Earth Day and What Science Can Teach Us

Today is Earth Day. So what do we know about Earth? Terra, to give Earth its Latin name, is the third planet out from Sol (aka the Sun), a medium sized yellow star in an outer spiral arm of the Milky Way galaxy. Earth is a rocky planet of 12, 756 km in diameter and it orbits 150 million kilometers from the Sun. It is approximately 4.6 billion years old and has a single, relatively large satellite named Luna (aka the Moon). The present atmosphere of Earth is about 78% nitrogen, 21% oxygen and 1% water vapor and other gases. The most notable feature of Earth is that it is home to a huge variety of life that has dramatically shaped its physical features. Life appeared very early in Earth’s history, perhaps as early as half a billion years after the planet’s formation. However, it took several billion more years for multicellular life to appear and evolve into more complex forms, with one of the most recent to appear (only a few hundred thousand years ago for the present species) being a type of ape that in the last few millennia has developed an agricultural civilization and in the last couple of centuries has seen explosive population growth and rapid advances in technology. I refer, of course, to our own species, Homo sapiens, i.e., humans.

Virtually all the information in the previous paragraph is well established fact, and all of it we know due to science. In the last couple of centuries, our understanding of the planet we live on and its place in the universe, as well as the history of our own species, has advanced hugely due to science. Science is distinct from belief systems such as religions, as it is based on observation, evidence and analysis. That isn’t to say that science (or more accurately, scientists, who after all are only human) never gets things wrong, much less that it has answers to everything. But over time, science has given us a very good, if still incomplete, understanding of many aspects of reality, and since it is firmly based on logic and evidence, it is far more reliable than any other way of explaining things.

The above may seem self-explanatory to most knowledgeable people, but it is still necessary to emphasize it, because not only is there still a very large segment of humanity who doesn’t accept significant portions of our scientific understanding of the world, but the US government itself has largely fallen under the control of people with an anti-science attitude. This is why Marches for Science have been organized for today around the US and the world, because despite the self-evident benefits that science brings to humanity and the obvious advantages of having a more accurate, science-based understanding of the world around us, there are many people in power (and ordinary people who support those people) who deny scientific explanations of reality.

Climate change is just one example of an issue where this anti-science attitude has caused and continues to cause great damage, but as it is the most important and urgent, it is worth special attention. In fact, it isn’t necessary to be a scientist or have a detailed knowledge of climatology to understand the basics of climate change. Simply put, certain gases in our atmosphere trap heat, causing Earth’s atmosphere to act as a blanket that raises the planet’s surface temperature. Essentially, the atmosphere is transparent to visible light, the form which most of the energy Earth gets from the Sun takes, but the Earth radiates most of the energy back in the infrared, i.e., as heat, and like the glass in a greenhouse, these gases – naturally referred to as greenhouse gases – are opaque to infrared radiation, so they trap the heat, making the planet’s surface hotter. This is not a bad thing, as without this greenhouse effect Earth would be much colder, certainly too cold for human life. But too much of a greenhouse effect is not a good thing either, as the example of Venus illustrates. Venus is physically very similar to Earth, but due to a runaway greenhouse effect it has an extremely thick atmosphere primarily consisting of carbon dioxide and surface temperatures of over 450 degrees Celsius, far higher than temperatures on Mercury, even though the latter is closer to the Sun. The chief greenhouse gases in Earth’s atmosphere are water vapor, carbon dioxide and methane (the gases that make up most of the atmosphere, nitrogen and oxygen, are not greenhouse gases). Of the three main greenhouse gases, water is the least efficient at trapping heat while methane is the most efficient, but because water is by far the most plentiful, it contributes the most to the greenhouse effect, followed by carbon dioxide. Methane does contribute substantially, despite only being present in trace amounts, though unlike the other two gases it breaks down into its component elements relatively quickly, so it doesn’t accumulate as easily.

So we know that carbon dioxide and methane are greenhouse gases. This is a fact that has been known to science for a very long time and is clearly demonstrable experimentally. Furthermore, these two gases are major contributors to the greenhouse effect. This is also well established. We also know that human industrial activity, mostly involving the burning of fossil fuels such as coal and oil, produces large amounts of carbon dioxide, and that other types of human activity, such as livestock raising and leaks from natural gas (i.e., methane) production results in the release of methane. What’s more, we know that the amount of carbon dioxide in Earth’s atmosphere has gone from around 270 or 280 ppm (parts per million) in pre-industrial times to around 400 ppm today, a very substantial increase. Finally, we know that average global temperatures have increased by a significant amount over the past century, with a particularly rapid increase over the last few decades. Though some try to question this latter fact, they can only do so through cherry-picking of data, and even that has become pretty hard to manage as the data showing warming becomes more overwhelming.

