Climate Glossary  (press Ctrl-F to search for a word, or -F on a Mac)

(Also available in alphabetical order.)

WUWT (the top-rated science blog site on the Web, created by climatologist Anthony Watts). 
Watts, Anthony
A leading "skeptical" climatologist, owner of the WUWT blog, and originator of the project. 
RC (the leading Climate Movement activist blog, with about 1/10 the readership of WUWT). 
Global Warming (a/k/a Climate Change). (Sometimes sloppily used as a synonym for AGW or CAGW.) 
Anthropogenic Global Warming (GW caused by people). 
Catastrophic Anthropogenic Global Warming (AGW). (FUD by climate industry activists.) 
United Nations Intergovernmental Panel on Climate Change (the leading Climate Movement institution). They've produced five major "Assessment Reports" on Climate Changed, dubbed FAR through AR5. Unfortunately, they have credibility problems.
IPCC 6th Assessment Report (2021-2022). It is preceded by AR5. The AR6 WGI ("physical science basis") web site is
IPCC 5th Assessment Report (2013-2014). It was preceded by AR4, and followed by AR6. The AR5 WGI ("physical science basis") web site is
IPCC 4th Assessment Report (2007). It was preceded by the TAR & followed by AR5
IPCC Third Assessment Report (2001). It was preceded by the SAR & followed by AR4
IPCC Second Assessment Report (1995-1996) [also WG I, II, III & errata]. It was the first of the IPCC Assessment Reports in which the record shows[2] that politics overrode science. It was preceded by the FAR & followed by the TAR
IPCC First Assessment Report (1990). It was followed by the SAR in 1995-1996. 
Nongovernmental International Panel on Climate Change, producer of the “Climate Change Reconsidered” reports.
Astronomy Picture Of the Day (a/k/a APOTD). 
Notoriously-leftist Public Radio. 
NASA Goddard Institute for Space Studies, in New York City (oddly enough, handlers of U.S. surface temperature records). For several years GISS blocked the archiving of averaged USHCN temperature data, but I've compiled a collection of all known versions
NASA Jet Propulsion Lab, in Pasadena, CA. 
Permanent Service for Mean Sea Level. 
National Oceanic and Atmospheric Administration. 
NOAA National Climatic Data Center. 
NOAA Center for Operational Oceanographic Products and Services. 
NOAA Climate Monitoring and Diagnostics Laboratory, now part of the ESRL
NOAA Earth System Research Laboratory
National Snow and Ice Data Center. 
NCDC United States Historical Climatology Network - keepers of historical U.S. surface station climate records. See also and USCRN
NCDC's U.S. Climate Reference Network seeks to solve the data quality problems of the USHCN. It is composed entirely of high-quality, well-sited measurement instruments. Unfortunately, the records are short. The first USCRN stations were installed in 2002.
A volunteer project led by climatologist Anthony Watts to analyze, station-by-station, the entire USHCN station network. See also UHI
Stevenson screen
A "Stevenson screen" or "Cotton Region Shelter" is a louvered instrument enclosure for meteorological instruments, such as thermometers. 
Six's registering thermometer
A type of min-max thermometer, invented by James Six in 1780, and very widely used for over 200 years (often within Stevenson screens) to measure daily minimum and maximum temperatures. 
Automated Surface Observing System
Land Surface Temperature. 
Urban Heat Island effect (UHI) is the phenomenon of cities having higher average temperatures than the surrounding countryside. It can distort measured surface temperature trends, because as cities grow they can cause rural temperature gauge locations to become urban locations, resulting in a spurious apparent warming trend. See and homogenization
“Climate Sensitivity” is a measure of the (in)stability of the Earth's temperatures, most commonly defined as the globally averaged temperature increase to be expected from a doubling of atmospheric carbon dioxide (e.g., an increase from 300 ppmv to 600 ppmv). (See also TCR, ECS & ESS.)
