Climate change has now taken center stage in our public discourse. And rightfully so. The environmental, social, and economic impacts of climate change – and society’s response to them – will literally shape the future of the planet.
What is climate change exactly?
We all kind of know: burning fuel puts CO2 in the atmosphere and that makes the world warm, which is bad.
But if you look a little deeper into the topic, you’ll see that there’s a lot more going on. You’ve probably heard references to an assortment of topics, such as solar intensity, rising ocean levels, and methane just to name a few, without feeling like you got the whole picture.
We wrote this primer to help you make sense of it all.
In Part I, we’ll discuss what factors affect the Earth’s temperature and why there is some inherent uncertainty around the ultimate effects of climate change. In Part II, we’ll cover the range of predicted temperature increases and how rising temperatures affect the plant. Finally, Part III will give an overview of what we are doing to stop it.
As a quick note: we’ve included enough information here to help you become a critical thinker on this topic, but have omitted any information that requires prior knowledge or training.
Now, without further ado, let’s take it from the top.
The factors that control climate
1. Solar Irradiance – does the strength of the sun change?
Yes, the strength of the sun (solar irradiance) actually changes over time. And yes, it has likely increased since pre-industrial times. This has led some to suggest that the recent warming of the planet has primarily been driven by factors outside of human control.
However, evidence shows that the increase in solar irradiance has had a relatively small role (though not zero role) in the recent warming of the planet. Global temperatures have increased clearly and sharply since the 1950s, when solar irradiance has been flat.
2. Earth’s movement – do changes in earth’s orbit cause climate change?
The movement of the earth relative to the sun can have great impacts on climate. There are two fundamental concepts to first grasp regarding the impact that rays from the sun have here on earth, related to 1) distance and 2) angle of impact.
- Distance: In short, distance from the sun is not linearly correlated with the strength of solar energy received on earth – there is an exponential relation. This means that if you double the distance between the sun and our planet, the energy intensity received on earth decreases by a factor of 4.
- Angle: The angle of arrival of solar rays also affects how much energy is received. This is why the temperature at the equator is far higher than the temperature at the poles. Each “ray” of energy is spread out over a greater surface area at the poles than at the equator.
These concepts are important because they predict that the positioning of the earth relative to the sun can greatly impact our climate. And in fact, earth’s distance and tilt changes at regular intervals. These intervals, known as Milankovitch cycles, are illustrated below, and explain the prehistoric changes in climate (e,g., the ice age).
Could the current warming be explained by these Milankovitch cycles?
Not in a meaningful way. As you see in the diagram above these cycles occur in the scale of tens of thousands of years.
3. Greenhouse gas effect and climate change
Alright, here’s the big one. When the earth receives rays from the sun, it absorbs much of the electromagnetic energy, but reflects some of it back into space. Think about taking a hot shower on a cold day. When you step out of the shower, you start radiating heat into the air around you and cool off. That’s what the earth does with the heat it gets from the sun.
Now imagine throwing on a robe or a blanket after you get out of that hot shower. This will trap in some of the heat from the shower and keep you warmer for longer. This is what greenhouse gases (GHGs) do for the earth. As the earth radiates energy back into space, it encounters the GHGs in the atmosphere, which absorb some of this energy and radiate it back to the earth.
Well then why don’t GHGs protect us from solar radiation in the first place? If they trap in heat, shouldn’t they also keep heat out?
Turns out incoming solar radiation has a higher frequency (short wave) and passes right through the GHGs, while outgoing radiation that has a lower frequency (long-wave) gets trapped.
While the precise impacts of the greenhouse gas effect is extremely hard to determine, the directional effect is clear. Scientists have been able to measure that the long-wave radiation leaving the earth has been decreasing, implying that more and more radiation is getting sent back down to earth. Studies of ice cores have also shown that there is a high correlation between carbon in the atmosphere and the earth’s temperature
Below is a chart that captures GHG emissions over time. We discuss the different gases in the third article of our climate change series, which discusses the challenges of fighting climate change.
For now, let’s keep going. This isn’t the end of the story.
4. Albedo – what is it, and what is a feedback effect?
Albedo refers to the reflectivity of the Earth, and may be the most interesting and increasingly critical factor governing climate. The earth does not absorb all of the solar energy that hits its surface. In general, whiter surfaces reflect more energy than darker ones (think about wearing a black shirt in the summer). Also, a surface reflects more when light hits it at an angle, as opposed to head on. For terminology, high albedo means that a surface is highly reflective and a low albedo means the opposite.
Why is all of this important? The higher the collective albedo of the earth, the less the earth will warm. Important sources of albedo include snow, ice, cloud cover, and aerosols (e.g., volcanic ash, smoke, air pollutants).
Moreover, albedo can have strong feedback effects.
Let’s take an example – say solar irradiance increases, causing ice to melt. The earth’s albedo then decreases because there is less ice to reflect sunlight. This, in turn, causes the earth to absorb more solar energy, which then causes higher temperatures…which melts more ice. This is called a positive feedback effect, as it amplifies another climate change factor.
Feedback loops can also be negative. A negative feedback loop is a phenomenon that dampens another climate change factor. Take the example above where solar irradiance causes temperatures to rise. As temperatures rise, however, evaporation from the ocean increases. This in turn increases cloud formation, which increases albedo. The negative feedback loop mitigates the full effect of the increased solar intensity. Ironically, evaporation also has a separate positive feedback effect, as it increases the water vapor content in the air and traps heat. At this point it is unclear the net effect of these two competing feedback effects.
It is important to note that the interplay between these feedback effects amplifies the uncertainty about climate change. Any error or uncertainty about warming through the GHG effect will always result in more uncertainty about what feedback effects may be triggered.
Speaking of uncertainty, let’s talk a little more about aerosols.
5. Aerosols – what’s the deal there?
Aerosols are very small solid particles (or liquid droplets) suspended in air or another gas. They can be both natural or man-made (including things like fog, dust, smoke, air pollutants) but most often refer to pollution caused by burning fossil fuels.
Interestingly, aerosols may actually decrease the temperature of the earth by increasing its albedo. Aerosols in the air (pollution) ironically shield the Earth from incoming shortwave radiation from the sun. They also contribute in a number of ways to the formation of clouds, which also provide cover from the sun.
As of this writing there is great uncertainty about the magnitude of the aerosol effect. Aerosols interact with solar radiation in 7 different ways, and the cumulative impact of each of those is still unclear.
Putting it all together – climate change models
Given the complexity of climate science, it’s not very surprising that the latest models predict a wide range of expected warming–everything from less than 2C to 6C. As you might be able to guess after reading this article, there are two major sources of uncertainty: 1) level of GHG emissions (and mitigation) in the future, and 2) impact of feedback loops.
That’s not to say that the likelihood of every possible outcome is the same. The figure above compiles a number of possible outcomes suggested by climate models. The horizontal axis is the expected temperature change, and the height of the curve reflects probability. As the distribution of possible outcomes shows, the likelihood of higher temperature is certainly higher (the “right tail” under the curve is longer than the left tail). These are not the odds you’d want with your bookie.
So what does all of this actually mean for us as residents on this planet? In part two of our three-part series we’ll explore the effects of climate change, including some of your most burning questions, like: Are we all going to drown? Why does my uncle keep telling me sea levels are actually falling in the arctic? Will there really be more hurricanes?
