Dr Andrea Sella of University College London demonstrates how one of his favourite molecules, carbon dioxide, reacts with water. More than just another pretty demonstration, the experiment acts as an alarm signal for what we are doing to our world. As rising levels of CO2 dissolve in our seas many species -- especially those in coral ecosystems -- are unable to adapt to increasingly acidic waters. The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter