A planet wrapped in a thin atmosphere, swallowing sunlight and radiating it back. The accounting is well understood; the consequences are accelerating.
The Sun delivers ~340 W/m² to the top of Earth's atmosphere, on average. About 30 % is reflected (clouds, ice, deserts) — the planetary albedo. The remainder, ~240 W/m², is absorbed and re-radiated as longwave infrared.
Greenhouse gases — H₂O, CO₂, CH₄, N₂O, O₃ — absorb a fraction of that outgoing radiation and re-emit it in all directions, including downward. Net effect: surface stays ~33 K warmer than it would otherwise.
S0(1 − α) / 4 = σ T4eff
Stefan–Boltzmann balance with no atmosphere: Teff = 254 K = −19 °C. With greenhouse: 288 K = 15 °C.
Air bubbles in Antarctic ice (Vostok, EPICA, Dome C cores) preserve a direct sample of past atmospheres. CO₂ in the Pleistocene oscillated between 180 ppm (glacials) and 280 ppm (interglacials), driven by orbital pacing and amplified by ocean–carbon and ice-albedo feedbacks.
The Milankovitch cycles — eccentricity (100 kyr), obliquity (41 kyr), precession (23 kyr) — set the rhythm. The amplitude is the climate system responding.
We blew through the natural ceiling around 1950. CO₂ has not been this high in at least 3 million years (mid-Pliocene), when sea level was 15–25 m higher than today.
Three independent fingerprints converge on anthropogenic CO₂ as the main driver:
IPCC AR6 (2021): "It is unequivocal that human influence has warmed the atmosphere, ocean and land."
IPCC AR6 effective radiative forcings, 1750–2019.
The ocean has absorbed ~91 % of the excess heat trapped by greenhouse gases since 1970, and ~26 % of anthropogenic CO₂. It is the planet's thermal flywheel.
Consequences: thermal expansion (~⅓ of observed sea-level rise), acidification (pH down ~0.1 unit), oxygen loss in many regions, slowing of the Atlantic Meridional Overturning Circulation, marine heatwaves of unprecedented intensity (e.g. North Atlantic 2023, Mediterranean 2022).
Mass loss ~270 Gt/yr, 2002–23 (GRACE/GRACE-FO). 7.4 m of potential SLR locked up.
~150 Gt/yr loss; West Antarctic Ice Sheet contains 4.3 m SLR; Thwaites & Pine Island glaciers vulnerable.
September minimum: −13 % per decade. First ice-free summer plausible 2030s–40s.
~270 Gt/yr; ~half of Hindu Kush Himalaya glaciers gone by 2100 in current path.
~1,500 GtC stored. Thawing → CO₂ & CH₄ feedback. Yedoma especially carbon-rich.
Northern-hemisphere June extent down ~20 % since 1970. Cascading water-supply effects.
Glacial calving front. The cyanotype's natural subject — water in three states.
Single-layer energy balance. T = ((1−α) S₀ / 4σε)^(1/4). On a postcard.
Latitudinal or vertical column models. Manabe–Wetherald (1967): radiative-convective with H₂O feedback.
3-D atmosphere/ocean general circulation models. ~25-100 km horizontal grid; primitive equations.
Earth System Models: GCM + carbon cycle, dynamic vegetation, ice sheets, atmospheric chemistry.
CMIP6 (2019–) coordinates ~50 modeling groups. Hindcasts since 1850 reproduce the warming pattern only when anthropogenic forcing is included. Forecasts range from SSP1-1.9 (best case, ~1.5 °C peak) to SSP5-8.5 (~4.5 °C by 2100).
1768–1830. First to argue, 1824, that Earth's atmosphere acts as an insulator.
1856. Showed CO₂ absorbs heat — predating Tyndall by 3 years.
1859. Quantified IR absorption of H₂O, CO₂, CH₄.
1896. First quantitative climate sensitivity calc — ~5 °C per doubling.
1957. "Geophysical experiment"; ocean uptake limits on CO₂.
1958–. The Mauna Loa CO₂ curve.
1967, 2021 Nobel. First reliable CO₂-doubling GCM.
1988 testimony to U.S. Senate; raised public alarm.
Fourier proposes the greenhouse mechanism.
Foote: "An atmosphere of [CO₂] would give to our earth a high temperature."
Arrhenius computes ΔT for ×2 CO₂.
Guy Callendar links CO₂ rise to observed warming.
Keeling begins continuous CO₂ measurement at Mauna Loa.
Charney Report: ECS = 1.5–4.5 °C.
IPCC founded; Hansen testifies.
UN Framework Convention on Climate Change (Rio).
Kyoto Protocol signed / enters force.
Paris Agreement: hold < 2 °C, pursue 1.5 °C.
IPCC AR6 WG1: human role unequivocal.
First calendar year > 1.5 °C above preindustrial.
"It is unequivocal that human influence has warmed the atmosphere, ocean and land."— IPCC AR6 WG1, Summary for Policymakers, 2021
Frequency & intensity rise faster than the mean. Pacific NW 2021: +5σ event, attributed virtually impossible without warming.
Frequency uncertain; intensity (Cat 4–5) and rainfall up. Slower translation = more flooding.
Wet regions wetter, dry drier; extremes amplified. Western US "megadrought" 2000–22 worst in 1,200 yr.
VPD ↑, fire season ↑. 2023 Canadian fires emitted ~1,300 Tg CO₂ — > many countries.
Crop yield projections −5 to −30 % by mid-century in tropics; adaptation partial.
~37 % heat-related deaths attributable to climate change (Lancet Countdown 2024).
Cost down 90 % since 2010. ~3 TW installed globally. Adds ~600 GW/yr.
Onshore + offshore. ~1 TW installed. LCOE competitive with gas.
~10 % of global electricity. SMRs in development. Lifetime extensions.
Li-ion, sodium-ion, flow batteries, pumped hydro. Cost trajectory matches PV.
Heat pumps, EVs. Doubles end-use efficiency typically.
Direct air capture, BECCS, biochar, ocean alkalinization. Needed at GtC scale by 2050.
Reforestation, soil carbon, regenerative agriculture, halt deforestation.
Leak detection (MethaneSAT 2024), agricultural feed additives, livestock improvements.
Plus PBS Terra "Weathered" for extreme-weather attribution stories.