This post is a continuation of my multi-post series exploring the spectrum of climate change skepticism. So far we have covered Skeptics of Occurrence, a segment of the population who don’t believe climate change is occurring at all. The next group we will explore are the Skeptics of Cause. This group of skeptics believe that the earth’s temperature is rising, but they are not convinced humans are the primary cause. Why aren’t they convinced that human activity is the cause of climate change? Like our last segment, there are multiple motivations for their position. 

Some members of this group are driven by chronic antagonism (detailed in our Skeptics of Occurrence post, you will see this motivation across all the segments). Chronic antagonists in the Skeptics of Cause segment are still motivated primarily to spite the opposition. However, unlike chronic antagonists in the Skeptics of Occurence cohort, they are willing to concede climate change is occurring because as long as humans aren’t responsible for climate change, then there is no basis for opponents to advance the policy changes that threaten their views and beliefs. 

Like the previous segment there are also individuals motivated by independent research. These independent thinkers dispute analyses that conclude that human activity is the dominant cause for climate change.

The remaining members of this segment are caught in a cognitive bias born from knowing just enough to accept climate change is occurring, but not enough to believe humans are the primary cause. It’s no surprise this last group exists. Understanding that the earth’s climate is getting hotter is fairly straightforward. However, understanding why scientists believe humans are the cause for rising temperatures requires more effort, and many people lack the time and/or will to see it through. Also, there are naturally intuitive arguments that make it easy to be skeptical about humanity’s role in climate change. Many of us learned in school about the climate naturally alternating between ice ages and greenhouse periods. Why couldn’t this recent rise in temperature just be part of this natural cycle? Aren’t those natural fluctuations also backed by science?

I’ll be honest, I belonged to the last group when I first started paying attention to news reports and articles on climate change. It took a few day’s worth of digging to understand why climate scientists are so confident humans are the dominant factor in the rise of earth’s temperature. I won’t go into the nitty-gritty details of climate science, but I can summarize my findings in Q & A format below. 

How do we know the earth’s temperature is rising? We have recorded temperatures since the 1850s that show that average temperatures are rising. We also have measurements of CO2 concentration that show CO2 concentration has been rising since the 1950s. Higher concentrations of CO2 in the atmosphere result in higher temperatures because CO2 absorbs heat leaving the earth and re-emits that heat back at earth. 

Aren’t those time spans too short to be convincing of any meaningful trend? If that were the only data we had, I would agree. But we also have other evidence that provides insight into the state of the atmosphere thousands of years ago. For example, scientists have analyzed air bubbles trapped in ice from the last 1000 years that show CO2 concentration levels were relatively consistent before the 19th century. Then, CO2 levels began to rise steadily in the 19th century and then exponentially throughout the 20th century. 

Ok, but how do we know CO2 is the main cause for the temperature rising now? Aren’t there other things that contribute to the temperature rising? There are! The amount of solar energy being emitted by the sun increases Earth’s temperature. Or, increases in volcanic activity also cause the temperature to rise because when volcanoes erupt, they release more greenhouse gasses which trap more heat in the atmosphere. The reason we are focused on CO2 levels is because the other factors have seen minimal change over the last century, while CO2 levels have increased. Since CO2 is the only factor that is significantly rising, it’s reasonable to conclude that it is the primary driver behind the rising temperature.

Ok, but how do we know humans are responsible for the increase in CO2 in the atmosphere? The evidence that humans are likely the cause of increased CO2 is strong. We know automobiles and energy plants emit huge amounts of CO2 into the atmosphere. But, on top of that, CO2 from burning fossil fuels has a particular signature that distinguishes it from other sources of CO2 (e.g. CO2 released by deforestation). Basically, when fossil fuels are burned, the CO2 they release has a very low amount of a certain carbon isotope. The proportion of this isotope in the atmosphere is decreasing even while overall CO2 levels are increasing. This suggests the increases of CO2 are driven by a source that is low in this particular carbon isotope, i.e. CO2 from burning fossil fuels. This is a pretty strong signal that human activities are the dominant factor for the increases in CO2, which in turn is responsible for increasing temperatures.

Having those questions answered convinced me that humans are the major contributor to climate change. However, members that still belong to the Skeptics of Occurrence segment haven’t had a chance to look into the data themselves and some wouldn’t change their mind even if they did. That being said, even people that do believe humans are responsible for climate change can still be labeled a climate skeptic in today’s world. The reason for this will become more evident as we look at our remaining groups of skeptics. The discussion will gradually shift focus from facts presented by climate science to personal beliefs, relative priorities and political motivations.