Anthropogenic Global Warming: Evidence and Mechanisms of Human-Induced Climate Change

Daniel Brouse and Sidd Mukherjee
February 14, 2026

Human-induced climate change, also called anthropogenic global warming, is a physical phenomenon rooted in the radiative properties of greenhouse gases (GHGs), especially CO₂, CH₄, and N₂O, and their interaction with Earth’s energy balance.

1. The Greenhouse Effect

Earth receives energy from the Sun primarily in the form of shortwave radiation (visible light and near-infrared). The planet absorbs this energy and re-emits it as longwave infrared radiation. Greenhouse gases in the atmosphere absorb some of this infrared radiation and re-emit it, warming the lower atmosphere and surface. This is the greenhouse effect, and it is governed by fundamental physics:

Net Radiation=4S(1−α)​−σT4

Where:

• $S$ = solar constant (~1361 W/m²)

• $\alpha$ = Earth’s albedo (~0.3)

• $\sigma$ = Stefan-Boltzmann constant (~5.67×10⁻⁸ W/m²K⁴)

• $T$ = Earth’s effective radiating temperature

Without GHGs, Earth’s surface would average ~255 K (-18°C). With current GHG levels, it averages ~288 K (~15°C).

2. Human Contribution via CO₂

Humans have increased atmospheric CO₂ from ~280 ppm (pre-industrial) to ~420 ppm today. This increase is not from natural sources but primarily from burning fossil fuels (coal, oil, gas) and land-use changes. The isotopic signature of carbon identifies the source:

• ¹²C, ¹³C, ¹⁴C isotopes are key:

  • Fossil fuels are depleted in ¹³C because plants preferentially absorb ¹²C during photosynthesis.

  • Fossil fuels contain no ¹⁴C (radiocarbon), as it decays over millions of years.

• The observed decline in ¹³C/¹²C ratio and ¹⁴C content confirms that the excess CO₂ comes from fossil carbon, not volcanoes or oceans.

3. Radiative Forcing

Radiative forcing ($\Delta F$) quantifies how much a GHG changes the balance between incoming and outgoing radiation:

ΔF=5.35ln(C0​C​)[W/m² for CO₂]

Explanation:

• $\Delta F$ = radiative forcing (in watts per square meter, W/m²)

• $C$ = current atmospheric CO₂ concentration (ppm)

• C0C_0C0​ = reference (pre-industrial) CO₂ concentration (ppm)

• $\ln$ = natural logarithm

Where:

• $C$ = current CO₂ concentration (ppm)

• C0C_0C0​ = pre-industrial CO₂ concentration (~280 ppm)

• The constant 5.35 comes from line-by-line radiative transfer calculations

This formula captures the logarithmic relationship: each doubling of CO₂ produces roughly the same increase in radiative forcing (~3.7 W/m² per doubling).

Other gases:

• CH₄ (methane): short-lived but ~25× more potent than CO₂ over 100 years.

• N₂O (nitrous oxide): ~298× more potent than CO₂ over 100 years.

The total forcing is the sum of all anthropogenic contributions:

ΔFtotal​=ΔFCO₂​+ΔFCH₄​+ΔFN₂O​+…

Explanation:

• ΔFtotal = total radiative forcing from all greenhouse gases

• ΔFCO₂ = forcing due to carbon dioxide

• ΔFCH₄ = forcing due to methane

• ΔFN₂O = forcing due to nitrous oxide

• “…” indicates contributions from other greenhouse gases (e.g., CFCs, HFCs)

4. Feedbacks Amplifying Warming

Initial radiative forcing is amplified by feedbacks:

• Water vapor feedback: warmer air holds more water → more greenhouse effect

• Ice-albedo feedback: melting ice lowers reflectivity → more absorption

• Permafrost carbon release: thawing peat releases CO₂ and CH₄ → additional forcing

This creates nonlinear acceleration: warming triggers processes that produce more warming — a key insight in the “Domino Effect” hypothesis.

5. Observational Evidence

1. Rising global temperatures (surface and ocean heat content)

2. Melting glaciers and ice sheets (Greenland, Antarctica, Arctic sea ice)

3. Rising sea levels

4. Atmospheric CO₂ increase with fossil fuel isotopic signature

5. Measured radiative forcing matches predictions from CO₂ and other GHGs

Summary

• Fossil fuel combustion increases CO₂ → higher radiative forcing → warming.

• The isotopic composition confirms the carbon source is anthropogenic.

• Feedback loops accelerate the warming beyond the direct effect of CO₂ alone.

• Observations match the physics and models, validating the scientific understanding of human-caused climate change.

Tipping points and feedback loops drive the acceleration of climate change. When one tipping point is toppled and triggers others, the cascading collapse is known as the Domino Effect.