# Vocabulary Back to [[Topics/Climate Change Science and Policy Debate/Climate Change Science and Policy Debate|Climate Change Science and Policy Debate]] | Term | Meaning | |---|---| | **RCP (Representative Concentration Pathway)** | Four greenhouse-gas concentration trajectories (2.6, 4.5, 6.0, 8.5 W/m² forcing by 2100) used in CMIP5 / AR5. | | **RCP8.5** | The highest RCP, built by IIASA (Riahi 2011), with ~8.5 W/m² forcing in 2100. Often mislabelled as "business as usual". | | **SSP (Shared Socioeconomic Pathway)** | Five socioeconomic narratives (SSP1–5) combined with forcing levels, e.g. SSP5-8.5, SSP2-4.5. Used in CMIP6 / AR6. | | **SSP5-8.5** | The fossil-fuelled-development pathway reaching 8.5 W/m². AR6 very-likely warming: 4.4°C (3.3–5.7°C) by 2081–2100. | | **CMIP** | Coupled Model Intercomparison Project. CMIP7 is the current phase, feeding AR7. | | **ScenarioMIP** | The CMIP sub-project that defines future scenarios. In CMIP7 it replaced SSP5-8.5 with a lower "High" scenario. | | **AR6 / AR7** | IPCC's Sixth (2021–23) and Seventh (in preparation) Assessment Reports. | | **ECS (equilibrium climate sensitivity)** | Long-run warming from doubling CO₂, once fast feedbacks act. AR6 best estimate 3°C, likely 2.5–4°C. | | **ESS (Earth-system sensitivity)** | Sensitivity including slow feedbacks (ice sheets, vegetation). Judd 2024 finds ~8°C per doubling over the Phanerozoic. | | **GMST** | Global mean surface temperature. | | **Radiative forcing** | The change in Earth's energy balance (W/m²) from a driver. For CO₂ it is ≈5.35 ln(C/C₀). | | **Logarithmic forcing** | Each *doubling* of CO₂ adds roughly the same forcing (~3.7 W/m²). It does not mean each 100 ppm halves. | | **Feedback vs. forcing** | A forcing is an external push (CO₂, the Sun); a feedback responds to warming (water vapour, ice albedo). CO₂ can be both. | | **Lead–lag** | The timing between CO₂ and temperature in ice cores. Gas-age vs. ice-age dating uncertainty is key. | | **Phanerozoic** | The eon of visible animal life, ~539 Ma to present. | | **Late Cenozoic Ice Age** | The glaciated state since Antarctic ice sheets formed ~34 Ma. | | **Quaternary** | The period since 2.58 Ma, with repeated glacial–interglacial cycles. | | **Interglacial** | A warm interval between glaciations. The Holocene (last ~11,700 years) is one. | | **Eemian** | The last interglacial, ~129–116 ka, when sea level was several metres above today's. | | **Milankovitch cycles** | Orbital variations (eccentricity, obliquity, precession) that pace ice ages. | | **PETM** | Paleocene–Eocene Thermal Maximum (~56 Ma): rapid carbon release and ~5°C+ warming. An analogue for fast change ⚠️. | | **CO₂ fertilisation** | Higher photosynthesis and water-use efficiency at elevated CO₂. | | **LAI (leaf area index)** | Leaf area per ground area. This is the satellite metric behind "greening". | | **Load / capacity factor** | Actual output divided by maximum possible output. Used to measure wind-farm decline. | | **Recovery factor** | The fraction of oil in place that is produced, typically ~35%. | | **EOR (enhanced oil recovery)** | Injecting CO₂, steam or chemicals to produce residual oil. | | **R/P ratio** | Reserves divided by annual production, in years left at current output. Not a forecast. | | **Lignite** | Low-grade brown coal, mined in open pits such as Hambach. | | **Net zero** | Balancing residual greenhouse-gas emissions with removals. | | **GEOCARB** | Robert Berner's long-term carbon-cycle models (GEOCARB III, 2001) estimating Phanerozoic CO₂ in 10-Myr steps as RCO₂, a multiple of pre-industrial. The source of many "CO₂ was 10–20× higher" charts; largely superseded by proxy compilations. | | **PhanDA** | Phanerozoic Data Assimilation: the Judd et al. 2024 reconstruction combining proxies with climate models. Its output gives both GMST and CO₂ by