The IPCC compiles scientific insights on climate change, informing policymakers and the public about risks and possible actions. One of its core tools is the use of future scenarios. Climate models and climate impact studies use emission scenarios—estimates of potential future changes in heat-trapping emissions—to help us see how choices made about emissions today can shape tomorrow’s climate. If you live in a coastal zone and have looked at maps of future sea level rise or have read about how climate change could be slowed with policy changes to reduce emissions, you’ve likely seen these scenarios in action. In essence, combined with climate models, they provide a way to envision the consequences of different actions or inactions.
Scenarios used in the IPCC are often mentioned in discussions about national climate targets, corporate sustainability plans, extreme weather events, slow onset events like sea level rise, and climate litigation. But what exactly are emission scenarios, how are they structured, and why are they essential for understanding climate change impacts and mitigation strategies?
What Are Future Climate Scenarios?
Scenarios are projections of future human-caused emissions and their effects on the Earth’s climate system. These scenarios are not predictions; they are “what-if” frameworks that allow us to test the likely outcomes of various choices and actions. By examining possible trajectories for global economic development, technology adoption, and policy actions, the driving forces behind emissions, these scenarios help us assess a range of potential climate futures.
How Scenarios Have Evolved
Over the years, the IPCC and the scientific community has refined how it develops these scenarios. Initially it used four different emission storylines from the Special Report on Emissions Scenarios (SRES) as a scientific basis, however, recognizing the need for a more flexible and policy-relevant framework, scientists developed the Representative Concentration Pathways (RCPs) for the IPCC reports. Four RCP scenarios describe different levels of radiative forcing in the atmosphere by 2100. Radiative forcing is the change in energy balance in the Earth’s atmosphere due to heat trapping emissions. The use of radiative forcing to understand emissions trajectories was then paired with varied political pathways to generate Shared Socioeconomic Pathways (SSPs).
The IPCC currently uses five SSPs that represent different ways society could evolve, incorporating everything from energy use to policy decisions that shape the climate future we may experience. These pathways describe different global socioeconomic conditions (e.g., levels of cooperation or competition among countries, technology adoption, and inequality) in terms of radiative forcing. The five shared socioeconomic pathways are:
- SSP1: Taking the green road– A world focused on sustainable development, global cooperation, and green technology adoption. This scenario would lead to the least amount of global warming.
- SSP2: Middle of the road – A scenario where global trends continue along historical patterns, with moderate development and emissions reductions.
- SSP3: A rocky road – A fragmented world with regional conflicts, slow economic growth, and high inequality, leading to continued high emissions.
- SSP4: A divided world – A highly unequal world where some adopt clean technology while much of the population remains dependent on fossil fuels.
- SSP5: Taking the highway – A scenario driven by economic growth and high fossil fuel use, leading to rapid warming.
These scenarios are identified by their social pathway and the approximate level of radiative forcing resulting from the scenario by 2100.
Figure 1: Future annual CO2 emissions in the five illustrative scenarios
By combining radiative forcing (the climate side, represented by the numbers at the end of each scenario name e.g. 1.9 and 8.5) with socioeconomic factors, SSP scenarios provide a richer description of how the world might develop and how that development would influence emissions.
How Do IPCC Scenarios Inform Climate Research?
IPCC scenarios serve as foundational tools in climate research, enabling scientists to explore how different concentrations of heat-trapping emissions influence global temperatures, sea level rise, extreme weather events, and broader environmental changes. These scenarios are used in climate models to simulate various outcomes based on emissions trajectories, helping researchers assess climate system responses to different forcings.
One of the primary applications of IPCC scenarios is in global climate modeling. Climate scientists run general circulation models (GCMs) with these scenarios to simulate future climate states under these different emissions pathways. Studies show that high-emission scenarios like SSP5-8.5 lead to significant disruptions in atmospheric circulation patterns, affecting monsoons and mid-latitude storm tracks, compared to the low-emissions scenario SSP1-2.6.
IPCC scenarios also help scientists evaluate changes in the intensity and frequency of events like hurricanes, droughts, and wildfires. A recent review of tropical cyclone studies found that under high-emissions scenarios (SSP5-8.5), storms become more intense and produce heavier rainfall—even if their overall global frequency decreases. Lower-emission scenarios (SSP1-2.6) show more moderate increases, underscoring how different policy choices alter storm behavior.
These scenarios can also reveal how forests, oceans, and other natural systems might absorb or release carbon in the future. Research published in Earth System Science Data examined how under high-emission scenarios (SSP5-8.5), the ability of forests and oceans to absorb CO₂ weakens. Meanwhile, an intermediate scenario (SSP2-4.5) shows these natural “carbon sinks” remaining more effective for longer.
These are just a few examples of how researchers use these scenarios to help us understand possible climate futures.
Why Understanding These Scenarios Matters
These scenarios illustrate the range of potential climate outcomes based on different emissions trajectories, helping to assess the impact of various policy choices. A world limited to 1.5°C warming contrasts sharply with a high-emissions path. Without these scenarios, it would be nearly impossible to quantify the consequences of different emissions pathways or evaluate which strategies might work best to address climate change. These scenarios provide more than just hypothetical futures; they are tools for informed decision-making. They allow researchers, policymakers, and the public to grasp the potential consequences of inaction versus proactive climate strategies.
As we navigate the challenges of climate change, these scenarios remind us that the future remains open—and that our collective actions today will determine the climate reality we pass on to future generations.