The most straightforward way of estimating climate sensitivity is by examining the result of the “experiment” which mankind has performed on the Earth's climate (by raising atmospheric CO2 levels from near 300 ppmv to above 400 ppmv), noting what happened to temperatures, and extrapolating from those observations.
Climate sensitivity estimates in the scientific literature vary wildly, but have generally been declining, as discussed on the Resources page (though many CMIP6 models buck that trend). 
Transient Climate Response, a measure of climate sensitivity over a relatively short time frame (e.g., 20 years).
It is formally defined to be the effect on the Earth's average global near-surface air temperature after seventy years, of increasing the atmospheric CO2 level by 1% per year (a rate of increase which would double the CO2 level in seventy years). That's about twice as fast as the CO2 level has been rising over the last forty years, so TCR is less than the “practical climate sensitivity” implied by already-realized warming. 
Either “Equilibrium Climate Sensitivity” (EqCS) or “Effective Climate Sensitivity” (EfCS), two similar measures of long-term climate sensitivity. “Long-term” means a few hundred years, so ECS is greater than the “practical climate sensitivity” implied by already-realized warming.
I've seen the ECS-to-TCR ratio variously estimated between 1.25:1 and CSIRO's 2.28:1, with 1.5:1 being typical.
AR5 estimates ECS to be between 1.5 & 4.5 °C (central value 3.0°C). Other scientists, like Bates (2016), estimate ECS to be 1.0 °C or less. I think the IPCC's estimate is too high. Over the 21st century, the trend has been toward lower estimates of climate sensitivity (though many CMIP6 models buck that trend). 
Earth System Sensitivity, the estimated extremely long-term climate sensitivity to a doubling of CO2, after the effects of ice sheet changes are fully felt, and deep-ocean temperatures stabilize (i.e., after tens of thousands of years).
It is a theoretical concept, not very relevant to the climate debate, since it hypothesizes an elevated plateau in atmospheric CO2 levels which is far longer than the anthropogenic CO2 spike could persist. 
Ocean Heat Content. 
Hansen, James
A controversial elder leader of the Climate Movement, retired April 3, 2013 as director of the NYC office of NASA GISS. In 1988, 3½ months before the U.N. created the IPCC, Hansen was lead author of a highly influential paper predicting catastrophic global warming. He and his colleague, Makiko Sato, have a web page about sea-level here
Atlantic Multi-decadal Oscillation: a very long-duration oscillatory pattern to North Atlantic weather, with an estimated period of about 60-70 years. (See also PDO, ENSO & MJO.) 
Pacific Decadal Oscillation: a long-duration oscillatory pattern to Pacific weather, especially in the Northern Pacific, with a period of about 15-30 years. (See also AMO, ENSO & MJO.) 
El Niño / La Niña - Southern Oscillation, a well-known, semi-oscillatory pattern to Southern and equatorial Pacific ocean temperatures, with a period of about 3-5 years, and global weather effects. (See also AMO, PDO & MJO.) 
Indian Ocean Dipole: a semi-oscillatory ENSO-like climate cycle in the Indian Ocean, which affects weather patterns in Africa and Australia. (See also AMO, PDO & ENSO.) 
Madden-Julian Oscillation is a little-known, short-duration oscillatory pattern to tropical & subtropical weather (roughly ±30° latitude), which can occur several times per season. (See also AMO, PDO & ENSO.) 
The Quasi-Biennial Oscillation is a remarkably regular 28-month cycle governing wind direction in the stratosphere, above the tropics. 
Time of OBServation, variations of which can bias temperature measurements, which is the rationale for some of the striking “homogenization” adjustments to old temperature records, which have made the past reportedly colder and the present warmer, bolstering the apparent case for GW
Adjustments of scientific data, most commonly temperature data, to hopefully correct errors and biases (“inhomogeneities”), such as those caused by station moves, instrument changes, TOBS, UHI, etc. The details of those adjustments can have a dramatic effect on reported temperature trends. 
