CO2, and ammonia (composed of one nitrogen and three hydrogen atoms), forming a gaseous blanket above and water bodies below. Finally, CO2 slowly dissolved into the shallow oceans, allowing cyanobacteria to carry out oxygen-emitting photosynthesis. As the oxygen accumulated, the atmospheric composition changed enough to cause the extinction of most microorganisms present at that time, approximately 2.4 billion years ago. CO2 and Previous Climates For reference, pre-industrial CO2 levels were around 280 parts per million (ppm), whereas today, we find ourselves nearing 420 ppm. The furthest period for which we have estimated CO2 levels is around the Ordovician period, 500 million years ago. During that time, atmospheric CO2 concentration ranged from a staggering 3000 to 9000 ppm! Despite this high concentration, the average temperature was not much higher than today's. Those familiar with the concept of a runaway hothouse Earth scenario might wonder why it did not occur back then. Significant factors include the Sun being cooler and the different orbital cycles of the planet. Historical CO2 Levels Graph depicting CO2 levels over the past 500 million years. Foster et al. – Descent into the Icehouse. CO2 levels are influenced by the balance between carbon sequestration (burial in sediments, plant capture) and carbon emissions (decomposition and volcanic activity). Imbalances in this system led to a decline in CO2 levels, resulting in a glaciation period approximately 300 million years ago. This was followed by intense volcanic activity, doubling CO2 concentration to about 1000 ppm. Subsequently, CO2 levels decreased until they reached the concentrations observed today during the Oligocene era, 33 to 23 million years ago, when temperatures were still 4 to 6 degrees Celsius higher than current levels. CO2 levels shaped history and the types of climates that prevailed. This is a concerning reality, as the greenhouse gas emissions we have released may lead us back to similar conditions. CO2 Data from Ice Cores: Undoubtedly, the climate is an incredibly intricate system with numerous incompletely understood factors. Consequently, caution is necessary when interpreting such statements. Moreover, the further we delve into the past, the greater the uncertainty surrounding the data. However, concrete evidence spanning the last 800,000 years is available, thanks to ice cores that offer detailed records of trapped air bubbles within frozen snow. CO2 Data from Ice Cores for the Past 800,000 Years: Reliable CO2 data from ice cores encompassing the previous 800,000 years. Source: climate.nasa.gov The Highest CO2 Levels in Recent History: We employ this data as a benchmark for comparative analysis. Sources:
https://earth.org/data_visualization/a-brief-history-of-co2/ by Owen Mulhern By Glen Fergus – Own work; data sources are cited below, CC BY-SA 3.0,https://commons.wikimedia.org/w/index.php?curid=1240577 https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere
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