Chapter Summary

It is well known that life depends on climate. That climate regulates the structure and functioning of terrestrial ecosystems is a foundational principle of geography and ecology. Anthropology shows, too, that climate was central in the development of human societies. We now know as well that life itself influences climate. Numerous biosphere–atmosphere feedbacks are evident at long paleoclimate timescales spanning tens of thousands and millions of years, but also at the shorter timescale of the past century. A physical and chemical understanding of climate has grown to a biological perspective that includes the biogeophysical and biogeochemical functioning of plants and terrestrial ecosystems. The chemical composition of the atmosphere and its temperature, water vapor, clouds, and heat transport are regulated in part by the biosphere. In addition, human societies, socioeconomic systems, and political systems have emerged over the past several centuries as dominant forces shaping the planet. To the physical, chemical, and biological understanding of climate is a new view that sees climate change over the coming centuries through a socioeconomic perspective and shaped by human actions. Life – the microbes and microorganisms in soil, the plants reaching skyward, and the people inhabiting the land – is a key factor that determines Earth's climate.

Ecosystems, Humans, and Climate Change

The notion that plants and terrestrial ecosystems affect climate and planetary habitability is embodied in the concept of coevolution of climate and life. Numerous books have explored this topic (Budyko 1974, 1986; Schneider and Mesirow 1976; Lovelock 1979, 1988; Schneider and Londer 1984; Schneider et al. 2004), and it is seen in the profound influence plants had on the geologic history of the planet (Beerling 2007). It is one part of an emerging recognition that a physical and chemical understanding of climate must expand to a biological perspective that includes the biogeophysical and biogeochemical functioning of plants and terrestrial ecosystems.

This view, as detailed in this book, arises from the multitude of anthropogenic perturbations in the Earth system and their multidisciplinary consequences. Carbon dioxide is a greenhouse gas that is central to understanding natural and anthropogenic climate change. It also alters leaf physiology and ecosystem functioning, and it inhibits isoprene emissions. Methane and N2O are important greenhouse gases, and they also affect atmospheric chemistry. Methane emissions can produce ozone and decrease the oxidizing capacity of the troposphere (OH radical) through NOx–VOC–O3 chemistry.