Projections of future numbers of people exposed to climate change-related hazards described in this chapter and elsewhere in this report are heavily influenced by assumptions about population change over time at global, regional and national scales. One challenge concerns global and regional variability of baseline data for current populations, which is typically aggregated from national censuses that vary considerably in terms of frequency, timing and reliability, especially in low-income countries. A number of gridded mapping dataset initiatives emerged in recent years to support population-environment modelling research at global and regional levels, common ones being the Gridded Population of the World, the Global Rural Urban Mapping Project, and LandScan Global Population dataset . For future population projections at national levels, researchers commonly draw upon data generated by the Population Division of the United Nations Department of Economic and Social Affairs, which publishes periodic projections for future fertility, mortality, and international migration rates for over 200 countries, the most recent projections being for the 2020 to 2100 period . There have been debates among demographers regarding the precision of DESA projections, and whether these overestimate or underestimate future population growth in some regions . Population growth rates are highly influenced by socioeconomic conditions, meaning that future population levels at local, national and regional scales are likely to respond to relative rates of progress towards meeting the Sustainable Development Goals . The Shared Socioeconomic Pathways  used in climate impacts and adaptation research include a variety of assumptions about future mortality, fertility and migration rates and provide a range of population growth scenarios that diverge after the year 2030 according to future development trajectories  and are then further modified and downscaled by researchers for national-level studies. Understanding future risks of climate change will benefit from continued efforts by the international community to collect and share data on observed population numbers and trends, and to work towards better projected data for population characteristics that strongly influence vulnerability to climate risks, such as gender, age and indigeneity.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report