Following from last week’s introduction to our climate change series, this week we have an article explaining how climate change actually works and why it happens. Firstly, we will be drawing on our sister planet Venus as an example.
Earth’s Evil Twin
Earth and Venus are, on the face of it, quite similar planets. They are roughly the same size, about the same mass, and they orbit at similar distances to the Sun. But when you get down to their surfaces, you find two very different worlds.
On Earth we find huge oceans of liquid water, a planet teaming with life, and an atmosphere that keeps us safe and allows life to flourish. On Venus however, we find a very different world, a hellish world. The surface is a dry wasteland, baking in temperatures of over 450ºC, with a thick atmosphere of carbon dioxide that rains sulphuric acid. But around 4 billion years ago, when the Sun was barely half a billion years old, Venus is thought to have been much like the Earth is today. So what happened to Venus that changed it so dramatically?
What happened was a change in Venus’s atmosphere, which caused a runaway greenhouse effect. The oceans on Venus were gradually boiled away as the Sun increased in brightness during its early life. These clouds, similar to those we have on Earth only a whole oceans worth, created a really strong greenhouse effect.
The Greenhouse Effect
The greenhouse effect occurs when a gas traps heat in the planets atmosphere. Adding a greenhouse gas to your planets atmosphere is kind of like wrapping your planet in a blanket, trapping heat in. For a planet to be in a nice balanced state, it needs the amount of heat energy it receives from its star to be balanced with the amount of energy it can lose. A greenhouse gas makes it harder for the planet to lose the energy again, meaning it’s no longer in balance, the amount of energy it gains is now more than it can lose. This imbalance raises the temperature.
A greenhouse gas works by absorbing infrared light coming from the planet, trapping it. This is a problem because planets shine brightly in the infrared, because anything with a temperature will give off light to its surroundings. One of the most visibly obvious examples of this is a toaster. As the wire heats up, it begins to glow, first a dull red and then a brighter red. We see this heat as visible red light at around the 600ºC of a toaster, but lower temperatures objects emit light too, only in the infrared part of the spectrum rather than the visible. This is where greenhouse gases come in. They are really good at catching the infrared light that planets like Earth and Venus glow with, stopping that light from escaping. Gases like carbon dioxide (CO2), methane and water are particularly good at absorbing this light, reflecting it back to warm the planet instead of letting it escape into space.
With greenhouse gases in an atmosphere, the planet can’t balance the energy it gets from its star with how quickly it can lose it again. For Venus, as this imbalance grew the oceans boiled, trapping even more heat in. This is what we call a runaway greenhouse effect: the hotter it gets, the more greenhouse gases enter the atmosphere, which makes it even hotter, which releases yet more greenhouse gases, which… The diagram on the left shows how this circle just keeps going and going, releasing more and more greenhouse gases and continuing to increase the temperature. Temperatures on Venus rose so high that carbon that had been trapped in rocks escaped into the atmosphere, which then reacted with oxygen, creating more even greenhouse gases in the form of carbon dioxide, the gas that dominates its atmosphere today. All this extra gas leads to high atmospheric pressures, with the pressure at the scorched surface of Venus being over 90 times.
Earth’s Changing Climate
It is a natural and good thing for an atmosphere to have some amounts of greenhouse gas. Without an atmosphere, Earth would have an average temperature of just 6ºC. Instead, thanks to our atmosphere, we have temperatures varying from around -90ºC in parts of Antartica, to around 70ºC in the deserts of Iran. Fortunately, most of the planet is nowhere near these extremes of temperature, with the average temperature being around 15ºC. However, this average temperature is rising.
This graph shows the average increase in temperature over the previous decade. There are are occasions, such as the 1910’s and 1950’s, where temperatures dropped, but generally things have been warming up. This is a trend that has continued since the industrial revolution.
Over 97% of climate change scientists agree that human activity is the primary cause for this increase. We are adding greenhouse gases to the atmosphere at an unprecedented rate thanks to our incessant thirst for oil and energy, with 100 million barrels of oil being consumed each day, releasing carbon dioxide and other gases into the atmosphere.
The exploding global population is accelerating this. The number of humans on Earth has nearly doubled in the last 50 years and is expected to reach 8 billion people by the early 2020’s. That’s double the amount of food and energy the planet needs to provide, in a world where the average person already demands nearly 3 times the energy they would have used in a day just 100 years ago.
To provide food, vast areas of natural woodland are being decimated in order too clear space to grow crops and rear livestock. Every minute nearly 50 football pitches worth of forest are destroyed, removing our best, natural, way of recapturing greenhouse gases, and replacing them with sources of even more greenhouse gases. To produce a kilogram of beef, the equivalent of about 35kg of CO2 is released. That’s about the same as the amount of CO2 released from powering a TV for 4 hours a day, for an entire year.
It’s clear from the evidence that the last couple of centuries of human activity have changed the planet, possibly irrecoverably. The gases we have put into our atmosphere have warmed the planet and climate systems that have been steady for millennia are changing. The icecaps are shrinking year by year. As the ice melts, pockets of greenhouse gases trapped in the ice for thousands of years are being released, only making the problem worse. As the ice melts, sea levels rise. The image below shows the decline in arctic sea ice levels from 1980 (bottom) to 2012 (top).
Periods of extreme drought and flooding are endangering millions. The changing climate is contributing to the first mass extinction event our planet has seen since the dinosaurs were wiped out.
As things stand, we’re doing to Earth what Venus did to itself. We’re changing our planet faster than it can cope with the change, and as things go on, it gets harder for the planet to cope.
But it’s not too late for Earth, it doesn’t have to be doomed to become the hellish world we see on Venus. Every little thing helps. Turning off a light that you don’t need? Buying local produce that hasn’t had to be shipped thousands of miles to get to you? Walking instead of taking the car? All these simple things, if done by everyone, make a huge difference.
Climate change is a global problem, and it needs a global solution. Switching to clean sources of energy, such as solar or wind power, will save our atmosphere from being further polluted by the burning of fossil fuels. Caring for and regrowing the woodland we have destroyed will allow some of the effects of climate change to be slowly repaired. Reusing and recycling the resources we already have will save having to produce more. But it’s something we all have to accept responsibility for, and we all have to start taking action now.
We share the same planet and it’s the role of everybody to look after it, for now and for the future.
Not so fun fact:
In the time it has taken you to read this article, over 300 football pitches worth of forestation will have been destroyed, and the equivalent of around 300,000 tons of carbon dioxide will have been released into the atmosphere. That’s nearly the weight of the Empire State Building.
Article Written by Tom Watts