Source: https://www.nytimes.com/2015/03/17/science/the-new-optimism-of-al-gore.html?_r=4&mtrref=undefined&assetType=nyt_now&mtrref=www.nytimes.com&assetType=nyt_now&mtrref=www.nytimes.com&assetType=nyt_now&mtrref=www.nytimes.com&gwh=647B002AAEC5ADEDEFDC5E5017FD339F&gwt=pay&assetType=nyt_now