The year 2100 serves as a projected benchmark for assessing the long-term consequences of current global trends, particularly those related to climate change and human development. Projections from scientific bodies, such as the Intergovernmental Panel on Climate Change (IPCC), utilize various scenarios to model the Earth’s future state, accounting for different levels of global cooperation and greenhouse gas emissions. These models explore the physical transformation of the planet, the resulting ecological changes, the shifting dynamics of human society, and the technological responses required to sustain civilization.
The Global Climate and Physical Landscape
Projected temperature increases by 2100 vary dramatically, depending on the success in curbing greenhouse gas emissions. Under a very low emissions scenario (net-zero CO2 around 2050), the global average temperature rise is projected to be contained to around 1.8°C compared to pre-industrial levels. Conversely, a very high emissions scenario (doubling current CO2 emissions by 2050) could result in a temperature increase of 4.4°C by the end of the century. A “middle-of-the-road” scenario, assuming current socio-economic trends continue, projects a temperature rise of 2.7°C.
Global mean sea level rise is an inevitable consequence of warming, projected to continue for centuries even with deep emissions reductions. By 2100, the likely range of increase is between 0.28 and 1.01 meters (0.9 to 3.3 feet) under various scenarios. The lowest range is associated with the most optimistic emissions pathway, while the higher end aligns with high-emissions scenarios. A low-likelihood, high-impact scenario involving rapid ice sheet collapse could potentially push the rise close to 2 meters by 2100.
The intensification of the water cycle is a significant physical change, leading to more intense rainfall and associated flooding in many regions. At the same time, the contrast between wet and dry regions is expected to become greater. High latitudes are likely to see increased precipitation, while large parts of the subtropics are projected to experience a decrease.
Changes in atmospheric circulation will intensify extreme weather events, making them more frequent and severe. Hot extremes, including heatwaves, are virtually certain to increase, alongside a greater proportion of intense tropical cyclones. Agricultural and ecological droughts are projected to become more severe in many regions, including North and South America, the Mediterranean, and Eurasia. Compound events, such as concurrent heatwaves and droughts, are expected to increase in nearly all land regions.
Biodiversity Loss and Ecosystem Shifts
The physical changes in temperature and precipitation will drive a significant decline in global biodiversity by 2100. If current trends continue, some models suggest that the Earth could lose more than a tenth of its plant and animal species by the end of the century. Under the most severe warming scenarios, the loss could reach up to 27% of all species.
Species losses are amplified by “co-extinctions,” where the disappearance of one species triggers the loss of others that depend on it. The interconnectedness of food webs means that the actual rate of extinction for the most vulnerable species could be significantly higher than projections based on direct climate effects alone.
Marine ecosystems face particularly severe consequences from both warming and ocean acidification. As the ocean absorbs atmospheric CO2, its pH decreases, which erodes the calcium carbonate structures of organisms like corals. Rising sea surface temperatures and increasingly acidic waters could eliminate nearly all existing coral reef habitats by 2100.
The loss of coral reefs represents habitat loss, threatening a large amount of the ocean’s biodiversity. Beyond the reefs, changes in temperature and water availability will cause major shifts in terrestrial biome distribution. Desertification is expected to expand in certain regions, while other biomes will migrate poleward or to higher altitudes, altering ecosystem function. The loss of these stable ecosystems also compromises services like pollination and water purification, important for human well-being.
Human Population and Settlement Dynamics
Global population size is projected to peak within the current century, with an estimated likelihood of 80% that the peak will occur between the mid-2060s and 2100. The world’s population in 2100 is expected to be approximately 700 million people fewer than earlier estimates, due to lower-than-anticipated fertility rates in several large countries. Despite this eventual peak, certain regions, particularly those in sub-Saharan Africa, are expected to see significant population increases, with the continent’s population potentially reaching 3.3 billion by the century’s end.
The 21st century will see a shift in urbanization, characterized by the rise of new mega-cities, defined as urban areas with populations exceeding 10 million. Projections indicate that the world’s largest cities will be concentrated primarily in Africa and Asia. Cities like Lagos, Kinshasa, and Dar es Salaam are expected to experience rapid growth, potentially surpassing 60 million inhabitants each. This demographic shift is fueled by high birth rates and rural-to-urban migration.
Climate-driven migration will fundamentally reshape settlement patterns, forcing millions of people to relocate. People living in coastal areas that are frequently inundated are assumed to migrate, resulting in a net land loss ranging from 2,800 to 490,000 square kilometers globally over the century. Across the range of sea-level rise scenarios, an estimated 4 million to 72 million people could be displaced internationally and internally by 2100.
This rapid urbanization and climate-driven displacement will place infrastructure strains on densely populated, vulnerable areas. Coastal cities, which are often economic hubs, face the dual challenge of accommodating population growth while simultaneously protecting infrastructure from increasing coastal flooding and erosion caused by sea-level rise. The capacity of these urban centers to provide basic services like clean water and housing will be a defining challenge of the coming decades.
Energy Transition and Resource Management
The shift in the global energy mix is a defining feature of the 2100 projection, driven by the necessity to phase out fossil fuels to limit warming. In Paris Agreement scenarios, renewable energy sources like solar and wind would need to become the dominant sources of power, increasing their proportion of the total global energy mix from today’s 15–20% to as high as 60–80% by 2050. However, total global energy demand could grow significantly, potentially increasing by 124% by 2100 due to population and economic growth.
Global water scarcity will worsen due to climate change and socio-economic factors. Up to 66% of the global population is projected to experience clean water scarcity by the end of the century, particularly in the Global South. Addressing this requires integrated water management techniques, including widespread treatment and reuse of wastewater, and implementing water-saving methods in agriculture, which accounts for about 70% of global freshwater use.
Future food production systems will rely on technological innovation to feed a large, increasingly urbanized population while dealing with water scarcity and reduced arable land. Controlled-environment agriculture (CEA) is expected to play a role, with vertical farming allowing for crop production year-round, independent of weather, in climate-controlled indoor facilities. Vertical farming uses up to 95% less water than traditional farming and eliminates the need for pesticides.
Beyond conventional crops, the food system will likely incorporate alternative protein sources. Synthetic proteins, alongside insect-based foods and cultivated meat, offer a way to deliver high protein yields with a reduced environmental footprint compared to traditional livestock. These systems also support circular economy models by being able to process crop waste into edible protein, thereby addressing the need for both food security and efficient resource use.