A “computer model” (or just “model”) is a computer program which simulates (“models”) real processes for the purpose of predicting their progression. (Other sorts of models also exist, such as mathematical models, and physical scale models; all of them are attempts to approximately simulate, and thereby predict, reality.)
The utility and skillfulness of models is dependent on how well the processes which they model are understood, how faithfully those processes are simulated in the computer code, and whether the results can be repeatedly tested so that the models can be refined.
Specialized models, which try to model reasonably well-understood processes, like PGR and radiation transport, are useful, because the processes they model are manageably simple and well-understood. Weather forecasting models are also useful, even though the processes they model are very complex, because the models' short-term predictions can be repeatedly tested, allowing the models to be validated and refined.
But more ambitious models, like GCMs, which attempt to simulate the combined effects of many poorly-understood processes, over time periods too long to allow repeated testing and refinement, are of dubious utility. (Worst of all are so-called “semi-empirical models,” which aren't actually models at all.) 
General Circulation Model, a large, complex computer program which attempts to simulate (“model”) the Earth's climate. Also called “Atmosphere-Ocean General Circulation Model” (AOGCM). Most of the latest GCMs are participants in the “Coupled Model Intercomparison Project, Phase 6” (CMIP6). 
So-called “semi-empirical modeling” is an oxymoron: “modeling” that doesn't actually model anything. It is similar to modeling, but without reference to any physical basis. It is really just curve-matching. It can be made to produce just about any desired result.
GCMs are subject to criticisms that they don't accurately model the real world, because of inconsistency with observations of things like clouds and the predicted tropical mid-tropospheric hot spot. Semi-empirical modelers neatly avoid such criticism, by not even trying to model the real world. It's the worst sort of junk science. 
A well-known radiation transport model, which models atmospheric radiation propagation for wavelengths between 0.2 µm and 100 µm. 
Mean Sea-Level. 
Local Mean Sea-Level (MSL measured at a specific place), also called RSL (Relative Sea-Level). 
Global Mean Sea-Level (any of many varieties of average MSL). 
Sea-Level Rise. 
Eustatic SLR
Global Sea-Level Rise = GMSL Rise. 
“Due to changes in loading of the crust of the earth” (especially due to melting ice sheets circa 10,000 years ago). See also GIA
Sinking of the land. It is often caused by extraction of groundwater, oil and/or natural gas, or due to PGR. River deltas (notably including the Mississippi River Delta) typically subside because of loading from past sediment deposition, which may have been reduced due to flood control. In many places, subsidence has a greater effect on local (“relative”) sea-level trends than does global sea-level rise. 
Wild-Ass Guess; also “SWAG” = Scientific Wild-Ass Guess; see also "proxy." 
Fear, Uncertainty & Doubt. The acronym originated to describe a marketing ploy used in the IT industry in the 1970s, but it is now the foundation of climate activism. (See also “carbon pollution.”) 
Carbon pollution
What climate activists call producing carbon dioxide (by combustion, cement manufacturing, exhaling, etc.), and methane. (See also FUD.) 
Climate crisis
The “climate crisis” or “climate emergency” is terminology used by climate activists to promote FUD about AGW
Post-Glacial Rebound, isostatic movement of the earth's crust due to the last major deglaciation (circa 10,000 years ago); it causes falling sea-levels in Scandinavia, around Hudson Bay, and elsewhere
Glacial Isostatic Adjustment, a (rough!) calculated adjustment to SLR to account for vertical land motion from PGR
Peltier, Wm Richard
The University of Toronto professor who calculates estimates of GIA from computer models
Peltier's most commonly-used model-derived GIA data set; also, the "earth model" used for it. 
Peltier's alternative model-derived GIA data set; also, the "earth model" used for it. 
The “ice model” used by Peltier to calculate his GIA data sets. 
