Blog: For Earth Week, guest speaker Gordon Bonan talks about environmental stewardship in the age of Earth system models

Graphic for Gordon Bonan talk

April 17, 2019

Editor’s note: Gordon Bonan, a researcher with the National Center for Atmospheric Research in Boulder, Colorado, is speaking at NAU as part of Earth Month. NAU News invited him to share more about his work in environmental stewardship. Hear the entirety of his speech at 4 p.m. April 22 at the International Pavilion.

In “The Invention of Nature—Alexander von Humboldt’s New World,” Andrea Wulf described the life and scholarly works of Alexander von Humboldt. Hailed by The New York Times as one of the 10 best books of 2015, Wulf portrayed Humboldt as a 19th-century visionary whose study of the natural world as a single interconnected system predated our modern understanding of Earth as a system. In his travels throughout the tropics, Humboldt developed a viewpoint in which, for example, tropical rainforests are essential to healthy planetary functioning and tropical deforestation alters climate. Meteorologists of Humboldt’s era parochially dismissed the notion that deforestation could affect climate. One leading meteorologist wrote that “rational climatology gives no basis for the much-talked-of influence upon the climate of a country produced by the growth or destruction of forests.”

Humboldt’s broad view of the Earth was largely forgotten over time, and the development of atmospheric science and ecology as academic fields of study followed disciplinary trajectories. The modern study of Earth as an interconnected system—the atmosphere, hydrosphere, geosphere, and biosphere—has only emerged in the last two decades as global models of Earth’s physical climate evolved into models of the Earth system.

The modern view of climate and global planetary change requires a broad view of the many physical, chemical and biological processes in the Earth system and how human intervention in these processes alters Earth system functioning. The study of planetary change is no longer simply about physical climate change but also about changes in land use (e.g., deforestation, reforestation, afforestation), biogeochemical cycles (e.g., carbon, reactive nitrogen) and biological feedbacks such as greening of the Arctic or browning from tree mortality that affect the trajectory of anthropogenic climate change. This science requires a new generation of scholars and intellectual leaders with a multidisciplinary perspective that integrates: atmospheric physics and dynamics; biogeochemical cycles, plant physiology and ecosystem functions; hydrology and soil physics; applied mathematics; and computational science.

This talk introduces Earth system models, how they are used to understand the connections between climate and ecology and how they provide insight to environmental stewardship for a healthy and sustainable planet. Global models of Earth’s climate have expanded beyond their geophysical heritage to include terrestrial ecosystems, biogeochemical cycles, vegetation dynamics and anthropogenic uses of the biosphere. Ecological forcings and feedbacks are now recognized as important for climate change simulation, and these models are becoming models of the entire Earth system. Two prominent examples discussed in the talk are anthropogenic land use and land-cover change and the global carbon cycle.

However, there is considerable uncertainty in how to represent ecological processes at the large spatial scale and long temporal scale of Earth system models. Further scientific advances are straining under the ever-growing burden of multidisciplinary breadth, countered by disciplinary chauvinism and the extensive conceptual gap among observationalists developing process knowledge at specific sites and global scale modelers. The theoretical basis for Earth system models, their development and verification and experimentation require a new generation of scientists who are adept at bridging the disparate fields of science and using a variety of research methodologies including theory, numerical modeling, observations and data analysis. The science requires a firm grasp of models, their theoretical foundations, their strengths and weaknesses and how to appropriately use them to test hypotheses of the atmosphere-biosphere system. It requires a reinvention of how we learn about and study nature.