Today on How to Explain Climate Change to Your Own Mother, we will be treading into some rather murky territory. Previously, I have covered the physical reality of climate change: greenhouse gases trap in heat from the sun, and human activities spew out more greenhouse gases than can be naturally fixed into non-greenhouse gases. I’ve also shown a bit of evidence validating the reality of a changing climate, documented across the board by scientific instruments and geological structures alike. The past and the present are relatively clear, but what does a future influenced by a rapidly changing climate look like? When will climate change truly start affecting your life? Scientists use quantitative modeling methods to help inform their answers to these questions, but be careful! The future according to these climate models is a magical land—somewhat transparent, but with uncertainty lurking around every corner.
How do scientists begin creating a model? What is modeling anyway? Well, as it turns out, physical phenomena of all kinds can often be reduced down to a mathematical formula. If something is added to a system, that system changes, and we can predict these changes and outcomes with calculations based on the system’s properties. For instance, when heat is added to a substance, we can calculate how much that substance will expand due to the increased movement of its molecules. Models like these are verified by experimenting with real life data and measuring it against its predictions. Good models are calculable, applicable, and important for questions like, “If I build a structure out of steel, how much will it shrink in the wintertime and expand in the summertime?”
These types of mathematical models can also be applied to climate systems. Remember we talked about Svante Arrhenius, the early climatologist who demonstrated the carbon dioxide’s greenhouse effect? This physical property of carbon dioxide is what many climate models are founded on today. If we know that carbon dioxide is responsible for much of the greenhouse effect, the amount of carbon dioxide in the air, and the amount of incoming heat this gas holds onto, then it stands to reason that we should be able to figure out how our global temperature might change if we add more of this greenhouse gas to our atmosphere…right?
As you may have guessed, however, our entire climate system is a little more complicated than that. First of all, carbon dioxide is not the only greenhouse gas being added rapidly to our atmosphere. Other greenhouse gases, like methane and water vapor, also have the ability to trap heat with varying efficacy. This property, termed Global Warming Potential, must be accounted for when examining the total amount of added greenhouse gases to the atmosphere.
So now we have a few different gases contributing to the greenhouse effect. However, plugging in a certain amount of greenhouse gases to our climate change model will still not give us a clear, linear idea of our Earth’s future average temperature. The complications associated with this outcome are astounding. Take into consideration the effect of albedo, where dark colors absorb light, and light colors reflect it. Earth’s ice caps, being gigantic and bright white, act as natural reflectors of sunlight. If more greenhouse gases in the air cause slightly warmer temperatures, and these temperatures cause ice caps to melt, the Earth absorbs more sunlight than reflecting it, causing potentially even higher temperatures and more ice cap melt! Albedo is not the only example of a spiraling cycle taken into account when making predictive models.
There are a number of other factors governing the Earth’s climate aside from rapidly rising greenhouse gases in the atmosphere alone. Natural, cyclic fluctuations in ocean circulations and temperature, like El Niño or the North Atlantic Oscillation, can cause extreme weather and be very difficult to tease out from human-induced causes. Even less predictably, large volcanic eruptions can release huge amounts of gas and ash into the stratosphere, altering the amount of sunlight that reaches the Earth. The eruption of Mount Pinatubo in 1991 was so large that its sulfur dioxide cloud covered the Earth, cooling the planet’s surface temperature for the next three years.
There are many parameters to consider when trying to determine the Earth’s future average temperature, but this article has really only scratched the surface of the mountain of these parameters. Earth’s climate system is so large and complex, it sometimes seems miraculous that any sort of clear trend can emerge from the whirling torrent of background data. The one essential thing to remember when hearing predictions about the future of the Earth’s average temperature, sea levels, or precipitation patterns, is that these predictions are steeped in uncertainty.
That’s not to say that scientists and statisticians are sitting forlornly in front of their computers, throwing their hands up in the air, or spinning around with their eyes closed, until their finger lands a plausible result. No, this is a precisely calculated uncertainty–some outcomes of anthropogenic climate change are more likely to occur than others, but no single future is 100% certain. The likelihood of these different outcomes change as we change the parameters of our models: what happens if we cut all of our greenhouse gas emissions? What happens if we continue under a “business as usual” scenario? What if there is El Niño or volcanic event? Taking all of these parameters into account gives us a graph that looks something like this:
It’s complicated. It’s uncertain. And, yes, it’s pressing that we think about how our immediate decisions relate to one of these futures. However, is mom jumping out of her seat yet to start making significant behavioral and policy changes that would lessen greenhouse gas emissions? Probably not. Hey, neither am I. Turns out, the one topic that is even more complicated and uncertain than modeling future climate predictions is the human psyche itself, a reason why climate change may be the hairiest problem of all time. So stay tuned–it’s going to get juicy.