Feedbacks in the Earth System

Abstract

This book investigates the billion-year takeover of planet Earth by its organisms and ecosystems. This chapter considers feedbacks and feedback loops that deeply affected the Earth System at some crucial steps of its long history, and continue to affect it today. It explains the different effects of positive and negative feedback loops on the Earth System, which cause runaway effects or promote a settling to equilibrium or self-regulation, respectively. Two negative feedback loops, which involve the oceanic carbonate system and the chemical alteration of silicate rocks, respectively, have generally prevented the occurrence of runaway cooling or warming of the planet. The Chapter examines in detail three major characteristics of the Earth System—the greenhouse effect, the ocean’s nitrogen-to-phosphorus ratio (whose actual value in the ocean is known as the Redfield ratio), and the level of atmospheric oxygen—and describes how major negative feedback loops contribute to regulate these characteristics at various timescales ranging from hundreds of years to tens of millions of years. For example, the history of free oxygen (O₂) on Earth began with the emergence of O₂-photosynthetic organisms, and largely determined the course of the Earth System over more than 2.4 billion years. The chapter further considers interactions between different types of components of the Earth System, and especially interactions between the feedback loops that regulate environmental O₂ and solid oceanic carbonate, and environmental O₂ and the oceanic nitrogen-to-phosphorus ratio. It also examines the responses of large-scale processes of the Earth System to geological, biological, and anthropogenic forcing factors, the climate and biological evolution.

Figure Credits

Fig. 9.1 Original. Figure 9.1 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla

Fig. 9.2a Original. Figure plotted using the numerical data from page 8 of Johan Mathieu (2017). Figure 9.2a is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla.

Fig. 9.2b Original. Figure 9.2b is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla.

Fig. 9.3 Original. Figure 9.3 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla.

Fig. 9.4 Original. Figure 9.4 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla.

Fig. 9.5 https://commons.wikimedia.org/wiki/File:Global_Carbon_Emissions.svg by Autopilot https://en.wikipedia.org/wiki/User:Autopilot?rdfrom=commons:User:Autopilot, used under CC BY-SA 3.0, CC BY-SA 2.5, CC BY-SA 2.0, CC BY-SA 1.0 and GNU FDL FDL. Line styles of the six lines changed, and title of Y-axis modified.

Fig. 9.6a,b Original. Figure 9.6a,b is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla.

Fig. 9.7 Original. Figure 9.7 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla.

Fig. 9.8a https://www.climate.gov/sites/default/files/paleo_CO2_2018_1500.gif, from https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide by NOAA, in the public domain. Some indications inside the figure removed, numbers on the X-axis changed, and titles of the two axes rewritten

Fig. 9.8b This work, Figure 9.8b is a derivative of https://en.wikipedia.org/wiki/File:Phanerozoic_Carbon_Dioxide.png by Robert A. Rohde https://en.wikipedia.org/wiki/User:Dragons_flight, used under GNU FDL and CC BY-SA 3.0. Figure 9.8b is licensed under GNU FDL and CC BY-SA 3.0 by Mohamed Khamla

Fig. 9.9 This work, Figure 9.9 is a derivative of https://commons.wikimedia.org/wiki/File:Solubility-co2-water.png by The Engineering Toolbox (multiple authors), https://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html, in the public domain. I, Mohamed Khamla, release this work in the public domain

Fig. 9.10 Adapted from Fig. 1a of Gruber and Deutsch (2014). With permission from Prof. Nicolas Gruber, ETH Zürich, Switzerland

Fig. 9.11a https://commons.wikimedia.org/wiki/File:WOA09_sea-surf_NO3_AYool.png by Plumbago https://en.wikipedia.org/wiki/User:Plumbago, used under CC BY-SA 3.0

Fig. 9.11b https://commons.wikimedia.org/wiki/File:WOA09_sea-surf_PO4_AYool.png by Plumbago https://en.wikipedia.org/wiki/User:Plumbago, used under CC BY-SA 3.0

Fig. 9.12 This work, Figure 9.12, is a derivative of https://commons.wikimedia.org/wiki/File:F_ratio_diagram.gif by Plumbago at English Wikipedia https://en.wikipedia.org/wiki/User:Plumbago, used under GNU FDL and CC BY-SA 3.0. Figure 9.12 is licensed under GNU FDL and CC BY-SA 3.0 by Mohamed Khamla

Fig. 9.13 This work, Figure 9.13, is a derivative of https://commons.wikimedia.org/wiki/File:WOA09_180E_AOU_AYool.png by Plumbago https://en.wikipedia.org/wiki/User:Plumbago, used under CC BY-SA 3.0. Figure 9.13 is licensed under CC BY-SA 3.0 by Mohamed Khamla

Fig. 9.14 Figure of Breitburg et al. (2018). With permission from Prof. Denise Breitburg, Smithsonian Environmental Research Center, USA

Fig. 9.15 Modified after https://earthobservatory.nasa.gov/images/4097/global-chlorophyll by NASA earth observatory, https://eoimages.gsfc.nasa.gov/images/imagerecords/4000/4097/S19972442003273_lrg.jpg, in the public domain

Fig. 9.16 Original. Figure 9.16 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla

Fig. 9.17 Original. Figure 9.17 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla

Fig. 9.18 Modified from Fig. 1 of Jaccard et al. (2014). With permissions from Prof. Samuel L. Jaccard a University of Bern, Switzerland, and The Oceanographic Society under its CC BY 4.0

Fig. 9.19 Original. Figure 9.19 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla

Fig. 9.20 Original. Figure 9.20 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla

Fig. 9.21 Original. Figure 9.21 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla

Fig. 9.22 Original. Figure 9.22 is licensed under CC BY-SA 4.0 by Philippe Bertrand, Louis Legendre and Mohamed Khamla