Warm IRAC [3.6] and [4.5] photometry is critical for understanding the cold population of brown dwarfs now being found, objects which have more in common with planets than stars. As effective temperature drops from 800K to 400K, the fraction of flux emitted beyond 3um increases rapidly, from about 40% to >75%. This rapid increase makes a color like H-[4.5] a very sensitive temperature indicator, and it can be combined with a gravity and metallicity sensitive color like H-K to constrain all three of these fundamental properties - temperature, gravity and metallicity - which in turn gives us mass and age for these, generally isolated, slowly cooling objects. Our goal is to accurately characterise the temperature/ gravity/ metallicity distribution of the coolest brown dwarfs being found in the UKIRT Infrared Deep Sky Survey (UKIDSS) and the Visible and Infrared Survey Telescope for Astronomy (VISTA), which is only possible if IRAC photometry is available to complement our near-infrared data. While data at similar wavelengths will be provided by WISE for a sample of brown dwarfs, there are large differences between the photometric systems, which will be dependent on metallicity, gravity and the degree of turbulent mixing. Hence to fully exploit the sample of cold T dwarfs found by the near- and mid-infrared sky surveys, and to provide a homogeneous dataset for all ultracool dwarfs, a large number of sources must be observed in both the IRAC and WISE filter sets. Furthermore, different populations will be identified by the different surveys, and the number of cold brown dwarfs will be small, hence IRAC follow- up of UKIDSS, VISTA and WISE brown dwarfs is extremely valuable. The Cycle 8 time will increase the number of 400-600K near-infrared-selected brown dwarf (a sample with mass 5-20 M_Jupiter) that have IRAC data to ~25, a significant increase of ~50%. We expect to trigger eleven low impact ToO observations during Cycle 8, totalling 9.9 hours of AORs.