If you've read a TCFD report, you've probably run into a string of letters and numbers like "SSP2-4.5" and felt your eyes glaze over. While the terminology can be confusing, these numbers are linked to five pretty useful climate scenarios, developed by the world's leading climate scientists and economists, that have been put together with a level of scientific rigor that's easy to miss under all the acronyms. While they aren’t an immediate part of my work on a day-to-day basis, throughout my academic and professional life, I’ve found the IPCC’s five climate scenarios to be an immensely useful framing for different versions of how the future could unfold. After a recent bit of brushing up, let’s unpack them together.
The Intergovernmental Panel on Climate Change (IPCC) is the United Nations body that periodically reviews and summarizes the state of climate science. It doesn't run its own experiments or generate new data, but its job is to pull together the work of thousands of scientists across hundreds of climate models and distill it into a small number of reports that policymakers, businesses, and the public can more practically use. The most recent of these, the Sixth Assessment Report (AR6), came out in 2021–2022, and it's the source of the five scenarios commonly used today.
A climate scenario is a "what if," or a hypothetical story about how the world might develop, paired with the emissions trajectory that story would produce. There's no scenario the IPCC recommends or is rooting for; each one is a lens for stress-testing a plan, a portfolio, or a business against a different version of the future.
Each of the five headline scenarios pairs two things:
For example, the "SSP5-8.5" is the SSP5 storyline paired with a pathway that reaches 8.5 W/m² of additional forcing by 2100. The higher the number, the hotter the outcome.
Scenarios give us a central, "most likely" estimate of future warming, but also a wider range around it. Climate scientists pay attention to the extremes of that range the same way you'd buy insurance against a house fire even though it's unlikely. Comparing scenarios is a way of seeing how much the range of our future depends on the choices we make starting now.
SSP1-1.9 — 1.4°C by 2100. Global CO2 emissions hit net zero by around 2050. Societies pivot away from growth-at-all-costs and toward wellbeing, with real investment in education and health. This is the pathway most consistent with the Paris Agreement's 1.5°C goal and, as of the most recent independent tracking, it's also the farthest from where the world is currently headed (more on that below).
SSP1-2.6 — 1.8°C by 2100. The same optimistic, wellbeing-focused world as SSP1-1.9, just moving a little slower. Emissions still fall severely, but net zero doesn't arrive until sometime after 2050.
SSP2-4.5 — 2.7°C by 2100. No dramatic shifts in either direction. Historical social and economic trends continue roughly as they have been. Emissions hover near current levels before starting to decline around mid-century but never reach net zero by 2100. Progress happens unevenly and not fast enough.
SSP3-7.0 — 3.6°C by 2100. Nationalism resurges, international cooperation frays, and countries turn inward to prioritize their own security and food supply. Climate action slides down the priority list. Emissions roughly double by 2100.
SSP5-8.5 — 4.4°C by 2100. The highest-emissions pathway: rapid, energy-intensive economic growth built on continued fossil fuel expansion. Global CO2 emissions roughly double by mid-century.
Why isn’t there an SSP4? There is, technically — SSP4 describes a world of widening inequality within and between countries.The four combinations picked by the IPCC already span the full range of plausible outcomes, and they line up with the prior generation's RCP scenarios for easy comparison. SSP1-1.9 was added on top of that because of its direct relevance to the Paris Agreement. SSP4 combinations exist and get used in research, but they never got promoted to headline status.
Is SSP5-8.5 "business as usual"? No, and this is one of the most persistent assumptions that come up. SSP5-8.5 was deliberately built as a high-end, bounding case. Even when it was created, it sat at the very top of existing "no new policy" projections. Since then, the plunging cost of wind and solar and a decade of new climate policy have made it look increasingly implausible, though it remains a legitimate stress-test for the upper bound of physical risk.
When I first learned about the climate scenarios, the first question on my mind was: which of these are we actually on pace for? The most recent independent analysis puts the world's current policies on track for about 2.6°C of warming by 2100, or essentially right in line with SSP2-4.5, the "middle of the road" scenario. Countries' formal pledges and targets, if every one of them were fully met, would bring that down to roughly 2.2°C. The most optimistic case (every net-zero target hit, on time) lands around 1.9°C, which is still short of the 1.5°C pathway that SSP1-1.9 describes. In short, the two "best case" scenarios remain aspirational.
IPCC scenarios are the reference point nearly every climate disclosure framework points back to — TCFD, IFRS S2, CSRD, you name it. When you see a company describe its exposure "under a 1.5°C scenario" or "under a 3°C scenario," there's a very good chance an SSP pathway sits underneath that language. Using the shared benchmark allows a bank, a regulator, an insurer, and a corporate sustainability team all to describe risk against the same yardstick.
What I find most beautiful (and frightening) about these scenarios is the holistic picture they can paint for a warming world. Seeing SSP1's shift toward wellbeing and education sit right alongside its 1.5°C outcome, or SSP3's retreat into nationalism and rivalry sit alongside a hotter, harsher one, makes the quantification of climate change and the way we choose to live together into one story. While the SSP5-8.5 scenario is a scary one to sit with, that intersection of humans and our environment is impossible to ignore, and sometimes that's exactly what regulators, investors, business leaders, strategists, communicators, and others need to connect the dots between climate and how it affects our world.
Because IPCC scenarios are the framework most of our clients' peers, investors, and regulators already recognize, we often lean on them to ground the physical-climate side of a climate risk assessment and what a given level of global warming actually means for temperature, precipitation, sea-level rise, and extreme weather in the places our clients operate. Where it gets more interesting is translating that physical story into something a business can plan against — what a given warming pathway means for a company's costs, permitting environment, customer demand, and balance sheet. That's where we also rely on external frameworks like the NGFS (Network for Greening the Financial System) to help our clients translate those global pathways into the financial and strategic terms a business can plan around.
Sources:
MIT Climate Portal — Climate Scenarios Explained
UCAR/SciEd — Compare IPCC Scenarios
Reuters — UN climate report's five futures, decoded
Carbon Brief — CMIP6 explained; DKRZ — The SSP Scenarios
Climate Action Tracker — Warming Projections Global Update, November 2025
Climate Action Tracker — CAT Thermometer
Shara is a Senior Strategist at thinkPARALLAX with a decade of cross-functional experience across energy, climate, food systems, and technology. Her client experience includes leading brands such as Panera, Campbell's, Ferrara, Snap, and Dematic, where she helps companies translate complex science, sustainability strategy, and business performance into stories that resonate. She believes lasting change is driven from within and that the right narrative can help companies build momentum and unlock value for the betterment of all.