Although we have coped with air quality problems such as combustion emissions, photochemical smog and depletion of the ozone layer by putting preventative measures in place when the symptoms got bad enough, climate change is more complex and intense. If you are young enough while you are reading this book to expect to live well into the second half of the twenty-first century, then you will probably experience the greatest level of environmental change, and the greatest efforts by humans to deal with it, that we have ever experienced. Words such as climate change, global warming and greenhouse gases have become integral to conversation on topics such as environmental protection and sustaining human existence on Earth. In this chapter we will look at the physical causes, and at some of the possible consequences of these changes, specifically in the context of atmospheric emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) – collectively known as the key greenhouse gases (GHGs, described in more detail in Section Nearing the end of the twentieth century, it became evident that the mankind have now entered an era where our releases to the atmosphere have the potential to change the whole of Earth’s environment more than ever before.