At a time in the near future, many computers (including devices such as smart-phones) will have system clocks that are synchronized to a high degree (less than 1 ms of error). This will enable us to coordinate events across unconnected devices with a degree of accuracy that was previously impossible. In particular, high clock synchronization means that we can use these clocks to synchronize tempo between humans or sequencers with little-to-no communication between the devices. To facilitate this low-overhead tempo synchronization, we propose the Global Metronome, which is a simple, computationally cheap method to obtain absolute tempo synchronization. We present experimental results demonstrating the effectiveness of using the Global Metronome and compare the performance to MIDI clock sync, a common synchronization method. Finally, we present an open source implementation of a Global Metronome server using a GPS-connected Raspberry Pi that can be built for under $100.