I consider myself a skeptical environmentalist, which is why I was really annoyed by the book by the same name by Bjørn Lomborg. The problem with Lomborg’s book was not the notion of reviewing the science behind the big environmental issues, but rather that he did such a poor job his treatment amounted to denialism, not skepticism. It as so bad, in fact, that Scientific American was motivated to dedicate an entire issue to systematically debunking his claims. This, of course, is part of a larger trend of tainting the word “skeptic” by using it to refer to science deniers and contrarions (and yes, there is a difference and denialism is a thing).

I am an environmentalist in the way that we should all be environmentalists – we should care about the biosphere in which we live. It is literally the only one we have. It is probable that human civilization will never have another, ever. Think about that. Interstellar travel will likely never be practical, and even if we can figure out a way to get to nearby systems, we will not find another Earth. Finding a world that is “earth-like” would require science-fiction level faster-than-light travel which may never be possible, and if it is will not happen anytime soon. Even then, there is a huge difference between “earth-like” and Earth. Terrforming other worlds in our solar system is also very difficult, and will take thousands of years if it is practical at all. So except for far future unpredictable scenarios – this is it. Our efforts are best spent preserving the world that is literally perfect for us, because we evolved here.

Beyond just surviving, I also love nature, perhaps more than the average person. Although people in general have an affinity for nature, and studies show that people are generally happier and healthier when they have exposure to nature. But as human civilization has grown, especially in the las century, we have displaced many natural ecosystems and impacted the environment in such a way as to stress many natural ecosystems. This is a serious issue because of, in a word, biodiversity.

Biodiversity specifically refers to the number of different species present in an ecosystem, and the amount of genetic diversity within those species. That latter point is critical, and often neglected. Frequently cuddly mammalian species are the poster child for extinction. However, even before a species goes extinct it can lose significant biodiversity within the species. This loss of diversity, statistically, can doom the species to near term extinction (over the next 100-1,000 years, say). So even when we successfully save remnants of species and prevent them from going entirely extinct, they still may be ultimately doomed because of critical loss of biodiversity.

The importance of biodiversity comes down to evolution. A robust species will likely be comprised of many distinct subpopulations, each evolutionarily tweaked to be adapted to a specific local environment. As environments shift, these subpopulations are a hedge against extinction because one or more of them may be better adapted to the new environment. Also, genetic diversity, even within subpopulations, is important to conferring resistance against infectious disease. Less genetic diversity makes a population more likely to be entirely wiped out by infection. Critical loss of biodiversity also leads to inbreeding, which can then lead to genetic disease.

Genetic diversity is something that slowly builds up within a species over thousands and even tens of thousands or hundreds of thousands of years. Spontaneous mutations happen over time, with the bad ones being weeded out by selective pressures, and some of the neutral or beneficial ones remaining. These mutations represent genetic diversity, but again, they accumulate very slowly. One “bottleneck” caused by a dramatic reduction in population can wipe out tens of thousands of years of accumulated genetic diversity. That is what we are causing right now – a genetic bottleneck in many species that may doom their long term prospects.

A recent BBC article summarizes recent studies looking at this issue. For example:

And this month, a report found global populations of mammals, birds, fish, amphibians and reptiles plunged by 68%, on average, between 1970 and 2016.

The report documents the dramatic reduction in biodiversity, which goes far beyond the loss of entire species. The biggest problem is habitat loss – only 25% of ice-free land on the Earth is still considered wilderness. The rest has been significantly altered by people, turned into farmland or living space, for example. A 68% loss of population within species over the last 46 years is a huge change over a short time. Where will we be in another 50 years, or 100? This, of course, is the blink of an eye when it comes to life on Earth, and even human civilization.

There is no one simple solution to this, and I am not advocating extreme measures to cripple our own civilization. What I would like to see is an international recognition of biodiversity loss as the serious threat that it is. One of the most important things we can do is limit further spread of human activity into the remaining natural ecosystems. This means, for example, no more cutting down forests to make more farmland. This also means limiting suburban sprawl. Making farming more efficient in terms of land use is a priority (which is my main beef with organic farming, which is 20% less efficient on average than technologically unlimited farming). We need to think carefully about how we are going to produce the calories and nutrition we need to live with the smallest footprint on this planet. And of course we need to move toward a technological infrastructure that minimizes pollution and environmental change or degradation.

We have to stop framing this issue as a culture war, or in terms of competition of different interests. We all have the same interest here, preserving the only environment suited to human thriving. And we need to approach this issue with science as the guide – not philosophy, not feel-good marketing, and not pseudoscience. We no longer have the luxury of indulging ourselves in such things.