The Energy Budget Model
Earth radiates almost exactly what it absorbs — almost — and the gap is what a century of thermometers has been measuring.
Phase 0 · The phenomenon
A budget that does not quite balance
A bar chart: incoming sunlight 340, reflected 100, absorbed 240 and outgoing infrared 239 watts per square metre. A small extra bar labelled "the gap, about 1" is drawn enlarged beside them.
Every second, sunlight delivers about 340 watts to each square metre of Earth, averaged over the whole globe, day and night. About 100 of those watts bounce straight back to space off clouds, ice and bright ground. The planet absorbs the other 240.
Earth sends energy back out as invisible infrared light — and satellites measure that it sends back almost exactly 240 watts per square metre. Almost. Around 2019 the shortfall was about 1 watt per square metre, double what it was in the mid-2000s.
One watt out of 240 sounds like nothing. In this lab you will build Earth's energy budget from scratch and find out what that one watt adds up to.
Why does Earth sit at the temperature it does — and what happens when it absorbs even slightly more energy than it radiates?
What this lab works toward
HS-ESS2-4Use a model to explain how changes in the energy flowing into and out of Earth's systems change climate.HS-ESS3-5Analyze data and climate-model results to forecast the rate of climate change and its impacts.
Plain-English summaries. The course maps these performance expectations to this lab; the official wording is published at nextgenscience.org.
The stations
- Bare Rock PlanetWhat temperature balances sunlight in and infrared out on a planet with no atmosphere?
- Greenhouse LayerHow does a layer that absorbs infrared make the surface warmer?
- The GapHow much heat does a 1 W/m² imbalance pile up, and where does it go?
- CO₂ ForcingHow much warmer does Earth get as carbon dioxide rises?
Each station runs the same loop: predict before you see any data, investigate the model and record runs, reveal what the measurements show, then explain the gap between your prediction and the result. A claim-evidence-reasoning checkpoint and an exit ticket close the lab.
- Earth is treated as one point with one average temperature. Real temperatures vary hugely with latitude, season and time of day, and energy is moved around by winds and currents.
- The atmosphere is a single layer that absorbs a fixed fraction of the surface's infrared. Real greenhouse gases absorb in particular wavelength bands, and convection carries heat upward too.
- The ocean-warming estimate puts 90% of the imbalance into the top 700 m of ocean. Some heat actually goes deeper, so this overstates the upper-ocean rate and understates the deep ocean's.
- Warming from carbon dioxide is shown at equilibrium — after the oceans have caught up, which takes centuries. Warming observed so far is smaller than the equilibrium value for today's CO₂.
- Station 4 counts carbon dioxide only. Methane and other gases add more forcing and air-pollution aerosols take some away, so it is not a complete forecast of observed warming.