Abstract

Experiments allow the testing of elaborate hypotheses to gain mechanistic understanding of how ecosystems respond to climate change. Establishing warming experiments is an integral part of this quest for knowledge. Many methods exist to increase temperatures, some of which use energy from the environment (passive warming) while others rely on electric power (active warming). We discuss strengths and weaknesses of each of the methods, also focusing on recent improvements. Passive warming methods are generally less costly and require less technological know-how compared to active methods, but this comes at the expense of control over the achieved temperatures. Active warming methods provide more control, but their reliance on electric power limits their use in remote locations. Weaknesses differ among the methods: asymmetric warming, unwanted co-occurring changes in other environmental variables, disturbances, etc. No warming method is free of flaws, yet every method also has distinct advantages. The fact that strengths and weaknesses differ among the methods also implies that researchers can pick the most optimal method for their specific experiment. This would avoid mismatches between the warming method and the study at hand and should thus lower the chances of conclusions being skewed by experimental artifacts.