The Race Between the Trees and the Light Bulbs

The Race Between the Trees and the Light Bulbs

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In the wake of the Paris climate agreement, I’ve been thinking about a riddle that has weighed on my mind for decades: Which are there more of in the world, trees or light bulbs?

A high school friend posed this question to me way back before the very first Earth Day, and we discussed it for hours on a tour of colleges we were making in New England. Think of the Amazon rainforest and all its trees! But what about New York City and all its lights? We went back and forth on the question, but we never felt confident we had a definite answer. For years afterward, we’d kid each other about “the race between the trees and the light bulbs.”

I half suspect that this seemingly unanswerable riddle played a role in setting me on my path to become an environmental writer. (My friend became a rheumatologist.) It’s relevant to the Paris agreement, in that we need trees to fare as well as possible in this race, since they produce negative emissions of carbon dioxide. Negative emissions can at least partly offset positive emissions, including those generated by light bulbs—both in their manufacture as well as in the vast majority of cases in which the bulbs are powered by carbon-based fuels.

One of the personal satisfactions of managing the Family Planning and Environmental Sustainability Assessment (FPESA) project at Worldwatch is that, through it, I’ve found an answer to the trees-and-light-bulbs competition. And the winner is:

There are more . . .

(Wait for it)

. . . trees in the world. A lot more. Thank God.

What makes me confident about this answer is that one of the many fascinating peer-reviewed scientific papers in our FPESA database, “Mapping Tree Density at a Global Scale,” calculates that there are slightly more than 3 trillion standing trees in the world. That works out—according to authors T.W. Crowther and colleagues—to well over 400 trees for each of the world’s 7.3 billion human inhabitants. (The mention of population was the reason this paper made it into our database, although the demographic analysis didn’t go far enough to rate an annotation in our upcoming report.) Yes, New York at night looks almost like a sunburst from an airplane, but it’s very unlikely that there are anywhere near 400 light bulbs for each one of us on the planet, especially given that 1.3 billion people lack access to electricity.

Despite this rare dose of good news, the authors also estimate that the world is losing a net of 10 billion trees each year—more than one rooted pillar of living carbon for each of us humans.

I was reminded of the “Mapping Tree Density” paper because the FPESA project wasn’t alone in noticing and appreciating it. Altmetric, a division of the London publishing technology start-up Digital Science, just released a list of the 100 “buzziest studies” of 2015—journal articles that generated the most news media stories and mentions in social media, blogs and Wikipedia. “Mapping” just missed the top 10, landing a ranking of 11, with 86 news media stories, 33 blogs, and nearly 1,000 tweets.

It’s an intriguing way to judge scientific papers, a fresh alternative to the “impact factor,” which evaluates a paper based mostly on how many other papers cite it. And the Altmetric list echoes FPESA’s interest in media impact, since papers that gain little attention in the news media and on the web are unlikely to inform public opinion, policymaking, or advocacy.

It was interesting to see that, as is the case with the FPESA database of papers, the authors of the buzziest studies were geographically diverse—from 105 different countries, publishing in 34 different journals. I’d be interested in how the Altmetric folks know where each author comes from. We haven’t figured out an easy methodology for that with our database. But we’re confident we’ve found a comparable diversity among the more than 900 papers we are assessing.

I was also gratified to see that three other papers—“Climate Change in the Fertile Crescent and Implications of the Recent Syrian Drought,” “Plastic Waste Inputs from Land into the Ocean,” and “Planetary Boundaries: Guiding Human Development on a Changing Planet”—were in both the Altmetric list and the FPESA database. Even more helpful, we were unfamiliar with two papers that made the Altmetric list but clearly qualify for our own as well, based on their treatment of both population and the environment. We added them to the database. More papers to read, assess, and maybe annotate!

You’ll be hearing much more from the FPESA project in 2016. Happy New Year, and let’s hope the trees keep winning the race against the light bulbs.


Robert Engelman is a senior fellow with the Worldwatch Institute and the director of the Family Planning and Environmental Sustainability Assessment (FPESA) project.

Banner photo by Alexander Kolosov.

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