This chapter, authored by a team of international experts, provides a comprehensive overview of the biogeochemical cycles of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). It addresses the historical changes in these greenhouse gases, their sources and sinks, and their impacts on climate change. The chapter highlights that CO₂, CH₄, and N₂O have increased significantly since the pre-industrial era due to anthropogenic activities, particularly fossil fuel combustion and land use changes. These increases are the primary drivers of climate change, contributing to 80% of the total radiative forcing from well-mixed greenhouse gases. The chapter details the dynamics of these gases, including their atmospheric budgets, natural and anthropogenic sources, and sinks. It discusses the role of oceans and terrestrial ecosystems in absorbing CO₂, the factors influencing CH₄ and N₂O emissions, and the feedback mechanisms between the atmosphere, land, and oceans. The chapter also assesses the projections of future changes in these biogeochemical cycles under different Representative Concentration Pathways (RCPs) and the potential impacts of carbon dioxide removal methods and solar radiation management on the carbon cycle. Key findings include: - CO₂ concentrations have increased by 40% since 1750, with fossil fuel combustion and land use changes being the primary drivers. - CH₄ concentrations have increased by 150%, driven by both natural and anthropogenic sources. - N₂O concentrations have increased by 20%, primarily due to agricultural activities. - Ocean uptake of anthropogenic CO₂ will continue under all RCPs, but the future evolution of land carbon uptake is less certain. - Climate change will partially offset increases in global land and ocean carbon sinks. - Nutrient limitations, particularly nitrogen, will limit the effect of rising atmospheric CO₂ on future land carbon sinks. - Ocean acidification and decreasing dissolved oxygen content are expected to continue in the future. - Irreversible long-term impacts of human-caused emissions, such as permafrost thawing, are likely to persist for centuries. The chapter emphasizes the need for comprehensive understanding and management of these biogeochemical cycles to mitigate climate change and its associated impacts.This chapter, authored by a team of international experts, provides a comprehensive overview of the biogeochemical cycles of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). It addresses the historical changes in these greenhouse gases, their sources and sinks, and their impacts on climate change. The chapter highlights that CO₂, CH₄, and N₂O have increased significantly since the pre-industrial era due to anthropogenic activities, particularly fossil fuel combustion and land use changes. These increases are the primary drivers of climate change, contributing to 80% of the total radiative forcing from well-mixed greenhouse gases. The chapter details the dynamics of these gases, including their atmospheric budgets, natural and anthropogenic sources, and sinks. It discusses the role of oceans and terrestrial ecosystems in absorbing CO₂, the factors influencing CH₄ and N₂O emissions, and the feedback mechanisms between the atmosphere, land, and oceans. The chapter also assesses the projections of future changes in these biogeochemical cycles under different Representative Concentration Pathways (RCPs) and the potential impacts of carbon dioxide removal methods and solar radiation management on the carbon cycle. Key findings include: - CO₂ concentrations have increased by 40% since 1750, with fossil fuel combustion and land use changes being the primary drivers. - CH₄ concentrations have increased by 150%, driven by both natural and anthropogenic sources. - N₂O concentrations have increased by 20%, primarily due to agricultural activities. - Ocean uptake of anthropogenic CO₂ will continue under all RCPs, but the future evolution of land carbon uptake is less certain. - Climate change will partially offset increases in global land and ocean carbon sinks. - Nutrient limitations, particularly nitrogen, will limit the effect of rising atmospheric CO₂ on future land carbon sinks. - Ocean acidification and decreasing dissolved oxygen content are expected to continue in the future. - Irreversible long-term impacts of human-caused emissions, such as permafrost thawing, are likely to persist for centuries. The chapter emphasizes the need for comprehensive understanding and management of these biogeochemical cycles to mitigate climate change and its associated impacts.