An introduction to man-made climate change

By now we’re all pretty familiar with the fundamentals of climate change — why it’s happening and how. Still, there’s a lot of misinformation floating around on the subject. Most of it dismisses climate change from the get-go, while some sources call into question the validity of our data or our role in driving the process.

Image credits Paul Brennan.

Some of these allegations are based on a kernel of truth but are then twisted so far from their roots that they lose all practical meaning (for example, that climate can change due to natural causes).

Today, I’d like to take a stab at explaining the mechanisms that shape climate, their interplay, and how we fit in the whole picture.

Natural Climate Change

Our planet’s climate patterns do show a degree of natural variability. Climate is the product of many different factors. Non-biological ones include volcanic activity, the distribution and strength of ocean currents, changes in the planet’s orbit, or fluctuations in solar output.

Volcanoes primarily work to cool the climate overall through eruptions. During such an event, clouds of smoke and ash blanket large areas of land, reducing incoming energy from the sun; these usually deposit on the surface within three months. A more long-lasting agent of cooling in the case of volcanoes is sulfur dioxide. It reacts with water vapor in the atmosphere, creating sulfate aerosols that reflect sunlight back into space for a year or longer. While eruptions do release CO2, which acts as a greenhouse gas, their cooling effect far outweighs it — for example, the eruption of Mount Pinatubo in 1991 caused a 0.5 °C drop in average global temperatures for several years.

An explosive eruption.
Image via Wikimedia.

Ocean currents move heat around the planet, helping to homogenize temperatures and having a profound effect on climate patterns. They move warm water from the equator towards the poles.

Shifts in the Earth’s orbit can have immense effects on climate, potentially starting and ending ice ages. While definitely powerful, they’re also slow, and their effect on climate is only noticeable over thousands of years. Changes in the tilt of the planet (relative to the perpendicular plane of its orbit, currently at 23.5°) affect the strength of different seasons. More tilt makes for warmer winters and colder summers, while less tilt makes all seasons milder and more similar.

Since the Sun is ultimately the source of most energy on Earth, any variations in its output will have dramatic effects on the climate of our planet. Although you couldn’t tell from day to day, our star’s output does vary over time. For example, a decrease in solar activity is believed to have led to the Little Ice Age between the 15th and 19th centuries.

Although powerful, these changes happen slowly. It takes thousands of years for the Earth’s orbit or its currents to naturally shift, and the Sun is similarly slow-paced. Volcanic eruptions are blisteringly fast by comparison, but their effects are much less dramatic and shorter-lived.

Where life comes into the picture

Image via Pixabay.

Life can only sustain itself by changing the environment. Even the humblest microbe in the pool needs to break down and alter the chemical compounds it has access to in order to generate energy and survive. Pollution, then, is part and parcel of being alive.

This pollution can have a huge impact on the planet and everything living on it. Around 2.4 billion years ago, cyanobacteria (bacteria that can photosynthesize) began polluting the Earth with oxygen in an event known as the Great Oxygenation. It set the stage for oxygen-breathing, complex life to form, but for the other microorganisms living at the time, it caused wide-spread extinction. Whole ecological niches were opened up by this highly-reactive gas, allowing cyanobacteria to eventually evolve into multicellular life.

The red and green lines are our upper and lower estimates of atmospheric O2 throughout the Earth’s history (in billions of years, Ga). 0.2 corresponds to 20% by volume.
Image credits Heinrich D. Holland, (2006), Phil. Trans. R. Soc. B.

Another snapshot of history that showcases how biology and climate interact is the Carboniferous, a geologic period that spanned between 360 and 300 million years ago. What set apart this time period from any other is that woody trees were becoming wide-spread, sea levels were decreasing so fresh, marshy lands were exposed, and there weren’t any microorganisms around who knew how to decompose the lignin in wood yet. Atmospheric oxygen levels rose while CO2 concentrations plummeted. Average temperatures at the start of the period were high, around 20 °C (68 °F), but by the Middle Carboniferous they dropped to around 12 °C (54 °F) — a change of 8 °C in around 30 million years.

All things considered, biological activity can influence climate much more quickly than non-biotic factors. However, its effects tend to be directly proportional to the size and diversity of the biosphere and are less dramatic upfront but compound over time. Finally, biological factors tend to maintain a set of conditions that support life in its current form (the Gaia principle). Plants and animals, for example, use one another’s pollution (O2 and CO2) as fuel, keeping their concentrations and effect on climate in check.

