Climate Change: Are Humans Causing It?
What the evidence tells us
Climate change and global warming are subjects that stir up diverse opinions and heated arguments. However, this article aims to move beyond partisan debates and focus on scientific evidence to explore the role of human activity in climate change.
First, it's essential to understand that isolated weather events or anecdotal evidence don't provide a comprehensive picture of climate change. Instead, we must look at long-term trends and data to assess human impacts on the climate. Simplifying complex subjects is necessary for clarity and brevity, but this article strives to remain true to the scientific consensus.
Our core question is: Are humans significantly influencing the global climate?
The Greenhouse Effect
The key idea behind human-caused climate change is the greenhouse effect. Human activity is releasing large amounts of greenhouse gasses into the atmosphere that trap heat from the sun, leading to a rise in global temperatures and other effects that have a negative impact on human populations, other species, and Earth's ecosystem. The chief greenhouse gas is carbon dioxide (CO2), although methane (CH4) and nitrous oxide (N2O) play a role as well.
The Earth's temperature and atmospheric composition have fluctuated over its 4.5 billion-year history. Fossil records indicate periods of intense heat and periods of freezing temperatures. Barring cataclysmic events such as super volcanos and meteor impacts, this climate fluctuation has occurred over time scales on the order of tens of millions of years. Homo sapiens have only been around for about 200,000 years.
The Carbon Cycle
Earth's climate history, since the beginning of life, estimated at 3.5 billion years ago, has been heavily influenced by a system called the "carbon cycle." Humans, squirrels, trees, moss, bacteria, whales, and all life on Earth are based on and literally made of carbon. We are a carbon-based life form composed of various carbon-containing molecules. When living things die, their constituent molecules break apart and turn into other carbon-containing things through chemical reactions.
When a coyote is growing up, it eats rabbits. Through complex chemical reactions, some of the carbon in the rabbit becomes part of the carbon in the coyote, and some is exhaled in the process of respiration. When the coyote dies, it decays on the forest floor. Microbes like bacteria and fungi turn the coyote's carbon into other forms. Some ends up turning into CO2 gas that goes into the air. With the help of sunlight, that CO2 is then used by plants like trees and grass during photosynthesis for them to grow. Then a rabbit comes along and eats the grass and incorporates some of the carbon back into its body. Then a coyote comes along, eats the rabbit, and the carbon cycle continues. The same thing happens in the oceans, with some organisms absorbing carbon through photosynthesis and others releasing it.
Sometimes, when plants and animals die, their bodies end up in places like swamps, forest floors, or at the bottom of the oceans, where microbes can't fully decompose them and turn them into CO2. The organic matter can then get buried by sediment, which isolates its carbon. Over millions of years, the organic matter can become compressed and heated by geologic forces, permanently converting it to coal, oil, and natural gas, locking it away, and taking it out of the carbon cycle.
The carbon cycle is more complex than the above simplification, but the key point is that this effect of carbon being recycled throughout the ecosystem with some of it being buried underground has led to a remarkable state of homeostasis in the Earth's climate over the past tens of millions of years.
Industrial Revolution
In 1765 James Watt's improvement of the steam engine made it possible for the first time in history to convert heat to work at scale. This innovation sparked the Industrial Revolution. Before this, humanity could only accomplish work through manual labor or by using animals or water wheels. But being able to extract work from heat was a pivotal moment that would change the world. Coal was burned to heat water and turn it into steam that could be used to move trains or power industrial processes that were previously impossible. These steam engines could even be used to make electricity. After Thomas Edison invented the electric lightbulb in 1879 and George Westinghouse laid the foundation of the AC power grid, suddenly, there were thousands of uses for the coal-fired steam engine and its oil and gas-burning successors – electrically powered devices.
The ability to extract and burn these so-called fossil fuels unleashed untold productivity and prosperity. It did untold good for humanity in most areas. It significantly reduced the need for hard human labor (including slaves). It released the ox from the shackles of the plow. It spared the lives of whales whose fat was no longer burned to provide light. It created wealth and a standard of living that previous generations couldn't have even imagined. This wealth, however, did not come without consequence.
