And would Scarlett sign on if she hadn't personally vetted the science?

Scarlett Johansson And Others Sign Oxfam Climate Change Letter

Most recently Oxfam recruited nineteen actors, musicians and activists – including stars like Scarlett Johansson, Annie Lennox, Colin Firth and Kristin Davis — to sign a climate change letter written to world leaders who attended the UN climate negotiations in Poland.
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With so many people getting involved, it’s hard to believe that only a few years ago the verdict was still out on climate change.