geological stage, from 485 Ma. | | **Hirnantian glaciation** | The short, intense Late Ordovician ice age (~445–443 Ma ⚠️), linked to the end-Ordovician mass extinction. Once cited as "ice at 4,000+ ppm"; newer proxies lower its CO₂. | | **GOBE** | Great Ordovician Biodiversification Event: a large rise in marine diversity through the Ordovician, coinciding with ocean cooling (Trotter 2008). | | **Faint young Sun** | The Sun brightens slowly over time (~1% per ~100 Myr ⚠️), so the same CO₂ produced less warming in deep time than it would today. | | **Big Five mass extinctions** | End-Ordovician, Late Devonian, end-Permian, end-Triassic and end-Cretaceous. Several are linked to rapid carbon release and warming from large igneous provinces. | | **LIP (large igneous province)** | A huge outpouring of volcanic rock, e.g. the Siberian Traps, that can release enough CO₂ to drive rapid warming and mass extinction. | | **CO₂ compensation point** | The CO₂ level at which a plant's photosynthesis just balances its respiration. It varies by species and temperature; C4 plants have much lower values than C3 plants ⚠️. | | **C3 / C4 photosynthesis** | The two main carbon-fixation pathways. C3 (most trees, wheat, rice) is more sensitive to low CO₂. C4 (maize, many grasses) concentrates CO₂ internally and copes better with low CO₂. | | **RCO₂** | GEOCARB's CO₂ ratio: ancient CO₂ divided by a pre-industrial baseline (~300 ppm in Berner's usage ⚠️). | | **δ13C ("delta-13-C"), ‰** | The ratio of carbon-13 to carbon-12 in a sample compared with a standard, in parts per thousand (‰, "per mil"). Plants and fossil fuels are depleted in ¹³C (about −25 to −30‰), so burning them pushes atmospheric δ13C down. It fell from about −6.6‰ in 1850 to −8.4‰ in 2015 (Graven 2020). | | **Suess effect** | The dilution of heavy carbon isotopes in air and ocean by fossil carbon: ¹⁴C (fossil carbon has none) and ¹³C. Named after Hans Suess, who found the ¹⁴C version in the 1950s. | | **Keeling plot / Keeling intercept** | A graph of δ13C against 1/CO₂ (Keeling 1958). In a simple two-part mix, the y-intercept gives the isotope signature of the added carbon. With large two-way exchange with ocean and land, the intercept no longer equals the source signature (Köhler 2006). | | **Disequilibrium flux** | The isotope effect of the gross carbon swap between air, ocean and land when their isotope ratios are out of balance. It changes atmospheric δ13C without changing the amount of CO₂, which is why δ13C moves less than fossil input alone would predict. | | **Gross vs net flux** | Gross: everything moving each way (~200 GtC/yr between air, ocean and land). Net: the difference. The amount of CO₂ follows the net flux; the isotope ratio is also shaped by the gross flux. | | **Residence time vs adjustment time** | Residence (turnover) time is how long an average CO₂ molecule stays in the air before being swapped out (~4 years). Adjustment time is how long an excess of CO₂ takes to decay (centuries, with a long tail). Mixing them up is the core error of the Harde "natural CO₂" argument (Köhler et al. 2018). | | **Bern impulse response function (Bern IRF)** | A fitted curve from the Bern carbon-cycle model giving the fraction of a CO₂ pulse still in the air after t years; roughly 20% or more stays for many centuries ⚠️. | | **Airborne fraction** | The share of human CO₂ emissions that stays in the air each year, about 45% on average; the rest goes into ocean and land sinks. | | **per meg** | The unit for tiny changes in atmospheric O₂/N₂ (1 per meg = 0.0001%). Scripps measures O₂ falling about 19 per meg per year, as expected from burning fossil fuel. | | **Bomb ¹⁴C** | The spike in atmospheric radiocarbon from 1950s–60s nuclear tests. Its decline shows how fast carbon atoms are exchanged (isotope turnover), not how fast excess CO₂ is removed. |