The Book - Chapters 9 to 11
In the last three chapters of our book Earth, Our Living Planet (Chapters 9 to 11), we explain large-scale feedback loops that largely control the Earth System, including the greenhouse effect and the level of atmospheric oxygen; the development of the Earth System over billions of years; and the effects of human societies, especially during the last, ongoing geological epoch called Anthropocene.
9-1. Regulation of the Earth System by Global Negative Feedbacks
Several long-term characteristics of the Earth System are regulated by large-scale feedbacks. In a feedback, a causal process [A] is amplified (positive feedback) or mitigated (negative feedback) by the response of another process [B] following the direct or indirect action of [A] on [B]. A feedback loop is created when the feedback-modified process [A] further influences process [B]. In Chapter 9 of Earth, Our Living Planet, we describe a number of Earth System's feedbacks and feedback loops that largely controlled the Earth System during its history, and continue to do it today.
Major negative feedback loops contribute to regulate key Earth System's characteristics at various timescales ranging from hundreds of years to tens of millions of years. We especially focus on three major characteristics of the Earth System – the greenhouse effect, the ocean's nitrogen-to-phosphorus ratio (whose value in the ocean is known as the Redfield ratio), and the level of atmospheric oxygen – and describe their long-term regulation by negative feedback loops.
Regulation of the nitrogen-to-phosphorus ratio in both seawater and phytoplankton biomass through negative feedback loops that involve nitrogen fixation in surface waters (grey) and the nitrogen cycle in the whole water column (black). Solid arrows: biological and chemical flows; dashed arrows: vertical transport of N-containing compounds.
9-2. Interactions Among Large-Scale Earth Processes
Effects (arrows) of forcing factors (left rectangles) and climate (right rectangles) on a number of large-scale processes of the Earth System (central rectangle). The forcing factors are tectonic, evolutionary and anthropogenic (black, grey and white rectangles and corresponding arrows, respectively).
In Chapter 9 of Earth, Our Living Planet, we also consider interactions between different types of components of the Earth System. We focus on the interaction between the global negative feedback loops that regulate environmental oxygen and solid oceanic carbonate, and between those regulating environmental oxygen and the oceanic nitrogen-to-phosphorus ratio. We also describe interactions of large-scale processes of the Earth System – such as global oxygen production and respiration – with the feedback loops.
In addition, we examine the responses of large-scale processes of the Earth System to geological, biological, and anthropogenic forcing factors, the climate and biological evolution. Human societies influence some of the large-scale processes of the Earth System. Contrary to biological evolution, which has influenced Earth System processes over tens to hundreds of millions of years, the current anthropogenic perturbations have timescales of at most a few hundred years but their effects may last thousands of years.
10-1. The Legend of the Eons – The Earth System Over Billions of Years
The global Earth System has been shaped by past and present conditions and events explained in Chapters 1 to 9 of Earth, Our Living Planet. We synthesize this information in Chapter 10 into a broad picture of the development of the Earth System over billions of years called The Legend of the Eons. This broad picture is used to describe the evolution of the Earth System, including recent effects of human societies.
In Chapter 10, we consider successively the following aspects of the Earth System: major external and internal abiotic processes that affect the Earth System; the acquisition by Earth of its physical properties, and their effects on the evolution of the planet; the main steps of biological evolution; the evolution of free oxygen in the Earth environment; and the emergence of negative feedback loops in the Earth System. We combine these aspects to describe the evolution of the Earth System, including effects of human societies.
The Legend of the Eons. The threads described in Chapters 1—9 of our book are woven here into a broad tapestry that depicts the progressive takeover of Earth by its organisms. Past time is to the left, and present time to the right. Vertical arrows: exchanges of materials between layers (for simplicity, these are only illustrated for the most ancient condition of the planet and the most recent). Patm: atmospheric pressure; T: temperature.
10-2. Effects of Human Activities Before the 21st Century
The period during which human societies had significant impacts on the Earth System is called the Anthropocene, which we also examine in Chapter 10 of Earth, Our Living Planet. We begin with distant events that occurred at the onset of the Anthropocene, such as the extinction of large indigenous fauna that often accompanied the occupation of new lands by Home sapiens, and we continue with the growth of the human population and the increasingly detrimental effects of human activities on the environment.
Three examples are discussed, showing how, during the second part of the 20th century, countries acted in concert to reduce or eliminate the causes of large-scale or global environmental disturbances. One of these examples is the ban on the insecticide DDT. These examples show that governments took action when scientific evidence and public pressure convinced them to do so. However, many other developing global environmental problems were not addressed in the 20th century despite mounting evidence they were building up.
Harmful effect of acid rain on a forest in the Jizera Mountains, Czech Republic, in 2006. Wikimedia.
Variations in the concentration of atmospheric carbon dioxide during the last 800,000 years. From NOAA.
11-1. Ongoing Effects of Human Activities – Adaptation and Mitigation
Human societies presently cause many perturbations to the Earth System, with potential long-term effects in the future. We explain in Chapter 11 of Earth, Our Living Planet the general mechanisms of climate change, ocean acidification, the loss of biodiversity, and water and food insecurity. We also examine the main human activities contributing to these four global perturbations, and their detrimental feedbacks into the environment and human activities.
Responses to the ongoing global anthropogenic perturbations include adaptation and mitigation. We explain how human societies can use adaptation to manage the unavoidable, and how they should use mitigation to avoid the unmanageable. We illustrate adaptation and mitigation using the example of ongoing and future sea level rise. The first and foremost mitigation action is to reduce the emissions of greenhouse gases by changing the manner in which human activities are conducted. With coordinated political will, this could be achieved within the next decades without altering the well-being of human societies.
11-2. Future Effects of Present Human Activities – Stewards of Planet Earth
Earth environments and human activities that are already or are expected to be impacted by global warming. PNGFuel .
The Earth System may be deeply modified beyond the 21st century by the ongoing human perturbations. We also look in Chapter 11 of Earth, Our Living Planet at four possible states of the future Earth System, which are: a long continuation of the present interglacial before the next glacial episode; a very long continuation of the present interglacial; the shift from the present icehouse Earth (long period with glaciers and/or ice sheets, as is the case since 34 million years) to a greenhouse Earth (long period without continental ice masses); and the crossing of planetary thresholds caused by a runaway warming, leading to a very different climate.
To illustrate the significance of some key biological innovations that shaped the Earth System, we consider what planet Earth would be without them. This leads to the idea that we should become the stewards of our unique planet without delay, taking into account the imperative need to preserve both its habitability and biodiversity.