Gaia’s Breath and Global Change

Abstract:

Aerosols and greenhouse gases play a significant role in the radiative forcing of Earth’s climate system. Aerosols cool the atmosphere by scattering light and forming clouds (i.e., direct and indirect radiative forcing of climate). Greenhouse gases, colored aerosols, and soot warm the atmosphere by absorbing infrared radiation. Cooling of Earth’s atmosphere by non-colored aerosol might offset warming by greenhouse gases, colored aerosol, and soot. Photooxidation processes are responsible for producing much of the fine aerosol in the global troposphere; however, the amounts are highly uncertain. Precursors to aerosol formation are generated from a myriad of sources including biogenic emissions of terpenes from vegetation, anthropogenic emissions of volatile and semivolatile hydrocarbons from urban areas, and agricultural emissions of ammonia (NH₃), amines, and nitrogen oxides (NO_x) from animal husbandry and cropping systems. The biosphere processes macronutrients (e.g., C, H₂O, N, P, and S) and generates aerosol precursors and greenhouse gases [e.g., carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O)]. Thus, the composition of the atmosphere and climate forcing are regulated by circulation of elements through the Earth system (i.e., the biogeochemical cycles of the elements), particularly by exchanges of chemical species between the atmosphere and the Earth’s surface. The presentation will discuss potential responses of the Earth system to the rate of nutrient supply, biospheric stressors like O₃ and temperature, changes in the succession of vegetation, and land use.