Tide station
A device for measuring coastal sea-level; also called a tide gauge
Global Sea-Level Observing System (a set of hundreds of tide-stations, some of which have been operating for over 200 years). 
U.S. National Water Level Observation Network
Australia's Great Barrier Reef. 
Daly, John L.
John Daly was a leading Australian climate skeptic, who created the Still Waiting For Greenhouse climate website, and died January 29, 2004. 
Hameranta, Timo
Timo Hämeranta, LL.M. was a leading Finnish climate skeptic, who founded and moderated the ClimateSceptics scientific discussion group in 2001. He died in late 2009. 
Jones, Phil
Dr. Phil Jones is an English leader of the Climate Movement, who infamously called the untimely death of John Daly "cheering news." 
The “Climategate” scandal was the result of a pair of “document dumps” in 2009 and 2011, by a still-anonymous whistle-blower calling himself “FOIA.” They include climate-related emails, documents & computer code, which show that leading Climate Movement scientists had been manipulating & withholding data, hiding evidence, flouting FoIA laws, and blackballing skeptics, to promote CAGW.
Phil Jones' email to Michael Mann about the "cheering news" of John Daly's death was one of those released. (See also Fakegate.) 
A scandal, in which the Climate Movement's top ethicist, Dr. Peter Gleick (assisted by DeSmogBlog), was caught committing identity theft, defamation & forgery, to smear Heartland Institute.  (See also Climategate.) 
University of East Anglia's Climate Research Unit, source of the Climategate files. 
The Current Warm Period, Present Warm Period (PWP), Modern Climate Optimum, or simply Modern Optimum (MO), circa 1900 A.D. to present. Preceded by the LIA. Similar to the MWP, RWP & BAWP
Little Ice Age, circa 1350-1850 A.D., when temperatures were much colder than they are now. Preceded by the MWP, and followed by the CWP
Medieval Warm Period (a/k/a Medieval Climate Optimum, Little Climate Optimum, or Medieval Climate Anomaly), circa 850 to 1300 A.D., when temperatures were probably about as warm as they are now. Preceded by the DACP, and followed by the LIA. (See also RWP, BAWP & HCO.) 
Dark Ages Cold Period (a/k/a European Migration Period or Late Antiquity Little Ice Age [LALIA]), circa 400 to 800 A.D. (or 500 to 700 A.D.), when temperatures were significantly colder than they are now. Some revisionist authors disdain the term “DACP” and prefer “LALIA” because they think “dark” is “pejorative.” The DACP was preceded by the RWP, and followed by the MWP
Roman Warm Period, circa 250 B.C. to 350 A.D., when temperatures were probably at least as warm as they are now. Preceded by the Iron Age Cold Period, and followed by the DACP. (See also MWP, BAWP & HCO.) 
The “Iron Age Cold Period,” (a/k/a Iron Age Cold Epoch, or Iron Age Neoglacial), circa 1200 B.C. to 300 B.C., was an extended cold period, preceded by the BAWP and followed by the RWP. See also LIA & DACP.) 
Minoan Warm Period
The Bronze Age Warm Period (BAWP) or Minoan Warm Period, roughly circa 1450 B.C. to 1200 B.C., was a period when temperatures were apparently at least as warm as they are now. It was followed by the long IACP. (See also HCO, RWP & MWP.) 
Holocene Climate Optimum
The Mid-Holocene Warm Period, Mid-Holocene Climatic Optimum, Altithermal, Hypsithermal, Thermal Maximum, or Holocene Climate Optimum (HCO), was an extended period from about 7,000 B.C. to about 3,000 B.C., or perhaps somewhat later, when temperatures were apparently warmer than present, at least most of the time. Some researchers subdivide it into several shorter warm periods, separated by relatively cooler periods. (See also BAWP, RWP & MWP.) 
