Global warming, the greenhouse effect, climate change...these buzzwords have been echoing through the media for years now. We're constantly bombarded with images and stories.

Melting glaciers all over the globe and sea ice that diminishes every summer...sea creatures that can't survive in warmer waters and decreasing fish stocks that threaten the livelihood of those who depend on them...raging  wildfires and heat waves that kill or sicken thousands of people...changes in disease patterns that make humans more susceptible to serious illnesses...more  devastating  floods in some areas and longer droughts in others...

These events all have a dramatic impact on society and modern life, and projections by climate scientists suggest that topics like these will continue to be in the headlines.

However, as with much of science news, there are often stories that seem contradictory and confusing.

To sort this out and understand the background behind these stories, we need to answer questions like:

• Is climate change real? Can humans really alter Earth's climate, and how does that fit with our knowledge of how climate has changed naturally throughout history?
• How do we know? How have scientists come to their current understanding of climate change?
• Why should we care? What are the things that might change in the future that will affect us and future generations?
• How sure are the scientists? How much agreement is there among them?
• And, what steps can we take next?

Scientists have been working to answer these questions for decades.

In some ways, it's like putting together a giant puzzle. Each individual piece tells you little, but as the pieces are assembled, the puzzle becomes a recognizable picture, even if some parts are still unfinished. Today most climate scientists agree that the puzzle pieces clearly show that human-induced climate change is happening.

In this module, we'll dump all the pieces out on the table to let you look at them, explore how scientists are fitting them together, and see where a few are still missing.