See how we screwed up the Earth's climate in 160 years

The consequences are imminent.

Guillaume Paris, a geochemist, is a researcher at the Nancy Centre for PetroGeochemical Research, University of Lorraine, France, and the National Centre for Scientific Research, France

Pierre-henri Blard, geologist and paleoclimatologist, is a Research fellow at the Research Centre for Lithofacies and Geochemistry (Nancy) and the GlacialLaboratory (Brussels) of the University of Lorraine, France, and CNRS

Climate change is arguably the most pressing issue of the day, both politically and in terms of survival. The perception that climate change is the result of popular action is also growing.

For 11,500 years, the concentration of carbon dioxide in the atmosphere hovered around 280 parts per million (parts per million; Pre-industrial "normal"), the average surface temperature is about 15 degrees Celsius. Since the start of the Industrial Revolution, this level has continued to rise, reaching 410ppm in 2018. Earth scientists have focused on timelines stretching back billions of years, using special instruments to demonstrate with extraordinary clarity how suddenly industrial societies have changed and are changing the Earth's climate.

Climate, greenhouse gases and carbon dioxide

The main engine of the Earth's climate is the sun. Our star has an average surface power of 342 watts per square meter per year (roughly equivalent to one hair dryer per square meter on the planet). The Earth absorbs about 70 percent and reflects the rest away. If this were the only climate mechanism, the average temperature would be -15°C (0°C below the freezing point of water). Life would be impossible. Fortunately, some of the absorbed energy is in turn reflected back as infrared radiation, which, unlike visible light, interacts with greenhouse gases (GHGs) present in the atmosphere to radiate heat back to the Earth's surface. This greenhouse effect currently keeps our average temperature around 15°C.

The main greenhouse gases are water vapor and controversial carbon dioxide. Carbon dioxide accounts for 30 percent of the greenhouse effect, while water vapor contributes the remaining 70 percent, but carbon dioxide has the overall warming power that water vapor does not. Water vapor stays in the atmosphere for a short time (on the order of a few hours to a few days) and only increases in concentration as the temperature increases. Carbon dioxide can linger in the atmosphere for 100 years, its concentration independent of temperature control. So carbon dioxide is the main cause of warming: if carbon dioxide concentrations increase, average temperatures will increase regardless of the trend.

Carbon sequestration

Understanding the regulation of carbon dioxide in the atmosphere is crucial. On geological time scales (over 100,000 years), volcanic gases are the main source of co 2, with an average of 400 million tons of co 2 (0.4 GtCO2/y) escaping in this way each year. But carbon dioxide isn't just accumulating in the atmosphere. Due to other environmental processes, carbon dioxide can accumulate and disperse and be stored as carbon sinks.

For example, the ocean contains 50 times more carbon than the atmosphere. However, carbon dioxide dissolved in the oceans is easily released into the atmosphere, and only geological deposits on geological timescales can keep carbon dioxide out of the atmosphere.

The first geological deposition was the deposition of organic matter. Living organisms contain organic carbon built from atmospheric carbon dioxide through photosynthesis, and dead organisms are often sent to the bottom of oceans, lakes and swamps. As a result, large amounts of organic carbon accumulate in ocean and continental sediments over time, some of which is eventually converted to fossil fuels (oil, gas, and coal).

Calcareous rocks are a second geological carbon sink. Rocks such as granite or basalt are flooded by surface water, and calcium and bicarbonate ions are washed out into the ocean. Marine life uses them to build hard parts made of calcium carbonate. When deposited on the ocean floor, the calcium carbonate eventually sequesters to form limestone.

Together, these two deposits (sinks) are estimated to be 50 to 100, 000 times the amount of carbon currently stored in the atmosphere.

Earth's atmosphere in time lapse

The amount of carbon dioxide in the Earth's atmosphere varies widely. Decades of research have allowed us to map the main line of history after the Earth was fully born 4.4 billion years ago.

Earth's early atmosphere was rich in carbon dioxide (nearly 10,000 times today's level), and oxygen was scarce. In the Archean (3.8-2.5 billion years ago), life first erupted and the first continents arose. Weathering begins to release carbon dioxide into the atmosphere. The development of photosynthesis helped to reduce carbon dioxide in the atmosphere, and it also boosted oxygen levels around 2.3 billion years ago during the Great Oxidation Event (a sudden increase in free oxygen in the atmosphere for unknown reasons, but which made possible the emergence of later animals). Carbon dioxide concentrations fell to levels "only" 20-100 times pre-industrial levels, never returning to the earliest concentrations on Earth.