The Holocene Interglacial is the current interglacial (warm) period, which began circa 9700 B.C., and has lasted almost 12,000 years, so far.  It was preceded by the last glacial period. The previous interglacial was the Eemian
Last glacial period
The last glacial period was the most recent period when ice sheets covered most of northern North America and northern Europe, and sea-levels were much lower than present. It is considered to have begun circa 113,000 B.C., and ended circa 9700 B.C., with maximum ice sheet extent (“LGM”) circa 25,000 to 17,000 B.C.  It was preceded by the Eemian interglacial, and followed by the Holocene
Younger Dryas
Near the end of the last glacial period, immediately following the Bølling-Allerød interstadial, the global warming trend temporarily reversed (at least in the northern hemisphere) during the frigid Younger Dryas (YD), which began about 10,800 B.C., and lasted for about 1300 years. The end of the YD is generally considered to mark the start of the Holocene
Dansgaard-Oeschger events
Dansgaard-Oeschger events (“D-O events”), a/k/a Greenland Interstadials, were sudden warming events which punctuated the last glacial period, during which northern hemisphere temperatures rose at rates as rapid as several degrees per decade. (Southern hemisphere temperature changes were apparently much more gradual.) Greenland ice cores record two dozen D-O events, the last of which was the Bølling-Allerød Interstadial, which was followed by the final cold period of the last glaciation, the frigid Younger Dryas
Last Glacial Maximum, circa 25,000-17,000 B.C., when the northern hemisphere ice sheets were at their maximum extent, during the last glacial period
The Eemian Interglacial, a/k/a the Last Interglacial (LIG) or Eemian Optimum, was the interglacial (warm) period before the last glacial period. It lasted about 15,000 years. Reconstructions suggest that, at its peak, the Eeemian was several degrees warmer than the warmest part of the Holocene. It began circa 128,000 B.C., ended roughly 113,000 B.C., and was followed by the last glacial period, and then by the current Holocene
“BP” is, literally, an abbreviation for “before present,” but that's usually not what it actually means. Due to an obscure and unfortunate convention of the paleoclimate community, “BP” usually means “before 1950 A.D.”  See also “ka.” 
“ka” is an abbreviation for “kilo annum,” literally meaning “thousand(s) (of) years before present.” It is slightly ambiguous, because it can mean either before the current date, or before 1950. See also “BP” and “Ma.”” 
“Ma” is an abbreviation for “mega annum,” meaning “million(s) (of) years before present.” See also “ka.”” 
Climate data from long ago, before there were good measurements. 
“Climate proxies” are indirect methods of attempting to infer paleoclimate data from other things, such as tree rings, sediment layers, and isotope ratios; see also "WAG." 
“Representative Concentration Pathways” are what the IPCC calls their four AR5 climate model scenarios: RCP2.6, RCP4.5, RCP6 & RCP8.5, with the number representing the size of the expected net radiative forcing in year 2100, in W/m2 (2.6 W/m2 to 8.5 W/m2). Those radiative forcing numbers are relative to the year 1750 (during the Little Ice Age), and they assume large net positive (amplifying) feedbacks and resultant high climate sensitivity, for which there is scant evidence. 
Total Solar Irradiance (TSI) is the average intensity of solar radiation at Earth's TOA, a/k/a the Solar Constant. Estimates of its value, from satellite measurements (1979-present), are in the range of 1360 to 1373 W/m²[1][2][3][4][5][6][7][8], with recent estimates converging on 1360 to 1362 W/m². See also solar contant, radiative forcing, ERB, ACRIM & SORCE. (The average irradiance over the entire Earth is 1/4 of TSI, because the surface area of a sphere is 4× the area of a circle of same radius, so if the solar constant is taken as 1362 ±2 W/m² then the average irradiance is 340.5 ±0.5 W/m².) 
Solar constant
“The solar constant” is a synonym of TSI: the total solar irradiance at Earth's top of atmosphere, where the Earth directly faces the Sun, when the Earth is one AU from the Sun. Just how “constant” the Solar Constant really is is disputed[1][2]. 
