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  • Absorption

    Uptake of something. E.g. a photon of electromagnetic radiation is absorbed by a molecule. Earth’s atmosphere absorbs most infrared radiation from the surface.


    changing our ways of living in order to cope with the impacts of climate change. E.g. building dikes to avoid flooding from sea level rise.


    Small particles in the air. Aerosols reflect sunlight back to space and therefore lead to cooling of the surface (negative forcing). Aerosols originate from natural (dust, ash from volcanic eruptions, wave breaking) and anthropogenic (smoke) sources.


    Reflectivity. Snow, ice, clouds and other bright surfaces have a high albedo, which leads to most sunlight being reflected to space. Ocean and vegetation on land have low albedos. They absorb lots of the suns radiation, which leads to warming.


    Authorizes a utility or industrial source to emit emissions during a given compliance period. Allowances are fully marketable commodities. Once allocated, allowances may be bought or sold in a trading market.




    An anomaly is a difference or change with respect to a reference.


    Human made. Anthropogenic climate change is the change that can be attributed to human activities. Humans cause climate change by emitting greenhouse gases and aerosols, and by land use change.


    The material from which paleoclimate proxies are obtained, e.g. tree-rings, ice-cores, ocean sediment.


    The causes (natural and/or anthropogenic) of recent climate change.


    Living on or in ocean sediments.

    Biological Pump

    The removal of carbon from the surface and sequestration in the deep ocean by marine biota. Phytoplankton take up carbon during photosynthesis at the sunlit surface. They are eaten by zooplankton and the organic matter is transferred through the food web to higher trophic levels. Some of the organic matter sinks to depths, where it is remineralized by bacteria.


    a community of plants and animals occupying a major habitat


    A body that is able to absorb (and emit) electomagetic radiation at all frequencies. The Stefan-Boltzmann law states that the total energy flux from a blackbody is proportional to the fourth power of its temperature Fblackbody = σT4, where σ =5.67×10-8W/(m2K4) is the Stefan-Boltzmann constant and T is the temperature in Kelvin.

    Budget Equation

    Rate-of-Change = input – output. A budget in balance (or equilibrium) does not change: input = output.


    Assigning time to a paleoclimate record.

    Climate Sensitivity

    Sc = ΔT/ΔF is the global average surface temperature change ΔT divided by the forcing ΔF. Units are K/(W/m2). Also, commonly used is the temperature change for a doubling of CO2, ΔT2xCO2 = S*ΔF2xCO2, which can be converted easily because we know ΔF2xCO2 = 3.7 W/m2. ΔT2xCO2 is not very well known. It is most likely somewhere between 1.5 and 4.5 K. Most studies suggest it is about 3 K.


    Average seasonal cycle.


    Transition of a substance (e.g. water) from vapor to liquid. Condensation occurs when air is saturated with water vapor and condensation nuclei (e.g. small particles) are present. Latent heat is released during condensation.


    Vertical overturning of air or water due to unstable stratification. If air is heated at the surface it can lead to upward motion in the atmosphere. In the ocean convection can occur when surface waters are cooled. Deep convection in the ocean only occurs at high latitudes where surface waters are close to the freezing point.


    Flow towards a point. Convergence of surface waters in the ocean lead to downwelling. Convergence of surface winds near the equator lead to rising air in the intertropical convergence zone. See also divergence.

    Corliolis Force

    deflection of moving air or water masses towards the right (left) in the northern (southern) hemisphere due to the rotation of the Earth.


    Greek capital letter (Δ) usually used to indicate a change or difference in something. E.g. ΔT = T2 – T1 temperature change. A small delta (δ) is used for isotopes and this version (∂) indicate differentials (infinitesimally small changes). E.g. ∂T/∂t is the rate of change of temperature at any given time. It can be approximated by a difference ∂T/∂t ≅ ΔT/Δt.


    Describes a consumer's desire and willingness to pay a price for a specific good or service.


    Mass divided by volume. The density of air is approximately ρair = 1 kg/m3 (greek letter rho) and that of water is ρwater = 1,000 kg/m3. Density of air and water is lower if it is warmer. Sea water is also more (less) dense the saltier (fresher) it is.


    The question whether recent observed climate change is significant, that is outside the range expected from natural internal fluctuations only.


    flow away from one point. See also convergence.


    See models.


    Earth’s orbit around the sun is not a perfect circle but it is slightly elliptical (egg shaped). The degree of deviation from a perfect circle varies on with ~100,000 year cyclicity and is called eccentricity.

    El Niño

    El Niño years are warmer than usual temperatures in the central and eastern tropical Pacific associated with a shift of atmospheric convection from the West Pacific warm pool towards the center and eastern Pacific. La Niña years are the opposite (colder than usual temperatures in the eastern Pacific). El Niño is a phenomenon of natural, internal (unforced), variability of the coupled ocean-atmosphere system with a typical timescale of 3-7 years. It is also known as El Niño Southern Oscillation (ENSO).


    Production and discharge of something. E.g. Earth’s surface emits longwave radiation. Humans emit carbon into the atmosphere.

    Emission standard

    A standard that sets a quantitative limit on the amount of a specific air pollutant that may be released from a specific source over a given timeframe.


    Transition of a substance (e.g. water) from liquid to vapor phase. The rate of evaporation from the ocean depends on sea surface temperature (the warmer the more evaporation), the relative humidity of the air (the drier the air the more evaporation), and the wind velocity (the more wind the more evaporation). The energy required for that transition is called the latent heat of vaporization.


    The cost (or benefit) that affects a party who did not choose to incur that cost (or benefit).