From a chemical perspective, these fossil fuels are hydrocarbons – molecules composed of hydrogen and carbon atoms. When they react with oxygen in a process called combustion (burning), they produce carbon dioxide gas, water vapor, and heat, and since combustion is never 100% complete, other various particulates that we collectively refer to as soot or smog. So when we burn fossil fuels we release huge quantities of carbon into the carbon cycle, in the form of atmospheric CO2, that has been locked up underground for millions of years.
The Earth maintains its life-supporting temperature by absorbing and reflecting a delicate balance of the energy from the sun. Infrared radiation can pass through Earth's atmosphere, where some gets absorbed by the land and oceans, and the rest gets reflected back into the atmosphere. Some of that infrared energy escapes back out into space, and some gets absorbed into the atmosphere by greenhouse gases. CO2 is a powerful greenhouse gas. That means it traps the sun's infrared energy in the atmosphere, contributing to a rise in temperature. This is the basic premise that the human-caused climate change hypothesis rests on.
But this leaves us with a few questions. Are we emitting more CO2? Is the atmospheric CO2 concentration abnormally high? Is the global average temperature actually rising? Fortunately, we have accurate data on this.
This graph shows that humans are indeed releasing a huge amount of CO2 into the atmosphere, and it coincides with the mass burning of fossil fuels.
This graph of the last 2000 years shows that human-caused CO2 emissions are causing a rapid and drastic rise in atmospheric CO2 concentrations. This spike correlates with the beginning of the Industrial Revolution when we began to burn fossil fuels at scale.
This graph of the last 800,000 years shows the cycles of peaks and troughs in CO2 concentrations. They track the cycles of ice ages (low CO2) and warmer interglacials (higher CO2). These periodic fluctuations are caused by changes in the Earth’s orbit around the sun – called Milankovitch cycles. CO2 concentrations did not exceed 300ppm throughout these cycles – today it is well over 400ppm.
This graph shows the global average temperature is rising. It has risen about 1.2°C (2.2°F) in the last 40 years.
Thinking solely in human terms, 1.2°C in 40 years doesn't seem like a lot. In fact, it's basically imperceptible to you and me. A 1.2°C temperature rise averaged across all the matter on Earth is an unfathomably large increase in total energy. We need to consider that nature consists of a delicate ecosystem where one process's output is another's input. Nature is full of feedback loops. Small changes can have enormous consequences that even the most sophisticated models cannot predict. This is called Chaos Theory, where minuscule changes in initial conditions lead to radically different outcomes over time.
So, humans do appear to be causing the Earth's climate to change. But what exactly will happen as a result? The short answer is we don't know for sure. This has never happened before. We must not assume that nothing bad will happen because nothing bad has happened yet. Although we don't know for sure what will happen, a few hypotheses are already proving to be correct and likely will continue.
The Effects
The one everyone has heard of is that the polar ice caps are melting at a high rate. This is a direct result of climate warming. Ice loss is catastrophic for the life that lives on it and under it. As the polar ice caps melt, the Earth's albedo (a measure of the Earth's ability to reflect the sun's energy) goes down (from 0.9 to 0.6), since white ice reflects more sunlight than dark blue water. This is a positive feedback loop where the more the ice melts, the faster it will melt.
Water freezing and forming sea ice at the Earth's poles causes the water to become saltier and denser. The denser water sinks, carrying oxygen, and disperses. This is what drives the currents for the world's oceans and provides oxygen to the depths. If the water stops freezing, the ocean currents and oxygen levels will be dramatically disrupted.
If an iceberg floating at sea melts, it does not change the water level at all (see Archimedes Principle). However, if ice sits on land where glaciers are melting, it will contribute to the sea level. One often overlooked effect is that the water expands as the ocean temperature rises. That has a significant effect on sea levels too. There are already signs of rising sea levels, causing coastal communities and cities to flood. Miami, for example, occasionally gets flooded from "king tides" that are caused by certain alignments of the sun and moon. From 1996 to 2018, the average sea level rose about 6 inches. That means king tides and storm surges will be 6 inches higher. That doesn't sound like a lot at first. But consider that sea level and the area flooded are non-linear. A king tide 2 feet above normal might flood 100 acres of the city, but at 2.5 feet, it might flood 500 acres, depending on the topography. A visualization of this effect can be found here. Rising sea levels could significantly devalue coastal real estate and potentially make it unusable. Average sea levels are projected to rise another 1-8 feet by 2100.
