The five buttons are Shared Socioeconomic Pathways (SSPs) from the IPCC's Sixth Assessment Report — narratives about future population, economic growth and energy choices, each paired with an approximate 2100 radiative forcing target (the number in the name, in W/m²). SSP1-1.9 assumes rapid decarbonisation and net-negative emissions after mid-century; SSP5-8.5 assumes continued fossil-fuel-intensive growth with no new climate policy. Moving the year slider walks a precomputed trajectory (interpolated from published AR6 central estimates) for CO₂ emissions, atmospheric CO₂ concentration and global mean temperature anomaly for whichever scenario is selected.
ΔT(t) ≈ ΔT_2020 + (ECS/3.0) · [ΔT_scenario(t) − ΔT_2020]
ice_extent(t) ∝ max(0, 1 − k·max(0, ΔT(t) − 1.1°C))
- SSP1-1.9 / SSP1-2.6 — sustainability-first pathways; emissions fall to net-zero and beyond, keeping warming near or just above 1.5–1.8°C by 2100.
- SSP2-4.5 — "middle of the road": emissions plateau and only slowly decline, warming reaches roughly 2.7°C.
- SSP3-7.0 — regional rivalry, weak climate policy; emissions keep rising most of the century, warming near 3.6°C.
- SSP5-8.5 — fossil-fuelled development; the highest-emissions pathway, warming approaching 4.4°C by 2100.
- Climate sensitivity (ECS) — the equilibrium warming per doubling of CO₂; the default 3.0°C is the AR6 best estimate, but the true value is uncertain (likely range 2.5–4.0°C), which is why every scenario carries a warming range, not a single number.
The globe's ocean tint, the shrinking polar ice caps and the CO₂ haze density all respond live to the same numbers driving the graph, so a policy-relevant question — "what does 3°C of warming actually look like by 2100?" — has a visual, not just numerical, answer.