Carbon serves as the fundamental foundation of life on Earth. Everything around us—what we eat, our civilization, and even ourselves—is intricately linked to carbon. While our reliance on carbon is essential, this necessity is intricately connected to one of the most pressing challenges of our time: global climate change.
Born in the fiery cores of aging stars, carbon stands as the fourth most abundant element in the Universe. Most of the Earth’s carbon, approximately 65,500 billion metric tons, is stored in rocks. The remaining carbon is distributed across the ocean, atmosphere, plants, soil, and fossil fuels. The carbon cycle is the flow of carbon between these reservoirs including both slow and fast components. Shifting carbon out of one reservoir increases carbon levels in other reservoirs. Changes introducing carbon gases into the atmosphere lead to elevated temperatures on Earth.
Over a long time, the carbon cycle does a balancing act to make sure all of Earth’s carbon doesn’t end up in the air like on Venus or get stuck entirely in rocks. It’s like a thermostat that helps keep Earth’s temperature steady. My first article in this series will describe how the carbon cycle has operated in Earth’s history.
Shifts in the movement of tectonic plates and variations in the rate at which carbon releases from the Earth’s interior played a role in adjusting the temperature on the planetary thermostat. Earth has experienced such adjustments over the last 50 million years, transitioning from the notably warm climates of the Cretaceous era (approximately 145 to 65 million years ago) to the icy conditions of the Pleistocene epoch (approximately 1.8 million to 11,500 years ago).
Throughout Earth’s history, the carbon cycle has transformed in response to shifts in climate. Changes in the planet’s orbit, influenced by factors like those studied by Milutin Milankovitch, have played a role in altering the Sun’s energy reaching Earth. This, in turn, triggers cycles of ice ages and warm periods, mirroring the current climate.
During ice ages, when Northern Hemisphere summers cooled and ice accumulated on land, the carbon cycle experienced a slowdown. Various factors, including cooler temperatures and increased growth of phytoplankton, likely enhanced the ocean’s ability to absorb carbon from the atmosphere. The reduction in atmospheric carbon, in turn, contributed to additional cooling. Conversely, at the conclusion of the last Ice Age around 10,000 years ago, there was a significant rise in atmospheric carbon dioxide as temperatures warmed. These historical patterns underscore the intricate relationship between Earth’s climate, the carbon cycle, and the complex interplay of environmental factors over time.
Earth’s orbit undergoes continuous, predictable cycles, with shifts occurring regularly. In approximately 30,000 years, the alterations in Earth’s orbit will reach a point where sunlight in the Northern Hemisphere decreases to levels reminiscent of the conditions that led to the last ice age. Today, changes in the carbon cycle are primarily driven by human activities. The combustion of fossil fuels and the clearing of land disrupt the natural balance. When forests are cleared, the dense growth of plants, storing carbon in wood, stems, and leaves (biomass), is removed. This means we eliminate the very plants that would naturally absorb carbon from the atmosphere as they grow. Often, the cleared areas are replaced with crops or pasture, which store less carbon. Additionally, exposing the soil releases carbon from decomposed plant matter into the atmosphere. Human activities related to land use changes currently contribute to the release of just under a billion tons of carbon into the atmosphere each year. These actions highlight the significant impact of human behavior on the delicate carbon cycle.
Since the start of the Industrial Revolution, the levels of carbon dioxide in the atmosphere have increased. Starting at approximately 280 parts per million, these concentrations have now reached 412 parts per million, representing a significant 47 percent increase. To put it into perspective, this means that out of every million molecules in the atmosphere, 412 are now carbon dioxide—the highest concentration observed in the past two million years. In my next blog, I’ll discuss how the carbon cycle interacts with our oceans.
Photo by Guillaume Falco via Pexels
