Climate Scenarios vs. Climate Projections: What’s the Difference?

When discussing climate change, two terms often come up: climate scenarios and climate projections. But what exactly sets them apart? Are scientists predicting the future, or are they modeling possible outcomes?

Climate Scenarios: Socio-Economic Assumptions

A climate scenario is not a forecast—it’s a hypothesis. It outlines different possible pathways our societies might follow. Each scenario sets specific values for key parameters—such as greenhouse gas emissions—based on different combinations of economic, technological, political, and social decisions.

Today, the Intergovernmental Panel on Climate Change (IPCC) uses Shared Socioeconomic Pathways (SSPs) to illustrate a range of possible global futures depending on our collective choices. Here are three examples:

• SSP1-1.9: A sustainability-focused future, where global cooperation helps limit global warming to 1.5°C.
• SSP2-4.5: A “middle-of-the-road” pathway, continuing current trends without significant policy or technological change. The Paris Agreement goals are not met.
• SSP5-8.5 : A world driven by fossil fuel-based growth, where emissions continue to rise sharply, leading to extreme warming. The Paris targets are surpassed around 2040.

Each scenario combines a socio-economic narrative (SSP) with an associated level of greenhouse gas emissions. These scenarios form the starting point, or input data, for climate models.

In short: Scenarios set the stage.

Climate Projections: Scientific Simulations

A climate projection is a scientific simulation—it describes how the climate would respond under the conditions laid out in a particular scenario. Unlike scenarios, projections are not influenced by societal choices; they are based on the laws of physics.

Projections come from complex climate models that take into account:

• The movement of air and ocean currents
• Exchanges of energy and matter between the atmosphere, oceans, ice, soil, and ecosystems
• Climate feedback loops—for example, shrinking snow cover that accelerates warming, or changes in how the ocean absorbs carbon dioxide

Since the 1970s, climate models have incorporated an increasing number of variables.

They are grounded in robust scientific equations drawn from thermodynamics, fluid dynamics, and atmospheric chemistry. These models help translate human actions into data on future climate outcomes. The projections they produce—such as the projected average global temperature by the end of the century—are the outputs of these models.

In short: Projections turn assumptions into concrete climate outcomes.

Rigorous Science—Not Speculation

Understanding the difference between scenarios and projections is key to grasping what climate science can—and cannot—tell us about the future.

Scientists do not claim to predict what will happen. Instead, they explore a range of plausible futures, based on the decisions we make today. Their work is rooted in rigorous scientific methodology, not speculation.

So the question isn’t: “What’s going to happen?” But rather: “What future do we want to create?”