Much of the understanding of the linkages between human-caused emissions of greenhouse gases and other anthropogenic climate changes is based on complex climate models that have generally performed well in tracking current global temperatures. Nonetheless, these models are approximations (albeit very sophisticated ones) that cumulate several possible sources of errors. This chapter will discuss in general terms the current scientific state of understanding of the direction and scope of climate change and how these changes may give rise to transport infrastructure or network service-damaging hazards. It also addresses the extent with which confidence can or should be ascribed to projections of future hazards such as temperature change, sea level rise, changes in precipitation, etc.