The hashtag #COP21 started trending over the weekend ahead of the United Nations’ conference on climate change. What is COP21? It stands for the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change. World leaders like U.S. President Barack Obama and Chinese President Xi Jinping spoke about this year’s conference as a new beginning. Xi called the summit “a new starting point.” Obama said, “Our generation may not even live to see the full realization of what we do here.” But it’s a tweet from outer space that has received all the attention. American astronaut Scott Kelly wrote, “From space, we are privileged to see the beauty of Earth, but also our impact on its environment.” The tweet was liked over 4,000 times in seven hours.