With more heat in the atmosphere, hurricanes have the potential to become a lot more intense. That's because warmer air holds more moisture and contains more energy, ultimately fueling hurricanes. Weather is a chaotic system and nobody knows for sure how it will respond to more heat in the atmosphere and oceans, but there is a high probability of increased storm activity.
Droughts in some areas are becoming more common and lasting longer, such as in the Southwestern US. Higher temperatures allow more moisture to be evaporated from the ground, drying out some areas. The moisture now in the atmosphere travels through wind currents to other areas. This effect can potentially cause more drought in arid regions and more rain and flooding in regions that already have water.
One negative feedback loop that stabilizes the rising atmospheric CO2 concentration is that the land and oceans will sequester carbon at faster rates as CO2 levels rise. Unfortunately, this effect can not completely offset the amount of CO2 being released by humans, and the remainder ends up in the atmosphere. This chart shows this effect.
A negative byproduct of the oceans absorbing more carbon is their pH levels falling, meaning they become more acidic. The acidification of oceans is leading to the bleaching and death of coral reefs – one of the largest sources of biodiversity on Earth. Diverse ecosystems are robust ecosystems. As biodiversity declines, so does resistance to attacks from invasive species, pests, and even viruses. If coral reefs die, the little fish that live there will either die or go somewhere else. Then the big fish that eat those little fish will either die or go somewhere else, and so on down the food chain. The people whose livelihoods depend on the sea for fishing or collecting shellfish will be impacted too. Coral reefs help stabilize coastlines. If the coral dies, coastal lands are likely to be eroded.
Another concern is that if the Earth's temperature rises sufficiently to melt the permafrost in the arctic tundra, a massive amount of methane and CO2 will be released into the atmosphere all at once. This would be a non-linear event, as methane is 25-35 times as potent as carbon dioxide, and there's a whole lot of it frozen in that permafrost. Once all that methane and CO2 is released, warming will likely accelerate at a non-linear rate.
Conclusions
So the answer appears to be, yes. It's evident that humans are indeed changing the Earth's climate by releasing huge quantities of carbon dioxide into the environment that has been locked away deep below the surface for millions of years, dramatically altering the equilibrium of the carbon cycle. The extent of the effects of climate change are not and cannot be known with precision. However, it will likely negatively impact humanity and countless other ecosystems on Earth.
My biggest concern is what we cannot predict. The ecosystems of the Earth are delicate, complex, and governed by chaos. They are extremely sensitive to initial conditions. They behave unpredictably despite their seeming simplicity and the fact that the forces involved are governed by well-understood physical laws. A few degrees of temperature rise or changing rainfall patterns may seem trivial on the surface if that were the only thing that changed. We are likely blind to the trouble that lies several steps down the chain reaction of this Rube Goldberg machine we call life. Add the extremely high latency of observation time (since Earth's systems are like a gigantic flywheel that takes a while to react to the effects of high carbon dioxide levels), and the potential is there for climate change to have significant effects.
To say for sure that human-caused climate change is going to make us all die soon or to say that it's completely fake are two viewpoints of the uneducated and ignorant. We know that human-caused climate change is happening; it's probably not good, but we don't know how bad it will be.
I am forever grateful that fossil fuels were discovered and that they were burned to provide the energy to create innovations and wealth we all enjoy. We didn't understand the negative effects of doing so because it led to prosperity in the moment and externalities later. If we continue emitting huge quantities of CO2 by burning fossil fuels at the current rate, we might have a problem. We have reason for optimism, though, since innovations are leading to more efficient uses of resources, dematerialization, and low or no CO2-emitting energy sources. The key is not to be complacent.
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