What is climate change? Is it a product of natural cyclical variations in the Earth’s ecological systems, or is it a consequence of human activities? What are the implications of climate change for the international system? How serious are the ramifications of climate change for the continuity of modern industrial civilization? This chapter begins by confronting the major public-media debates regarding the causality of climate change, reviewing the main arguments that challenge the idea that contemporary global warming is due to fossil fuel emissions and therefore human-induced (anthropogenic). The relevant scientific literature is explored to discern whether we can be sure that climate change is happening, and why.