| Scenario | CO2 (ppm) | CH4 (ppb) | N2O (ppb) | Albedo | Solar (W/m²) | Other (W/m²) | Total Forcing (W/m²) |
|---|---|---|---|---|---|---|---|
| Baseline | 280 → 280 | 700 → 700 | 270 → 270 | 0.30 → 0.30 | 1361 → 1361 | 0.00 | 0.000000 |
| Moderate increase | 280 → 420 | 700 → 1900 | 270 → 335 | 0.30 → 0.30 | 1361 → 1361 | -0.50 | (computed by tool) |
| Albedo shift | 280 → 420 | 700 → 1900 | 270 → 335 | 0.30 → 0.29 | 1361 → 1361 | -0.20 | (computed by tool) |
- CO2 forcing: ΔFCO2 = k · ln(C/C0)
- CH4 forcing (simplified): ΔFCH4 = k · (√M − √M0)
- N2O forcing (simplified): ΔFN2O = k · (√N − √N0)
- Solar forcing: ΔFsolar = (1 − α)/4 · (S − S0)
- Albedo forcing: ΔFalbedo = −S/4 · (α − α0)
- Total forcing (component mode): ΔFtotal = ΣΔF + ΔFother
- Temperature estimate: ΔT ≈ λ · ΔFtotal
- Enter baseline and current values for gases, albedo, and solar input.
- Keep coefficients at defaults unless you have a justified alternative.
- Add any extra forcing terms as a single “Other Forcing” value.
- Press Calculate to show results above the form.
- Use the download buttons to export your latest run.
Radiative forcing in the energy budget
Radiative forcing measures how a driver changes the net energy flow at the top of the atmosphere. It is expressed in W/m², letting you compare gases, aerosols, clouds, and surface changes on one scale. Positive forcing tends to warm, negative forcing tends to cool. The calculator separates components for clear auditing.
CO2: logarithms and diminishing increments
CO2 forcing is commonly approximated as ΔF = k ln(C/C0). The logarithm reflects partial saturation of absorption bands: each added ppm has a smaller effect than earlier ppm. With k≈5.35, moving from 280 to 420 ppm gives ln(1.5)≈0.405 and ΔF≈2.17 W/m².
CH4 and N2O: quick sensitivity terms
Methane and nitrous oxide are represented here with square-root forms, ΔF = k(√X − √X0), capturing diminishing returns at higher abundance. Detailed methods include spectral overlap corrections; this tool omits overlap to stay lightweight. For inventory-grade studies, enter a vetted forcing as “Custom Total.”
Solar forcing and global averaging
The solar constant near 1361 W/m² applies to the Sun-facing disk. Global mean changes use a 1/4 factor because Earth’s surface area is four times the disk area. The calculator applies ΔFsolar = (1 − α)/4 · (S − S0), so small S changes translate consistently to W/m².
Albedo shifts can rival greenhouse terms
Albedo summarizes reflected sunlight from clouds, ice, land cover, and aerosols. Because incoming solar energy is large, small albedo shifts matter. Using ΔFalbedo = −S/4 · (α − α0), an albedo drop of 0.01 at S=1361 gives about +3.40 W/m², a strong warming push.
Interpreting signs and “Other Forcing”
Check signs carefully. Higher albedo produces negative forcing, while lower albedo produces positive forcing. “Other Forcing” is a flexible slot for aerosols, land-use effects, volcanic impacts, or any external estimate. If you model aerosols separately, keep that term negative to reflect net cooling in most scenarios.
Linking forcing to temperature response
A first-order temperature estimate uses ΔT ≈ λ·ΔF, where λ is an effective sensitivity in K per W/m². A common illustrative choice is λ≈0.8, so +2.5 W/m² suggests about +2.0 K. This is not a full climate model; it is a consistent comparison lens.
Scenario design and reproducible reporting
Build scenarios incrementally: change one driver, record the component breakdown, then add the next driver. Export CSV for spreadsheets and PDF for reports so assumptions travel with the numbers. Share your baseline, coefficients, and sign conventions with collaborators to keep comparisons meaningful and repeatable. Prefer documenting units, sources, and dates for inputs, especially when comparing multi-year policy pathways.
Q1. What is radiative forcing measured in?
It is measured in watts per square meter (W/m²), representing the change in net energy flux after a perturbation. Using W/m² allows direct comparison of different climate drivers on the same physical scale.
Q2. Why does CO2 forcing use a logarithm?
CO2 absorption bands partially saturate as concentration rises, so each additional ppm adds less forcing. A logarithmic form captures this diminishing incremental effect while remaining accurate for broad concentration ranges.
Q3. Are CH4 and N2O values exact here?
No. The CH4 and N2O terms are simplified square‑root approximations and do not include spectral overlap corrections. For stricter analysis, compute forcing externally and enter the result as a custom total.
Q4. How do I represent aerosols or volcanic cooling?
Use “Other Forcing” as a single value. Enter negative numbers for net cooling and positive numbers for net warming. Keep your sign convention consistent across scenarios and document the source of each estimate.
Q5. What does the albedo term represent?
It represents changes in reflected sunlight from clouds, ice, land cover, and particles. Lower albedo generally increases absorbed solar energy and gives positive forcing, while higher albedo reflects more sunlight and gives negative forcing.
Q6. What does the temperature estimate mean?
It is a first‑order estimate using ΔT ≈ λ·ΔF, where λ is an effective sensitivity. It helps compare scenarios under consistent assumptions, but it does not replace a full climate model with feedbacks and ocean dynamics.
Q7. Can I export results for reporting?
Yes. After a calculation, use the CSV download for spreadsheets and the PDF download for a compact report. Exports reflect your latest run, so recalculate after any input changes.