I'm spending the rest of the year reporting on a little-known but hugely important number: 2 degrees Celsius. That's the agreed upon threshold for dangerous climate change. I need your help to do it. Look for about one e-mail update per week as I explore what the world will look like if the climate warms 2 degrees -- and what would stop us short of that mark. Send ideas to john.sutter@cnn.com or @jdsutter.
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