Three realisations of the CMB temperature fluctuations caused by the GWM of a population of mergers. The merger events have a mass of M = 10⁹ M_⊙ and are drawn from a uniform distribution in space-time and inclination and orientation angles. As the number of mergers is increased according to a specified volumetric merger rate, ℛ, both the amplitude and the standard deviation of the temperature fluctuations grows following a random-walk scaling. The colour bars are adjusted to account for this behaviour. With sufficient sources within a box (∼10 or more), the temperature fluctuations tend to follow universal power spectrum with a scaling, ∝k^−2.7, where k are the modes.