Chapter Summary

Geoengineering is the purposeful intervention in climate through various methods and technologies applied at a scale sufficiently large enough to alter regional or global climate. Such approaches are broadly grouped into solar radiation management and CO2 removal and on land include: increasing the albedo of the land surface; agricultural management to reduce greenhouse gas emissions; large-scale afforestation and reforestation to enhance the terrestrial carbon sink; and use of biofuels to reduce anthropogenic CO2 emissions. In cities, building design practices such as white roofs and green roofs provide a means to lessen the urban heat island. Managing terrestrial ecosystems for CO2 removal has received much scientific study, but biogeophysical climate consequences (chiefly through albedo and evapotranspiration) must be considered in addition to the biogeochemical benefits. Future land-use choices have varying biogeophysical and biogeochemical outcomes for climate over the twenty-first century, and in some cases these counteract one another. Land-use choices additionally alter the cycling of reactive nitrogen in the Earth system, emissions of mineral dust and biomass burning aerosols, and emissions of biogenic volatile organic compounds, each of which has significant chemistry–climate feedbacks. The climate consequences of land use must be studied in an integrative, interdisciplinary framework to prevent unintended outcomes of climate intervention policies. Moreover, many biogenic emissions affect air quality, and air pollution control and climate change must be treated in a common policy framework. To balance the climate and socioeconomic outcomes of land use, Earth system models are beginning to include socioeconomic decision making.

Adaptation, Mitigation, and Geoengineering

A changing climate has various impacts on human systems including food availability, water resources, health and disease, and socioeconomic stability, as well as disrupting the functioning of natural systems. Many approaches are available to respond to the environmental and socioeconomic challenges posed by anthropogenic climate change. In scientific parlance, adaptation is the adjustment to climate change (Allwood et al. 2014). In the context of human systems, adaptation refers to intervention to moderate or avoid harmful effects or to exploit beneficial outcomes of climate change. Mitigation describes human intervention to reduce the sources or enhance the sinks of greenhouse gases or to reduce the emissions of other substances that contribute to climate change (Allwood et al. 2014).