Two billion years later, the carbon cycle has changed. Back in the Late Devonian to Early Carboniferous period (about 350 million years ago), carbon dioxide concentrations were about 1,000 parts per million and mammals did not exist. Vascular plants capable of synthesizing lignin, a complex organic polymer that is an important structural material for vascular plants and algae and is particularly important in cell wall formation, appeared in the Devonian period and later. Lignin is a microbiotically resistant molecule that allows large amounts of organic carbon to form coal over millions of years. Combined with the weathering of the Hercynian (the late Paleozoic era named after the Hercynian mountains in Germany where the crust moved to form folds), the remains of which can be found in the Central Plateau of France or the Appalachian Mountains in the United States, organic carbon burial reduced atmospheric carbon dioxide to levels similar to (or even lower than) today, And contributed to the ice Age between 320 and 280 million years ago.

At the end of the Jurassic period (145 million years ago), however, the pendulum swung. Dinosaurs ruled the Earth, mammals evolved, tectonic activity increased, and Pangaea, the last supercontinent, was torn apart. Carbon dioxide increased to 500-2000 PPM and stayed at this high level, maintaining a warm greenhouse climate for about 100 million years.

Beginning 55 million years ago, the Earth cooled as carbon dioxide decreased, especially after the Himalayan uplift and subsequent deposition of weathering and organic carbon. Evolution has continued since humans emerged seven million years ago. For 2.6 million years, the Earth entered a new state characterized by alternating glaciations with interglaciations guided by Earth's orbital parameters and amplified by short-term carbon cycles. When the Earth entered its latest interglacial phase 11,500 years ago, carbon dioxide reached pre-industrial levels.

A whole new story: The Industrial Revolution

Until the 19th century, the story of carbon in the atmosphere and the Earth's climate was nothing more than the story of geology, biology and evolution. The story changed dramatically after the Industrial Revolution, when modern humans (late Homo sapiens) began mining and burning fossil fuels on a massive scale about 300,000 years ago.

By 1950, the increase in carbon dioxide in the atmosphere through the burning of fossil fuels was confirmed by the carbon isotope characteristics of carbon dioxide molecules (the "Seuss effect", also known as the industrial effect, refers to the imbalance of carbon 14 and carbon 12 in the atmosphere caused by the massive burning of fossil fuels since the industrial era). By the late 1970s, climatologists had observed an acceleration in the overall warming trend. The Intergovernmental Panel on Climate Change (IPCC), a United Nations intergovernmental body founded in 1988 in collaboration with the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), based in Geneva, Switzerland, said in 2012 that the average temperature had risen by 0.9 ° C since 1901. That may not seem like a big change from the last time the ice retreated, when average temperatures rose by 6 ° C in the last 7,000 years, but the rate of change has accelerated by at least 10 times.

Average temperatures continue to climb, and natural parameters such as solar activity or volcanic activity cannot explain this rapid warming. The reason is that humans are explicitly adding greenhouse gases to the atmosphere, and high-income countries emit the most greenhouse gases per inhabitant.

How will our story end?

Industrial societies have burned about 25 per cent of the Earth's fossil fuels in 160 years, and have suddenly encouraged the release of stored carbon into the atmosphere, disrupting natural fluxes. This new anthropogenic flux adds 28Gt (gross tons) of carbon dioxide per year, 50 times more than volcanoes. Natural geological sequestration cannot balance the increase, and atmospheric carbon dioxide continues to rise.

The consequences are imminent, unprecedented and appalling: extreme weather events, rising sea levels, retreating glaciers, ocean acidification, destruction and extinction of ecosystems. Earth has survived other disasters. Although current warming will exceed the capacity of many species to adapt, life will go on. Not that the planet is in danger, but that the future of human society and the current conservation of ecosystems are in dire straits.

While earth sciences cannot provide solutions to think about all that must change in our behavior and fossil fuel consumption, they can and must contribute to the current rise in knowledge and collective awareness of global warming.