1 Max Planck Institute for Meteorology, Bundesstrasse 53, 20146 Hamburg, Germany.
2 Centre of Excellence for Climate System Science, Monash University, Level 2, 9 Rainforest Walk, Clayton Campus, Wellington Road, Clayton, VIC 3800, Australia.
3 Laboratoire de Meteorologie Dynamique (LMD/IPSL), CNRS/UPMC, Sorbonne University, Tour 45-55, 3eme etage; 4 place Jussieu, boite 99 75252 Paris Cedex 05, France.
4 Department of Atmospheric, Oceanic & Earth Sciences, George Mason University, 4400 University Drive, Mail Stop: 6C5, Fairfax, Virginia 22030, USA and the Center for Ocean-Land-Atmosphere Studies, George Mason University, 4400 University Drive, Mail Stop: 6C5, Fairfax, Virginia 22030, USA.
5 Department of Earth, Atmospheric and Planetary Sciences; Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 54-1712, Cambridge, Massachusetts 02139-4307, USA.
6 Department of Meteorology, University of Reading, Reading RG6 6BB, UK.
7 Climate Change Research Centre, UNSW Australia, Sydney, NSW 2052, Australia. Corinne Le Quéré is at the Tyndall Centre for Climate Change Research, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
8 NASA Goddard Space Flight Center, Cryospheric Sciences Lab, Mail Code: 615, Greenbelt, Maryland 20771, USA.
9 International Council for Science (ICSU), 5 rue Auguste Vacquerie, Paris 75116, France.
10 ETH Zurich, Institute for Atmospheric and Climate Science, CHN N11, Universitätstrasse 16, Zurich 8092, Switzerland.
11 WCRP Joint Planning Staff, World Meteorological Organisation (WMO), 7bis, avenue de la Paix, Case postale 2300, CH-1211 Geneva 2, Switzerland.
Human activity is changing Earth's climate. Now that this has been acknowledged and accepted in international negotiations, climate research needs to define its next frontiers.