Greenhouse Effect & Climate Lab

About this model

A model, not the real atmosphere. The planet is one global average: one surface temperature, one layer of atmosphere, a two-layer ocean. Real climate models split Earth into millions of boxes. This one keeps the physics you can test and check.

Energy in. Sunlight at Earth is 1361 W/m² (Kopp & Lean 2011). Spread over the whole sphere that is 1361 ÷ 4 ≈ 340 W/m². Earth reflects about 30 % (its albedo, 0.30; CERES satellite measurements), so it absorbs about 238 W/m².

Energy out. The surface gives off infrared by the Stefan–Boltzmann law, σT⁴ (σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴). The atmosphere is one layer that absorbs a fraction ε of that infrared and sends half back down and half out to space, so infrared to space = (1 − ε/2)·σT⁴. With no atmosphere (ε = 0) Earth would settle at 255 K (−18 °C); with the pre-industrial atmosphere it settles at 287 K (14 °C), about 33 °C warmer: the natural greenhouse effect. In this one-layer model the back-radiation is about 150 W/m²; the real value (≈ 340 W/m²) is larger because the real atmosphere also absorbs sunlight and is heated by rising warm, moist air.

Greenhouse gases. ε rises with the radiative forcing of the gases, from the IPCC formulas (Myhre et al. 1998): CO₂ ΔF = 5.35 · ln(C/280), so doubling CO₂ gives 3.7 W/m²; methane and nitrous oxide use the IPCC square-root formulas with their overlap term. Other gases (CFCs, ozone) are left out. ε also rises with temperature, standing in for the water-vapour feedback (warmer air holds about 7 % more water vapour per °C).

Climate sensitivity. The model is tuned so that doubling CO₂ eventually warms Earth by 3 °C, the IPCC AR6 best estimate (likely range 2.5–4 °C). AP students can change it in Advanced. The ice–albedo feedback is explicit (AR6: +0.35 W/m² per °C); switching it off gives about 2.3 °C per doubling.

Surfaces and clouds. Albedo values are single picks inside published ranges (Oke 1987; Hartmann 2016): open ocean 0.06 (0.03–0.10), sea ice 0.70 (0.50–0.85), fresh snow and ice sheets 0.85 (0.75–0.95), forest 0.15 (0.08–0.20), grassland 0.25 (0.16–0.26), desert 0.35 (0.30–0.45), city 0.15 (0.10–0.27). Clouds (today about 67 % cover) reflect sunlight (about −44 W/m²) and absorb infrared (about +28 W/m²), so overall they cool. These are simple linear estimates matched to satellite (CERES) values. Real cloud feedback is the largest uncertainty in climate sensitivity.

Aerosols. Haze from pollution reflects sunlight. The “Today” atmosphere includes the IPCC AR6 estimate of −1.1 W/m² (range −1.7 to −0.4).

Time and the ocean. The surface and upper ocean warm quickly; the deep ocean takes centuries (a two-layer ocean model, Held et al. 2010, with CMIP5 average values from Geoffroy et al. 2013). That is why warming continues after CO₂ stops rising. One second of Play at 1× is 2 model years.

Gas tube. A 1 m tube at 1 atmosphere and a 100 °C infrared lamp, like John Tyndall’s 1859 experiments. The percentages absorbed are illustrative estimates from where each gas absorbs in the infrared, not laboratory measurements. The pattern is real: molecules with 3 or more atoms (CO₂, CH₄, N₂O, H₂O) absorb infrared; N₂, O₂ and Ar don’t; none absorbs visible light. The bands saturate, so doubling the gas does not double the absorption (why forcing grows with the logarithm of CO₂). Detector noise is from a seeded random generator: the same seed repeats the same readings.

Real data, stored in the page. Mauna Loa monthly CO₂, March 1958–September 2026 (NOAA Global Monitoring Laboratory; Scripps Institution of Oceanography before 1974). Antarctic ice-core CO₂ composite over 800,000 years (Bereiter et al. 2015) and EPICA Dome C temperature (Jouzel et al. 2007), both averaged into 2,000-year steps. The ice-core temperature is for Antarctica, which swings about twice as much as the global average. Global temperature anomalies, 1880–2025 (NASA GISTEMP v4, vs 1951–1980).

Molecule counts and photon packets are drawn to show the idea, not to scale: 10 CO₂ molecules stand for 280 ppm, and packet numbers follow the model's energy flows.

IPCC AR6 WG1 · NOAA GML: CO₂ trends · NOAA paleo: ice-core CO₂ · EPICA Dome C temperature · NASA GISTEMP · NASA CERES · NASA: Earth's energy budget

What am I looking at?

How the lab works. Pick Explore or one lab at the top. Each lab has five tabs: Pre-lab, Bench, Data & graph, Claim · Evidence · Reasoning, and Test. On the Bench, the coach on the right lists your steps; they tick themselves as you work. Press What do I do now? when you're stuck.

① Planet. A slice of Earth from space down to the ground. Sunlight is a short yellow packet with a sun icon; infrared (heat) is a longer, wavier red packet with a flame icon. Sunlight comes in from the Sun at the top left. Some bounces off clouds, air and bright ground; the rest is absorbed and warms the surface (it glows orange). The warm surface sends infrared up. Greenhouse-gas molecules catch some of it, vibrate, and send it off in a random direction: up to space or back down. Tap a molecule, cloud or patch of ground to name it. On the right, the balance compares energy in (absorbed sunlight) with energy out (infrared to space) and tips when they differ; the thermometer shows the surface temperature and, dashed, where it will settle. Press Play to run the climate clock (2 years per second at 1×), Follow a photon to trace one infrared packet, and zoom with ＋ / －, Z / X, scroll or pinch.

② Gas tube. An infrared lamp shines through a 1 m glass tube onto a thermopile detector; the meter shows how much gets through. Choose a gas, the lamp and how far the valve is open, then Measure. The close-up shows whether the molecule vibrates when infrared hits it.

③ Data wall. Real measurements: the Keeling curve, the 800,000-year ice core and the global temperature record. Tap a small screen to bring it to the big one, Replay to watch it draw, and tap or hover over the big screen to read a value.

Advanced (under the controls) has nitrous oxide, aerosol haze, the climate-sensitivity setting and the instrument seed.

Keys: Space play / pause · → step · R reset · Z / X zoom (planet view).