A tissue ablation system comprising: a microwave ablation device (120a, 120b, 120c) configured to provide energy to a target area and configured to cause ablation by emission of microwave energy; an ablation generator configured to provide power to the ablation device; and a controller in communication with the ablation generator and being configured to: cause the ablation generator to apply a first power level to the ablation device at a first time; and cause the ablation generator to apply a second power level to the ablation device at a second time, the second power level being higher than the first power level and the second time being after the first time; wherein the power provided by the ablation generator to the ablation device is adjustable from the first power level to the second power level between the first time and the second time, adjusting the power from the first power level to the second power level comprises causing the ablation generator to provide a plurality of distinct intermediate power levels corresponding to delivering a plurality of intermediate energy levels from the ablation device to the target area, and each of the intermediate power levels is between the first power level and the second power level, and each consecutive intermediate power level is greater than the previous intermediate power level, wherein each intermediate power level is between 1 W and 10 W greater than the previous intermediate power level and wherein a time between the first time and the second time is between 40 seconds and 100 seconds. a microwave ablation device (120a, 120b, 120c) configured to provide energy to a target area and configured to cause ablation by emission of microwave energy; an ablation generator configured to provide power to the ablation device; and a controller in communication with the ablation generator and being configured to: cause the ablation generator to apply a first power level to the ablation device at a first time; and cause the ablation generator to apply a second power level to the ablation device at a second time, the second power level being higher than the first power level and the second time being after the first time; wherein the power provided by the ablation generator to the ablation device is adjustable from the first power level to the second power level between the first time and the second time, adjusting the power from the first power level to the second power level comprises causing the ablation generator to provide a plurality of distinct intermediate power levels corresponding to delivering a plurality of intermediate energy levels from the ablation device to the target area, and each of the intermediate power levels is between the first power level and the second power level, and each consecutive intermediate power level is greater than the previous intermediate power level, wherein each intermediate power level is between 1 W and 10 W greater than the previous intermediate power level and wherein a time between the first time and the second time is between 40 seconds and 100 seconds. cause the ablation generator to apply a first power level to the ablation device at a first time; and cause the ablation generator to apply a second power level to the ablation device at a second time, the second power level being higher than the first power level and the second time being after the first time; wherein the power provided by the ablation generator to the ablation device is adjustable from the first power level to the second power level between the first time and the second time, adjusting the power from the first power level to the second power level comprises causing the ablation generator to provide a plurality of distinct intermediate power levels corresponding to delivering a plurality of intermediate energy levels from the ablation device to the target area, and each of the intermediate power levels is between the first power level and the second power level, and each consecutive intermediate power level is greater than the previous intermediate power level, wherein each intermediate power level is between 1 W and 10 W greater than the previous intermediate power level and wherein a time between the first time and the second time is between 40 seconds and 100 seconds.