To repeat, we know the following facts:
1. Carbon dioxide is a greenhouse gas that contributes significantly to the greenhouse effect, as is methane
2. Human industrial activity produces large amounts of carbon dioxide and significant amounts of methane
3. The amount of carbon dioxide in the atmosphere has increased from less than 300 ppm in pre-industrial times to about 400 ppm now
4. Average global temperatures have also increased significantly over the same period, particularly in recent decades.
The conclusion is obvious. Human activity is warming the planet at a rapid rate. While an increase of 1 degree Celsius or so, which is approximately how much warmer the last couple of record-breaking years have been over the 20th century average, may not seem like much, it is actually a very large amount, as changes of just a few degrees can make the difference between an ice age in one direction and the melting of the polar ice caps in the other. This is why we have to take climate change seriously and do so now.

Those who want to challenge this obvious conclusion attack the science in different ways. One is to emphasize the uncertainties. Of course there are always some uncertainties; in a sense, science is all about uncertainties, as it involves trying to find answers to all the things we don’t yet know. What’s more, good scientists always acknowledge the uncertainties that exist, because claiming to be sure when the evidence doesn’t support it is bad science. So, for example, there is still some uncertainty about the exact ratios of the three main greenhouse gases’ contributions to the greenhouse effect. But that doesn’t change the fact that carbon dioxide and methane are both major greenhouse gases. Some cite the fact that we still can’t predict the weather with a high degree of certainty to cast doubt on climate models. But in fact it’s easier to identify long-term climatic trends than to predict day-to-day variations in chaotic weather systems. Some talk about how “the climate is always changing” or how there have been times in Earth’s past where the planet has warmed and carbon dioxide levels increased without humans being present. This ignores the obvious points that just because the climate has changed for reasons other than human action in the past doesn’t mean the current changes aren’t caused by humans, any more than the fact that forest fires happened before there were people means that humans never cause forest fires, and that very slow, gradual change is one thing, rapid change that is too fast for us or individual ecosystems to adapt to is something else entirely.

Then there’s the frequently repeated claim that a few decades ago scientists were talking about global cooling and that they only recently started talking about global warming. This one is just plain false. As far back as the 19th century it was pointed out that human burning of fossil fuels could lead to an increase in global temperatures, and more than half a century ago this was widely acknowledged among scientists. The media stories in the late 1970s about the possibility of an impending ice age did not represent a widely held consensus among scientists, and in fact the very idea was prompted in part by the well understood fact that in the absence of other factors human production of carbon dioxide would cause temperatures to rise. Temperatures had risen slowly but steadily for most of the first half of the 20th century, but they stopped increasing for a few decades after that. So one suggestion, if not a widely accepted one, was that a natural cooling trend was counteracting the human effects on temperatures, and if it continued it might lead to an ice age. But there were other explanations, such as that other pollutants, such as those that made up the smog so commonly seen in industrial nations in the 1960s and 1970s, were blocking sunlight and balancing out the effects of carbon dioxide and methane production. This latter explanation seems more likely, though I don’t know if it is the one most climatologists accept today. In any case, the warming trend started up again by the 1980s and is now proceeding at an unprecedented pace, so whatever the explanation for the pause in the warming trend in those decades, the planet is clearly not cooling.

Of course science tells us many other things that we need to pay attention to, such as the effects of human activity on ecological systems (e.g. through overfishing, elimination of predators, introduction of invasive species, and so forth), the effects of chemicals and other substances we produce on human health (e.g. pesticides, chemicals in food and other products we use daily, and lead and other pollutants in our environment), the effects of overuse of antibiotics on the spread of diseases, and much more. Again, some people may want to deny what science can tell us on these issues due to ulterior motives, while many others simply prefer to ignore it because that’s easier than doing something about the problems. But we ignore science at our peril, as the long-term consequences of letting these problems fester are sure to be much worse than the difficulties of tackling them now.

But coming back to the planet that we celebrate on Earth Day, science tells us more things about it. One is that Earth itself is in little danger from anything we may do. The planet will be here for billions of years more, whether humanity survives or not. Another is that life on Earth is almost sure to survive in some form even if we drastically alter the environment for the worse. Life on Earth is pervasive and appears even in the most seemingly inhospitable environments. Unless we somehow set off a runaway greenhouse effect like that that transformed Venus into the place it is today, some life will survive the worst we can do. Life on Earth has been through a number of mass extinctions like the one that killed off the dinosaurs (and most other species on Earth at the time) and has always rebounded; at worst humanity will just be the first species to cause a mass extinction of other species on its own. Even the global warming we cause won’t be permanent, as the carbon cycle will eventually result in the excess carbon dioxide getting absorbed into limestone (though as this takes thousands of years, our transformation of the environment can easily destroy our civilization and wipe out many other species in the meantime). But if we as a species want to survive, and if we want to maintain our present day civilization, we’d best heed what we can learn from science.