As the temperature of a sample of hydrogen gas increases, electrons in the atoms gain more energy, on average, per second from collisions with other hydrogen atoms. This excites the electrons more often, making it more likely for any given electron to be in the n=2 level at any given time. More Balmer photons can be absorbed per second, the overall intensity of a Balmer wavelength reaching the Earth decreases, and the intensity of the Balmer lines increase