Global challenges Study Guide

The Earth's climate is influenced by greenhouse gases such as carbon dioxide (CO₂) and methane (CH₄). These gases naturally trap some of the Sun's energy in the Earth's atmosphere, preventing it from escaping back into space. This natural process is called the greenhouse effect and is essential for maintaining temperatures suitable for life on Earth. However, human activities have significantly increased the concentrations of these gases, leading to an enhanced greenhouse effect. When CO₂ levels rise, primarily from the burning of fossil fuels (coal, oil, and natural gas) for energy, transportation, and industrial processes, more heat is trapped. Similarly, increased methane levels, often from agriculture (livestock farming, rice cultivation), landfill sites, and the extraction of fossil fuels, also contribute significantly to heat trapping. The key effects of these increased levels include a rise in global average temperatures, known as global warming. This warming can lead to melting glaciers and ice caps, contributing to rising sea levels. Other consequences include more frequent and intense extreme weather events such as heatwaves, droughts, floods, and storms, which can disrupt ecosystems, agriculture, and human settlements. Changes in precipitation patterns can lead to water shortages or excessive rainfall in different regions. Ocean acidification also occurs as oceans absorb excess CO₂, harming marine life, particularly organisms with shells or skeletons made of calcium carbonate. Mitigating these effects involves reducing greenhouse gas emissions through various strategies, including transitioning to renewable energy sources (solar, wind), improving energy efficiency, carbon capture and storage technologies, adopting sustainable agricultural practices, reducing deforestation, and promoting international cooperation to set emission targets.

The early atmosphere of planet Earth formed around 4.5 billion years ago, initially composed primarily of hydrogen and helium from the solar nebula. However, these light gases were stripped away by the solar wind because Earth lacked a strong magnetic field at that time. A secondary atmosphere then developed through intense volcanic activity. Volcanoes released significant quantities of gases, including carbon dioxide, water vapour, and nitrogen, along with smaller amounts of methane and ammonia. As Earth cooled, the water vapour condensed to form oceans. Carbon dioxide dissolved in these oceans, leading to the formation of sedimentary rocks like limestone and the uptake by early marine organisms. Nitrogen, being relatively unreactive, gradually built up in the atmosphere, eventually becoming its most abundant gas. It's crucial to understand that there is no definitive, universally accepted model for all stages of atmospheric evolution, but the volcanic outgassing theory is the most widely supported explanation for the formation of the secondary atmosphere.