Along with major scientific organizations around the world, the Smithsonian book “Living in the Anthropocene” tells us that the global climate is warming because of greenhouse gas emissions from human activity. (Jim Lo Scalzo/European Pressphoto Agency/EFE)

The planet is becoming overpopulated — with humans, that is, not Javan rhinos or Sumatran tigers. And as never before, people are becoming urban dwellers.

By mid-century, two-thirds of the human race (by then almost 10 billion people) will live in cities and mega-cities.

John Kress, a veteran Smithsonian Institution scientist and curator of botany at the National Museum of Natural History, recalls that when he encountered the southeast Chinese community of Shenzhen decades ago, "it was a coastal village of 30,000 people and today has 15 million inhabitants. Fortunately, the Chinese are trying to make that a very green city."

Urbanization may be beneficial in ways that aren’t entirely clear to us today, but, undoubtedly, there will be downsides as well.

If you ask him, Kress is worried that as we become creatures of the city, we will further lose our touch with nature, which is about the last thing we need to happen.

HANDOUT IMAGE: Living in the Anthropocene, Earth in the Age of Humans, Foreword by Elizabeth Kolbert Edited by W. John Kress and Jeffrey K. Stine, Afterword by Edward O. Wilson Contribution by Thomas E. Lovejoy (Smithsonian Books/Penguin Random House)

A deep appreciation for a green world has nothing to do with sentimental or poetic reasons (which are entirely valid) but is necessary for us to feel the weakening pulse of the planet.

Kress is the co-editor of "Living in the Anthropocene," a new book by the Smithsonian that puts our current dynamic age in context through more than 30 essays by experts in disparate fields all affected by our changing planet.

The reader learns that the Earth is about 4.5 billion years old and that humans as we know them have been around for about 200,000 years. For the past 12,000 years, since the last great ice age, we have lived in the relatively calm climate of the geologic period we call the Holocene. But things started to change after the Industrial Revolution. We developed systems where progress was wrapped up with burning fossil fuels and generally treating the planet as something to be used, if not used up. Or as one of the essayists, the anthropologist Wade Davis, puts it: "The reduction of the world to a mechanism, with nature but an obstacle to overcome, a resource to be exploited, has in good measure determined the manner in which our cultural tradition has blindly interacted with the living plant." Perhaps the Age of Mammon might be a better term.

The book stems from Smithsonian symposia on the age of humans and adheres to the theory that the Holocene Age came to a wistful end around 1950, when a phenomenon known as the Great Acceleration began. Graphs show over the ensuing 60 years exponential increases in atmospheric carbon dioxide levels, fertilizer and water consumption, energy use and more. The number of people living in cities climbed from less than 1 billion to approximately 3.5 billion.

Although some peg the Anthropocene to the Industrial Revolution, circa 1780 to 1850, or earlier, the book's authors think the mid-20th century is a better date. Along with other major scientific organizations around the world, the Smithsonian tells us that the global climate is warming because of greenhouse gas emissions from human activity.

The book was at least 18 months in the works, but it has been published at an ominous moment, as three back-to-back extreme hurricanes — Harvey, Irma and Maria — swept across the Caribbean and the southern United States. Warmer ocean temperatures and more atmospheric moisture are seen as contributors to such violent storms, and climate scientists say we can expect to see more intense weather events than before.

The book also comes at a time when climate change and policy to address it, to put it kindly, are not the priorities of our leaders here in Washington. President Trump has decided to withdraw the United States from the Paris climate agreement, joining Syria and Nicaragua as non-signatories.

But the Anthropocene goes beyond just climate and weather and marks a period when we have altered the landscape for our needs, from building highways, expanding cities, converting forest and savanna to agricultural use, constructing dams and flooding river valleys, and all the rest. There is an environmental price for all this progress, in the loss of habitats, species and biodiversity.

“Personally, as a natural historian and a taxonomist, I’ve been traveling around the world my whole career, and I have seen these environmental changes happening,” Kress said. From Costa Rica to the American Midwest, he has seen habitats fragment into their own islands. “And we know from a lot of studies that islands hold fewer species,” he said.

All this is, admittedly, spirit sagging, but the last essays in the book see opportunities to move forward in the Anthropocene by conservation and habitat restoration, all predicated on a cooperative spirit between “citizens, governments, social and religious institutions, the marketplace, and the private sector.”

(If you want a calm, global perspective on all of this, set aside some time to read Pope Francis's encyclical on the environment.)

The eminent biologist E.O. Wilson offers the book’s afterword, in which he argues that we can save ourselves as a species only if we save other species, by large-scale habitat protection. If we get it right, “if we pass through safely and bring most of the rest of life with us, human existence could be a paradise compared to today.”

There is one thing most of us, even city slickers, can do to connect to nature, reduce our demands on the Earth and even produce some of our food, and that’s to plant and tend a garden, however small.

In the Anthropocene, we should hold sacred our urban parks, community gardens and green spaces and insist that our civic leaders do the same.

@adrian_higgins on Twitter