The Arctic is especially vulnerable to climate change and is warming faster than the global average. Changes in this region pose a serious threat to the future of the planet due to the immense amount of methane and carbon dioxide frozen as organic material in the soil. If the frozen soil (i.e., permafrost) were to melt, it would release these gases into the atmosphere, leading to further warming. Permafrost thaw can also result in infrastructure damage that impacts many Arctic populations, and can disrupt the hunter-gatherer lifestyle many Arctic Indigenous Peoples rely on. A better understanding of potential changes and uncertainties in permafrost melt will inform climate adaptation or mitigation plans needed to prevent serious harm. This research project investigated projected changes in 21st century Earth system model simulations, based on a scenario of continued reliance on fossil fuels (RCP8.5). The study assessed changes to Arctic permafrost and focused on simulations from the National Center for Atmospheric Research’s Community Earth System Model Large Ensemble experiment. We found that the vast majority of Arctic permafrost is completely lost by the end of the 21st century, but the exact timing varies across regions, and with soil depth. Natural variability plays a significant role in the timing of this melt, with a 10-20 year standard deviation in melt timing across most of the Arctic.