In one of his most influential and important works, The Practice of the Wild (1990), Gary Snyder reminds us of the conditional nature of life on earth. As he put it:  Two conditions – gravity and a livable temperature range between freezing and boiling – have given us fluids and flesh. Thankfully, our planet is in just the right orbital around the sun, massive enough to hold an atmosphere, a stable tilt providing predictable seasons, a molten core that recycles carbon, and a magnetic field that protects us from the solar wind. In a relatively short time of stability, humans have evolved. Snyder points out that fingers and toes, eyes and ears, even our wagging tongues owe something to our evolution as land-striders, tree climbers and weather-watchers.

Something in Snyder’s earth sense was brought to mind while reading this brand new book by Ruth DeFries, The Big Ratchet – How Humanity Thrives in theFace of Natural Crisis (Basic Books, 2014). While not a poet, DeFries shares a perspective with Snyder that comes from careful observation and deep reflection. As a geographer and environmental scientist, she’s taken a different road to understanding earth systems and human systems, but her conclusions are similar to the Buddhist poet.

To be sure, this is a short, easy-reading book with a conversational tone. The language is straightforward and approachable, offering a clear narrative interlacing stories of technical innovations with the exponential growth of human populations. What makes us different from other species, DeFries says, is not our ability to manipulate our surroundings; rather, we have developed and extraordinary ability to twist food from nature. Our ability to pass knowledge across generations has given us a remarkable capacity to try, fail and adapt. If one experiment fails, we lurch, stumble, and try some other path.

And that is a key focus of the book, how human populations and societies have grown or ratcheted up to the limits of food production, suffered starvation and other loss (i.e., the hatchet), but somehow managed to discover or unearth a solution (i.e., pivot). For example, DeFries reminds us that natural limits to bio-available nitrogen once greatly limited food production. By the nineteenth century, expanding urban populations were facing food shortages as all the supplies of recycled wastes and imported guano failed to keep pace with demand. Then, German chemist Fritz Haber came along to add a spark to humanity’s accumulated knowledge and show how electricity could be used to fix nitrogen from the air producing ammonia fertilizer. Cleverly joining invention, innovation with accumulated knowledge, human kind has continued to prosper and grow at an exponential rate.

This is a hopeful story, a hopeful book – within limits. DeFries clearly states that: there are three fundamental requirements needed for a habitable planet: a stable climate, a planetary recycling apparatus and a smorgasbord of life. As she points out, there are limits to planet’s support system and the massive increase in population and food demand over the last 60 years or so strikes at these fundamental requirements. An increasingly unstable climate threatens to disrupt food production across the globe. Unpredictable planting seasons, drought, heat waves and storms are worldwide climatic changes that threaten food supplies everywhere. We greatly complicate matters by disrupting the recycling of nutrients, discharging them as sewage to rivers  and oceans and into the air.

Still, DeFries takes a long view and sees reason for hope. In the final chapter of her book, she says that human ingenuity is once again leading to positive change. While acknowledging the impacts of exponential population growth, she says the end of the demographic upheaval is in sight. She also sees humanity beginning to pivot away from wasteful business-as-usual, finding new ways to recycle nutrients, re-localize food production, reduce food wastes, and adopt healthier diets.

However, she leaves us with caution. After the big ratchet up of population over the last century, we face a time of great change and global challenges. She says we are learning that urban lives are connected with nature only against strong headwinds driven by the push to consume more. All of us, she says, need to do much more to keep the hatchets from falling too severely.