Global warming will have a destabilizing impact on society. Therefore, predicting future temperature increase is crucial. This can be done by studying trees as they are sensors of their environment, and they store this data in their rings: wide and small rings indicate varying growing conditions. Since trees register climate already far earlier than humans did, these ‘treemometers’ are key witnesses of global warming. Rings of ancient bristlecone pines from Southwest USA, the oldest trees in the world, were used for temperature reconstructions, that led to the famous ‘hockey stick’ graph, showing dramatically increased temperatures during the last decades. Maximum Latewood Density (MXD), the density of the heaviest wood cells measured at the end of each ring, is a better predictor of temperature than ring width but has not yet been recorded for bristlecone pine because it is hard to measure. In this project, I will generate the first temperature reconstruction based on MXD of bristlecone pine using a set of high-tech tools. MXD and other density data will be examined in tandem with novel records such as elemental content of tree rings. The multi-millennial record from these ancient trees thus puts current climate change in the context of changes in the past. Data generated from this project will thus make climate predictions more accurate, which is more urgent than ever.