“Top of Atmosphere” (taken literally it would mean the exosphere, but in some contexts it may mean the mesosphere or mesopause). 
Lapse rate
The “lapse rate” is the slope of the temperature profile vs. altitude, in the atmosphere.
In the troposphere (where we live), the lapse rate is positive, meaning that air temperature generally descreases with altitude (except in special circumstances, like over the Antarctic Plateau). At the tropopause, temperatures don't change much with altitude changes. In the stratosphere, temperatures increase with altitude. Here's a graph.
The average lapse rate within the troposphere is said to be about 6.5°C/km, but the “dry adiabatic lapse rate” is 9.8°C/km, and the “moist adiabatic lapse rate” is only about 6°C/km. Here's a video about it.
Lapse rate feedback” is a “negative” (stabilizing) feedback caused by changes in the tropospheric lapse rate which occur as a result of climate change. It reduces the effect of GHGs on surface temperatures. 
Radiative forcing
Radiative forcing” (RF or ΔF) is change in average solar radiation intensity at TOA, or (more often) the equivalent effect from changes in other factors, like GHG concentrations or albedo. It is customarily expressed as an average, over the entire globe, so a 1 W/m2 increase in TSI would be a 0.25 W/m2 RF. Related acronyms include IRF (Instantaneous Radiative Forcing) and ERF (Effective Radiative Forcing). 
NASA's Earth Radiation Budget satellite mission measured TSI (among other things). 
Active Cavity Radiometer Irradiance Monitor [2] was a NASA satellite instrument which measured Total Solar Irradiance (TSI). 
NASA SOlar Radiation & Climate Experiment satellite mission. It measures TSI (among other things). 
NASA International Satellite Cloud Climatology Project
European SOHO Variability of solar IRradiance and Gravity Oscillations satellite mission. It measures TSI (among other things). 
NASA's CERES (Clouds and the Earth's Radiant Energy System) satellite missions measure radiation emitted from and reflected by the Earth using narrow-field, downward-looking radiometers. (Not to be confused with a French surveilance satellite with the same acronym.) 
The Gravity Recovery and Climate Experiment was a NASA satellite mission which measured variations in the Earth's gravitational field, from March 2002 until October 2017. GRACE-FO (“GRACE Follow On”) is the follow-up mission, which launched May 22, 2018. 
The Ice, Cloud,and land Elevation Satellite was a NASA satellite mission, which measured surface topography via laser altimetry (Lidar). It launched in 2003, but failed prematurely, due to a design defect. It provided limited data until 2009. ICESat-2 is the follow-up mission, which launched September 15, 2018. 
CryoSat-2 is a European Space Agency satellite mission which measures polar ice caps with radar altimetry. It launched April 8, 2010. (The predecessor CryoSat-1 satellite was lost in a launch failure.) 
Mann, Michael
A leading U.S. Climate Movement scientist, who, with coauthors Raymond Bradley & Malcolm Hughes, famously created a (since discredited) "hockey-stick" shaped graph of paleo-temperature data from tree-ring proxies, which appeared to erase the MWP & LIA from history. 
Muller, Richard
A leading U.S. Climate Movement scientist, who was critical of Michael Mann after the Climategate revelations. 
Steve McIntyre and Ross McKitrick, Canadian researchers who famously discredited Michael Mann's “hockey stick” with their 2003 paper
What climate activists call those who disagree with them (a scornful reference to Holocaust deniers). 
Intersectional science
A leftist project to “bring science and social justice together,” incorporating the struggle against racial and gender oppression into the study and practice of science. 
Sea Surface Temperature. 
Thermohaline Circulation or Meridional Overturning Circulation (MOC) refers to the “Atlantic Conveyor” (AMOC) and related currents which carry warm surface water from the tropics toward the poles (most famously via the Gulf Stream), and currents deep in the ocean which carry cold water back toward the tropics. 
