Greenhouse Effect Simulator
Equations in this simulation
| S₀ | Sunlight at the top of the atmosphere S₀ (W/m²) | the solar constant, 1,361 W/m²; divided by 4 because a sphere has four times the area of the disk it presents to the Sun | |
|---|---|---|---|
| α | Albedo α (fraction of sunlight reflected) | 0.30 for the Earth as a whole: clouds, ice and deserts reflect, oceans and forests absorb |
With the current values:
| T_e | temperature the Earth would have with no greenhouse effect | about 255 K (−18 °C); σ = 5.67 × 10⁻⁸ W/(m²·K⁴) |
|---|
With the current values:
| ε | fraction of the ground's infrared the atmosphere absorbs | about 0.77 in a one-layer model, which warms the surface to the observed 15 °C |
|---|
With the current values:
| C | Carbon dioxide (ppm) | 280 ppm before industry; each doubling adds 3.7 W/m² of forcing | |
|---|---|---|---|
| M | Methane (ppb) | 722 ppb before industry | |
| ΔF | radiative forcing | the extra energy per square meter the planet keeps, compared with the year 1750 |
With the current values:
| λ | climate sensitivity parameter | K per W/m²: 0.32 for the Planck response alone, about 0.8 with the water vapor, ice and cloud feedbacks | |
|---|---|---|---|
| C_h | heat capacity of the ocean's mixed layer | 8 W·year/(m²·K), so the temperature takes years to catch up with the forcing | |
| T | global average surface temperature | starts at the pre-industrial 13.8 °C and moves toward the new balance |
With the current values:
How to use the greenhouse effect simulator
- Yellow photons of sunlight come down; a share given by the albedo bounces straight back to space and the rest warms the ground. The ground sends red infrared photons up, and when one hits a carbon dioxide or methane molecule in the atmosphere it is absorbed and sent off in a random direction, often back down. That returned energy is the greenhouse effect.
- Raise the CO₂ and watch more infrared get caught. The radiative forcing jumps at once, but the temperature climbs over years as the ocean warms, until the outgoing energy balances the incoming again. The charts follow the temperature, the forcing and the energy still being gained; the main chart plots the warming at balance against CO₂ for each choice of feedbacks.
- Change the albedo to see what more ice or cloud does, or the Sun's output for its smaller effect, and pick the climate feedbacks to see how the same forcing gives 1.2 °C or 4.5 °C per doubling of CO₂. The Blackbody Radiation Simulator shows why the Sun shines in visible light and the Earth in infrared.
Frequently asked questions
What is the greenhouse effect?
Sunlight, mostly visible, passes through the atmosphere and warms the surface. The warm surface radiates infrared, and gases such as water vapor, carbon dioxide and methane absorb much of it and re-radiate it in all directions, including back down. The surface ends up about 33 °C warmer than it would be without them: 15 °C on average instead of −18 °C.
What is radiative forcing?
The change in the energy balance at the top of the atmosphere caused by something like extra CO₂, in watts per square meter. CO₂'s forcing grows with the logarithm of its concentration, ΔF = 5.35 ln(C ÷ 280): each doubling adds about 3.7 W/m². From 280 to 420 ppm it is about 2.2 W/m².
What is climate sensitivity?
The warming once the climate has settled after CO₂ doubles. With no feedbacks it would be about 1.2 °C. Warmer air holds more water vapor, itself a greenhouse gas, and melting ice darkens the surface, which roughly doubles or triples that; the likely range is 2.5 to 4 °C, with 3 °C the best estimate.
Why does the temperature lag behind the CO₂?
The oceans take up heat and warm slowly. This simulation's single mixed ocean layer catches up in a decade or so; the real deep ocean takes centuries, which is why the Earth has warmed about 1.2 °C so far although today's forcing would eventually bring more.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.