 Much of the discussion around climate change focuses on greenhouse gas emissions. To understand how we're changing the climate, we must first understand the role greenhouse gas emissions play. The greenhouse effect is a well-understood phenomenon which makes the earth uniquely suited for life as we know it. Our atmosphere creates a warm blanket of sorts around our planet. It allows us to hang on to some of the sun's radiation long enough to keep us warm enough to live, produce food, and now, unfortunately, mess with the planet's natural balance of greenhouse gases. The greenhouse effect is a very good example of when too much of a good thing is anything but great. So let's take a look at how the greenhouse effect functions properly, and then we'll take a closer look at what's happening to it now and how that's changing our climate. The sun produces very intense shortwave radiation, most of which passes rather easily through our atmosphere. Once it enters the atmosphere, there are several different ways it behaves. Some of it is absorbed and re-emitted in all directions by greenhouse gas molecules in the air before it ever even reaches the surface of the earth. This helps warm both the surface of the earth and our lower atmosphere. About half of that intense shortwave radiation coming from the sun is absorbed by the ground, clouds, and other surfaces. These surfaces absorb that energy and then release it back toward the atmosphere in the form of longer wave radiation, which is less intense. These less intense wavelengths are less likely to penetrate back out through the atmosphere and therefore end up being absorbed by greenhouse gas molecules, helping keep things at that nice, temperate, suitable for life climate we all need. The problem arises, though, when the balance of greenhouse gas molecules in our atmosphere is altered. Human activities like fossil fuel combustion and deforestation upset this balance by increasing the amount of these heat-trapping gases. And the more of those gases there are in the atmosphere, the more opportunity they have to warm things up. This is where the concerns about climate change begin. Ice core data helps us reconstruct gas concentrations throughout history. For the last 400,000 years until the Industrial Revolution, CO2 concentrations ranged from about 200 to 280 parts per million. That rapid increase in human combustion of fossil fuels since the Industrial Revolution, though, has increased carbon that has otherwise been locked up underground for thousands, if not millions of years. This throws the natural greenhouse effect out of kilter. Recognizing the role greenhouse gases play in our global climate system helps us understand the actions we must take to address climate change.