Aircraft Meteorological Data Relay (see NOAA's FAQ). 
Infrared light. 
Shortwave Radiation (esp. incoming radiation from the Sun, which is mostly near-infrared, visible, and shorter wavelengths). 
Outgoing Longwave Radiation (the far-infrared and microwave energy radiated by the Earth). 
A number between 0 and 14 (with 7 being neutral), which specifies how acidic or basic/alkaline/caustic an aqueous solution is; technically, the negative base 10 logarithm of the hydronium ion concentration. The pH of seawater varies between 7.2 and 8.4 (i.e., slightly caustic). 
Cloud Radiative Effect (CRE) refers to the varying effects of clouds on incoming/downwelling and outgoing/upwelling radiation to/from the earth's surface. At night clouds have a warming effect, but in daytime clouds shade & cool the surface. The net effect is complex and poorly understood. 
Greenhouse Gas: any trace gas (such as CO2, CH4 or water vapor) which helps warm the Earth's surface by blocking far IR emissions into space. (Note: the term “greenhouse gas” is a misnomer, because that's not the main way that greenhouses actually work.)
To be a greenhouse gas, a gas must be radiatively active in the “far” (longwave) infrared, at wavelength(s) longer than about 4 µm, so that it can absorb more outgoing radiation (from the Earth) than incoming radiation (from the Sun). 
“Long-Lived Greenhouse Gases” (a/k/a “non-condensing greenhouse gases”), i.e., GHGs other than water vapor. 
CO2 or CO2
Carbon dioxide, the most important non-condensing greenhouse gas, the “precious air fertilizer” (SciAm), a colorless, odorless trace gas, formerly called “carbonic acid gas,” the raw material for plant growth, the bubbles in soda pop, the stuff you exhale. 
CH4 or CH4
Methane, a greenhouse gas, the main component of natural gas and flatulence. When burned, it oxidizes into CO2 and water. If released into the atmosphere, it oxidizes more slowly, with a half-life of about six to eight years
“CO2e” or “CO2 equivalent” (not to be confused with eCO2) is an attempt to roughly approximate the combined warming effect of all anthropogenic GHGs, by adding to CO2 concentration a weighted sum of the concentrations of other anthropogenic GHGs. Here's an example of one such weighting formula. 
“eCO2” is an abbreviation for “elevated CO2” (not to be confused with CO2e). 
pCO2 or pCO2
Partial pressure of CO2.
In the Earth's atmosphere, as of 2023, the dry partial pressure of CO2 averages about 420 ppmv (parts per million by volume = micromoles per mole = µmol/mol).
When expressed in ppmv, pCO2 is independent of atmospheric pressure. But, especially in water, instead of being specified in ppmv, pCO2 may be given in units of µatm, which depend on pressure. At 1 atm the units are equal.
The equilibrated ratio of atmospheric CO2 partial pressure to dissolved CO2 concentration in water is governed by solubility, which varies with temperature and salinity. The solubility of gases like CO2 (or CH4) in water decreases as the water warms, according to the temperature dependence of Henry's law. The capacity of the water to hold dissolved CO2 decreases by about 3% per 1°C that the water warms. For details see this technical note from Pro-Oceanus Systems Inc. 
Abbreviation for “gigatonne” (one billion metric tonnes = 1012 kg). A synonym for “petagram.” 
Abbreviation for “petagram” (1015 grams = 1012 kg). A synonym for “gigatonne.” 
Abbreviation for “petagrams of carbon” = gigatonnes of carbon. 1 ppmv CO2 = 7.8024 Gt CO2 = 2.12940 PgC. 
“CDR” can be an abbreviation for either of two unrelated things: 1. NOAA Climate Data Record (note: this is what the plural “CDRs” means);  Or, 2. “Carbon Dioxide Removal” (which refers to manmade schemes to remove CO2 from the atmosphere, not the negative feedbacks which remove CO2 from the atmosphere naturally).

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