Man-made climate change

Image credits Ralf Vetterle.

What humanity has that no other species can even come close to is sheer scope and speed.

We are the dominant lifeform on Earth, and our reach is so long that we’re becoming one of the main forces shaping the evolution of the entire planet. No other species or group of species transforms and consumes more of the environment than we do. Very, very few natural forces match us for scope, and virtually none can rival us for speed of action. While we’ve always had an effect on climate, it became problematic after the Industrial Revolution of the 19th century with few exceptions (which is why it’s used as a reference point in discussions on climate change).

What we’re seeing today is that average temperatures have increased by 0.9 °C (1.62 °F) since the beginning of the 19th century. That rate of change is 3,750,000 times faster than the one in the Carboniferous. Unlike what occurred during the Carboniferous, however, average temperatures are now going up. The past five years are the warmest on record, and they’re the worst offenders in a long range of successive ‘hottest years’ since the 1970s.

This trend has been predicted ever since the 1860s, when Irish physicist John Tyndall published On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connexion of Radiation, Absorption, and Conduction, a paper that set the foundation of climate science today. Tyndall was the first to show that gases in the atmosphere absorb and retain heat to different degrees — with carbon dioxide being a main offender. By 1896, Svante Arrhenius built on his work to show that increased levels of atmospheric water vapor and CO2 will drive up average ground-level temperatures (On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground). The link between CO2, other greenhouse gases, and climate change is that these compounds prevent heat on the surface of the Earth from reflecting back to space.

Today, CO2 levels in the atmosphere are the highest they’ve ever been during the last 3 million years, breaking the 415 ppm (parts per million) mark last May. Just like average temperatures, they’ve been steadily climbing.

Two factors are contributing to this rise: higher emissions from our day-to-day activities and massive environmental degradation. We’re putting in a record amount of carbon dioxide into the atmosphere — around 37 billion tons of the stuff per year — while reducing the ability of natural systems to remove it.

Roughly 10% of all annual human greenhouse gas emissions (GHG) are caused by deforestation. That land is then given over to be used for crops (agriculture generates between 10% and 11% of all human GHG annually), industry (24% of human GHG annually), infrastructure (transport generated 23% of global GHG in 2010), or residential areas (which also generate GHG through the energy they consume).

Where does this leave us?

Whichever way you cut it, the gist of the matter is that we’re working against and destabilizing natural systems around us. We’re taking too much, too fast, and too indiscriminately for the environment to cope.

I like to think of nature as an economy. Every species has its place in the wider system and gets paid (consumes resources) for the work it performs (its ecosystem role). In this analogy, sadly, humanity is a huge monopoly. We insert ourselves into previously-free markets (ecosystems) and extract as much as possible from them while providing as little benefit as we can get away with. Sure, there are fluctuations in this market that have nothing to do with us, but their influence pales in comparison to ours.

Because of the scope and speed with which we transform the world around us, natural systems don’t have the time to clean up the mess. Climate change is the product of this imbalance, but it’s not the only one: rising rates of extinction, aquifer drainage, soil degradation, or adaptations in animal wake cycles, camouflage patterns, and geographical distribution are all signs that we’re not managing nature but exploiting it.

Thankfully for us and our fancy opposable thumbs, the fix is actually quite simple in theory — use fewer resources, or do more to support natural systems. Or both. Techniques like carbon capture help reduce the strain we put on the environment by lowering overall CO2 levels (which are currently being processed by plants). Alternatively, initiatives like The Trillion Trees campaign are an example of how we can support ecosystem health and function to achieve the same goal. We could produce less plastic to reduce our resource consumption, or we could improve and widen recycling efforts to reduce waste and lessen our impact on natural systems.

Personally, my gut feeling is that supporting natural functions rather than reducing our resource use should lead the way. Ideally we’d do both but, with close to 7.8 billion people alive at the moment — all of us working for a happier, more bountiful life, and having kids — there’s only so much we can give up. In my view, we should strive to use as little as possible to the greatest effect, while working to mitigate our impact on the environment to the best of our abilities because that’s a middle ground most of us are willing to accept.

Of course, for that to happen, we need to commit to it. The scientific community has reached a consensus on climate change — it’s happening, and it’s our fault — but the political and civil discourse has yet to do the same. In the meanwhile, how would you go about combating climate change? Let us know in the comments.

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