We know that the Earth’s climate has changed in the past, including times when humans had yet to put in an appearance. These changes must, therefore, have been the result of ’natural processes’. So how do we know that current changes are not similarly natural? The challenge this poses for science is to understand the processes that were at work in the past, and compare them with the climate drivers, both natural and anthropogenic, at work today. There are two reasons to try to unravel the climatic history of our planet. The first might be described as its intrinsic interest. The more important reason is to see what lessons we can learn that might help us think about potential future climate change, and especially the much slower response of sea level to changes in temperature. This is the reason that it is now an important component of the IPCC process.

Planting trees for climate services – storing carbon, cooling surface climate, enhancing rainfall, providing aerosols that reflect solar radiation, creating favorable microclimate refuges, or other benefits – is not small-scale or immediate. It requires vast tracts of healthy and thriving forests and setting aside the land to grow forests for 50 to 100 years or longer. Achieving the climate benefits of forests requires a permanent forest presence over many decades. Climate will change during that time, and a forest planted today may not thrive in the climate of tomorrow. The forests of the future will grow in a climate different from today's and likely in regions of the world that differ from today's. They will be stressed by climate change, increased wildfires, disease, and insects. Asking forests to solve the climate problem requires a long-term commitment to and investment in forests and their health. Forest growth, too, is not one-directional. Wildfires, droughts, insects, and wind storms continually reset forests back to young stages of development. An old-growth forest that has accumulated enormous stores of carbon in its trees and soil becomes a young, regenerating forest.

Chapter 6 presents data about the first members of our own species, Homo sapiens, and how they lived and shared the planet with at least five other species of Homo. It presents the cultural succession of the Upper Paleolithic and the repercussions that our species had on the planet and other life forms as members spread out into virgin territories of the world.

Scott’s lifelong passion for trees is the subject of this chapter. Trees in Scotland’s folklore and mythology, as individual living species, and collectively in the environments that once were the nation’s great forests, are shown to be of paramount importance to his literary and personal writing. Articles for the Quarterly Review and other periodicals, letters to correspondents, including poet Joanna Baillie, and his unpublished personal planting journal Sylva Abbotsfordiensis are explored for their record of Scott’s nationally acknowledged expertise in silviculture, his planting programmes at Abbotsford and his experiments with growing conditions. Using a deep-time framework and recent scientific discovery, the chapter looks back to the first tree species to colonize Scotland after the last great glaciation. Scott’s planting of native species and advocacy of their value to the nation is revealed as a form of environmental reconstitution. Tensions between the aesthetics of planting and agrarian economics are investigated.

Expansion of the Human System began with divergence and migration of speaking communities in their homeland. Then, up to 45,000 years ago, migrants moved southwest across Africa and eastward along the Indian Ocean littoral, as documented through archaeology, genomics, and climate. Language evidence, supplemented by an accompanying website, confirms the value of Joseph H. Greenberg’s tradition of large-scale linguistic analysis. African migration included multiple settlements among preexisting hominin populations. The parallel migration into Asia, now identified genetically as a single migration, relied on watercraft at most stages. Surviving language groups indicate the path of migrants along the Indian Ocean littoral. Only after 45,000 years ago were migrants able to move northward, into the ecologically distinctive temperate zone. Once in the steppes, migrants moved east to Northeast Asia and west to the Black Sea. As networks facilitated exchange of dogs, religious ideas, bows and arrows, the Human System thus expanded from its initial locality to become a hemispheric network of communities in contact.

After millennia of cooling, the Last Glacial Maximum reached an extreme. Every species adjusted, even in the tropics. Humans responded with new social organization: communities pooled resources to face issues of leadership, forming confederations that pooled resources. After the coldest moment – 21,500 years ago – migrants moved to newly fertile lands as temperature rose almost ceaselessly for millennia. Intensive food gathering was accompanied by productive institutions: architecture for permanent homes, textiles, ceramics, and workshops for visual representation. Eurasiatic-speakers moved westward across Siberia; others moved both north and south in eastern Asia and between Africa and western Asia. New details on American settlement now reveal two groups of Asian voyagers who followed the “kelp highway” just offshore. The main group formed settlements along the Pacific littoral, expanding inland from points as far as southern Chile by 19,000 years ago. By the end of the Pleistocene, the achievements of early humanity included occupying most of Earth, supplementing foraging with production, exquisite visual representations, and dependable adaptability.