Definitions: Temperature signal: A change in photosynthesis or respiration solelyattributable to changes in temperature, i.e., the signal excludes otherclimatic effects such as water availability and sunlight. Tipping point: This denotes the temperature threshold at which theglobal land surface will switch from a carbon sink to a carbon sourcewhen—due solely to temperature—photosynthesis is in exponentialdecline while respiration is in exponential increase. Thermal maxima: The thermal maximum (Tmax) represents the peak ofthe temperature dependence curve where any additional increase intemperature will decrease the metabolic rate of either photosynthesisor respiration. Warmest Quarter: Mean temperature of warmest quarter (3-monthperiod)