The transitional zone between land and ocean is of profound importance for human and naturallife. Today, most coastal systems are strongly influenced by human construction and land usechange. A warming climate affects the entire planet, but coastal systems are especially exposed tothe impacts of climate change through rising sea levels and increased storminess. In Denmark, theanthropogenic influence on the coasts is high, creating a closely-linked interplay between naturaland anthropogenic driving factors of coastal change. Compared to Denmark, the anthropogenicinfluence on the coasts is much lower in Greenland, but the Arctic experiences a warming that isfaster than elsewhere in the world. The ongoing climate change enhances the coastal erosionpressure through increased rainfall, warmer sea surface temperatures and sea level rise. In theArctic, amplified precipitation in combination with thawing permafrost and melting ground iceleads to soil and surface sediment erosion. Warmer seas are increasing coastal erosion risks byreducing the time that sea ice protects the coast from wave action.Among coastal landforms, cliffs are globally understudied compared to other low lying coastalenvironments. Both in Denmark and Greenland, the drivers of soft sediment coastal cliff erosionare largely unknown. Denmark with its digitalized society and governmental agencies, offersdatasets for the natural and anthropogenic spheres on a high spatial resolution. However, mergingthose datasets remains challenging and understanding the driving factors of coastal cliff erosionrequires additionally a high temporal resolution. In Greenland, data about coastal change is sparseand knowledge about coastal cliff erosion hardly exist.This PhD thesis investigates the drivers of soft sediment coastal cliff erosion in Denmark andGreenland during the last decades and under a changing climate in the present and future. Paper 1explores a new smartphone based technique to measure coastal cliff erosion with a high temporalresolution. Paper 2 and 3 investigate (coastal) landslides in Denmark. Paper 4 investigates thedrivers of coastal cliff erosion and landslides in Denmark. In Paper 5, we measure coastal cliffretreat at a sedimentary cliff in Greenland and explore impacts of climate change, especially thelonger ice-free sea states on the dynamics of cliff failure.Newly developed LiDAR sensors built into smartphones allow cost-effective, fast and accuratereconstruction of cliff surfaces. This technique can be used to measure coastal change with a hightemporal resolution e.g. before and after storms. Along the Danish cliff coast that was coveredunder the Weichselian ice-sheet, landslides are common responses to hydrological and coastalprocesses and they deliver easily erodible sediments to the beaches and further into the nearshorezone. By mapping landslides along the coast of Denmark, we can distinguish between highfrequency, low magnitude cliff erosion processes and low frequency, high magnitude landslideevents. Coastal cliff morphology varies across Denmark with the highest and fastest eroding cliffsat the west coast and a higher number of coastal landslides eroding more irregularly at the inner-coastal waters. The natural and anthropogenic driving factors of cliff erosion are interrelated.Along the west coast, cliff erosion is largely wave-driven. At the fetch-limited coasts, land-use,hydrology and underlying geology are more pronounced driving factors of cliff erosion. InGreenland, eroding sedimentary coastal cliffs are unexplored. At those cliffs, fine sediment istransported downslope to the beach by surface runoff following precipitation events. During stormevents, waves running up to the cliff toe erode the fine sediment. Increased rainfall, more frequentstorms and less sea ice will lead to higher erosion rates in Greenland in the near future.