Why climate change is urgentWhy climate change is urgent Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2015-11-072014enCarbon dioxide (CO2) is the main greenhouse gas (GHG) in the atmo- sphere responsible for long-term global warming, and scientific evidence indicates that the current CO2 concentration is proba- bly the highest in the last 15 million years (World Bank 2012)—more than 391 parts per million (ppm), com- pared to the preindustrial level of 278 ppm. CO2 emis- sions grew 1.1 percent per year from 1990 to 1999 but since 2000 they have been growing by more than 3 per- cent per year (Gowdy 2010). The National Oceanic and Atmospheric Administration (NOAA) reported a reading of CO2 at Mauna Loa of 400.03 ppm on May 9, 2013, crossing for the first time the 400 ppm mark.1 Global warming due to past anthropogenic CO2 emis- sions is irreversible for at least 1,000 years, and current and future CO2 emissions will result in additional warm- ing (Matthews and Solomon 2013). The international community has set the goal of stabilizing global warm- ing at no more than 2°C above preindustrial levels by 2100, while the Small Island Developing States (SIDS; www.sidsnet.org) have set it at 1.5°C. But given cur- rent emission levels and minimal international action to mitigate climate change, “there is roughly a 20 per- cent likelihood of exceeding 4°C by 2100” (World Bank 2012, p. 1). It is still possible, however, to keep global warming within tolerable limits through the use of appropriate technologies to replace fossil fuel consumption with other energy sources and the application of interna- tional political will to change course and control cli- mate change. Any delay of such action will commit the planet to higher and higher temperatures that will become irreversible in the foreseeable future. The likely consequences will be dire.http://creativecommons.org/licenses/by/4.0/The Bridge 44330-37 Kouikoglou Vasilis Κουϊκογλου Βασιλης Grigoroudis Evangelos Γρηγορουδης Ευαγγελος Yannis Phillis Φιλλης Ιωαννης Kanellos Fotios Κανελλος Φωτιος Papaefthimiou Spiros Παπαευθυμιου Σπυριδων Madni Asad M. National Academy of Sciences Climate change