You can endorse the article on http://scientistswarning.forestry.oregonstate.edu/.
What's the purpose? Read the quote.
If you are a scientist from any scientific discipline (e.g. ecology, medicine, economics, etc.), we invite you to endorse our Viewpoint article in the journal Bioscience entitled “World Scientists’ Warning to Humanity: a second notice” by Ripple et al. (2017). In doing so, you will be included in the full list of scientists who have endorsed this article and 15,000+ scientists from 184 countries who signed the article before the publication deadline on Oct. 23, 2017. Before endorsing, we ask that you view our 1,000-word article by clicking “Read the Article” tab below (the text can be read in 6 minutes). When you click “Endorse the Article” and add your name, you will be indicating that you generally agree with our article, helping get this message to world leaders.