 Does Mars cause fires or do fires cause sparks? This is a difficult question because both statements are true. Questions involving cause and effect can be tricky, and this is true in discussions of climate change as well. In order to understand major climate changes such as ice ages, studying past climates through the ice core record can help scientists identify causes and effects more clearly. The most famous ice core is from Vostok Station in East Antarctica. Ice core is over three kilometers long, goes back over 400,000 years, and shows us four different ice ages. Another famous ice core called Epica reaches back nearly 800,000 years. In looking at the core data, we can immediately see that temperature and carbon dioxide have similar patterns. When CO2 levels are high, the earth is warmer. When CO2 levels are low, the earth is cooler. But correlation is not causation. Does CO2 cause warming or does warming cause CO2 to increase? In fact, both statements are true. The ice core record tells us that a bit of warming caused CO2 to increase, which in turn caused warming in a reinforcing feedback loop. Confusion about the ice core record has spawned the myth that because warming caused CO2 to rise, CO2 cannot cause warming. This myth is an example of a false dichotomy, also known as a false dilemma. The dilemma is false because it's not a case of either or, both things can be true. So how does global warming lead to increased CO2 levels? Consider the following. When water is heated, gases such as carbon dioxide are driven out because water can't hold as much gas when it's warm as when it's cold. You can check this fact by using two cans of soda. When opened, a warm can will fizz much more than a soda that has been chilled. In the same way, a warmer ocean releases much more carbon dioxide into the air. And the ocean holds a lot of carbon. This release of carbon dioxide creates a feedback mechanism. Warming oceans increase atmospheric CO2, and CO2 increases global warming. But how did this feedback loop start? Let's take a closer look at the end of the last ice age when our earth warmed up to our current balmy temperatures. That warming started about 20,000 years ago and took from 7,000 to 8,000 years to progress, a relatively short time on geological time scales. When we zoom in on that range in the Voss.core, we can see that Antarctica apparently started warming before carbon dioxide increased. This observation connects to the myth that temperatures rose before CO2, so CO2 can cause warming. But wait! Antarctica doesn't represent the whole planet. We have data about the end of the last ice age from other sites. In this figure, Shacken and his colleagues combined all of the available data to create a global picture of temperature and CO2 increase. From their data, we can see that the dramatic increase in CO2, those yellow dots, came before most of the warming of the planet, the blue line. The temperature increase lags CO2 because so much heat is absorbed by the ocean. Since the oceans are so big, they take hundreds of years to heat up. This data clearly points the figure at CO2 as the primary cause of global warming, but we still have two questions. What started this feedback loop? And why did Antarctica warm before the rest of the Earth? These two questions are related and scientists love to figure out mysteries like this. What they found is that changes in the Earth's orbit started a bit of warming in the northern hemisphere. That heating caused the oceans to start releasing the stored CO2. The CO2 built up slowly at first. Its heat-trapping effect built up, too. This feedback got stronger as CO2 caused heating and the heating caused the oceans to release more CO2. The data tell us that the warming was not even over the whole globe. The melting of the massive glaciers of the northern hemisphere changed the ocean circulation and trapped the heat in the southern hemisphere. Antarctica started warming first, while Greenland actually cooled a bit at the same time. Let's return to the myth that CO2 cannot cause warming, because some warming was observed before the major increase in CO2. This myth is an example of a false dichotomy or false dilemma. The myth can be rephrased as two options. Either increase CO2 caused warming or warming caused increased CO2. A false dilemma makes you believe that there are only two possible options and that one negates the other. But science reveals a third option that allows for both of these statements to be true. An increase in CO2 caused warming and warming causes an increase in CO2. And the explanation from science is that changes in the Earth's orbit triggered warming that started the feedback loop that increased both CO2 and warming.