    Extreme Events

    Rare weather or climate events such as hurricanes, typhoons, floods, droughts, and tornadoes that can often be damaging.

    Fallacy of False Dichotomy

    A mistake in reasoning, in which one assumes there are only two alternatives, whereas there are in fact more.


    A change in the climate system as a response to a radiative forcing that will amplify (positive feedback) or dampen (negative feedback) the initial forcing. E.g. initial forcing of increasing CO2 leads to warming, which leads to more evaporation and water vapor in the air, which leads to more warming (because water vapor is a greenhouse gas). Important feedbacks are the Planck (negative), water vapor (positive), ice-albedo (positive), lapse rate (negative) and cloud (positive or negative) feedback. The sum of all feedbacks determines the climate sensitivity.


    Amount of energy or matter flowing through an area for a certain time. E.g. the global average incident solar radiation energy flux S=342 W/m2 is the amount of energy in units of joules (J) flowing through an area of one square meter (m2) in one second (s). Watt (W) is the unit of power (1W = 1J/s). A 100 W incandescent light bulb is quite bright. Three and a-half of those per square meter is about the same energy flux as S.


    Microscopic zooplankton. Planktic foraminifera live near the surface, benthic foraminifera live on or in the sediments. Foraminifera build shells out of calcium carbonate (CaCO3) that record changes in their environment. Measurements on fossil shells are important paleoclimate proxies.


    Radiative forcing (ΔF) is a change in energy fluxes F (in W/m2) at the top-of-the-atmosphere that causes climate change. It is defined as positive (negative) if it leads to warming (cooling). The radiative forcing for a doubling of CO2 is ΔF2xCO2 = 3.7 W/m2. Other examples are increased solar radiation (positive), increased aerosols (negative) or increased surface albedo (negative), e.g. due to land use changes.


    Processes fractionate isotopes when one isotope (e.g. 16O) is preferred with respect to another isotope (18O). Evaporation, for example, favors water molecules with 16O, which causes more light water (H216O) to evaporate compared to the heavier H218O. Thus, the ratio R=18O/16O (and hence the δ18O) of water in the vapor phase will be smaller than that in the liquid phase. During condensation, the opposite happens and the heavier isotopes are preferred, which makes the cloud droplets have a higher δ18O value than the vapor they form from. Carbon isotopes fractionate during photosynthesis, such that plants (including algae) preferentially use the light 12C.


    See models.

    Great Turning

    A phrase coined by visionary Joana Macy, “the transition from a doomed economy of industrial growth to a life-sustaining society committed to the recovery of our world.”

    Greenhouse Effect

    Greenhouse gases in the atmosphere absorb part of the longwave radiation emitted from the surface of the Earth. They re-emit this radiation in all directions, half of which goes back down towards the surface, which leads to warming there. The natural greenhouse effect leads to 33 K (33°C; 60°F) warmer surface temperatures on Earth. Without greenhouse gases Earths surface would be frozen. The enhanced greenhouse effect is due to increases in greenhouse gases due to human activities and leads to global warming.

    Greenhouse Gas

    Greenhouse gases are molecules that are able to absorb and emit electromagnetic radiation in the infrared part of the spectrum (longwave). Water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are Earth’s most important greenhouse gases.

    Hadley Cell

    Atmospheric circulation in the tropics characterized by rising motion near the equator in the Intertropical Convergence Zone, poleward motion aloft (~10 km), sinking in the subtropics, and equatorward flow at the surface (trade winds).

    Heat Capacity

    The amount of heat required to increase the temperature of a substance by one degree Celsius. The specific heat capacity of air at constant pressure cp = 1 J/g°C. That of water is 4.2 J/g°C.


    The last 10,000 years of Earth’s history. A warm and stable climate. The early Holocene (10,000 – 5,000 years before the present) was about as warm as the last 30 years. After that climate cooled slowly into the Little Ice Age (1,500 – 1,800 AD).

    Human rights

    The shared standards of achievement for all people and nations, expressed in 1948 in the Universal Declaration of Human Rights, which begins with the right to life, liberty, and security of person.

    Hydrological Cycle

    The water cycle.


    Incoming solar radiation.

    Intertropical Convergence Zone

    (ITCZ) convergence of surface winds near the equator leads to rising air, cloud formation and precipitation. The ITCZ constitutes the upward branch of the Hadley Cell.

    Intrinsic Value

    As opposed to instrumental value (or use value, or value as a means to some other end) something is said to possess intrinsic value if it has value in and of itself, quite beyond or apart from the use to which it might be put.


    A group of culturally similar indigenous peoples inhabiting the Arctic regions of Greenland, Canada and Alaska


    Intergovernmental Panel on Climate Change: an international effort to synthesize the most recent science on climate change. The IPCC's assessment reports are published every 6 or 7 years and contain a comprehensive summary of the peer-reviewed scientific literature including the most recent projections.


    Flux of electromagnetic radiation (energy) through a surface per unit area. Units are watts per square meter (Wm-2).


    Versions of the same element with a different mass (different number of neutrons). Usually there is one common (abundant) isotope and one or more rare isotopes. E.g. carbon exists as carbon 12 (regular carbon), carbon 13 (one more neutron than carbon 12) and carbon 14 (radiocarbon, two more neutrons than carbon 12). Radiocarbon is radioactive, which means that it is unstable and decays with a half-life of about 5600 years. Isotopes are often reported in delta values, e.g. δ13C = (R/Rstd-1)*1000 for carbon 13, which have units of permil (‰), where R=13C/12C is the ratio of carbon 13 over carbon 12 of the sample and Rstd is the ratio of a reference standard. Isotope delta values can change due to fractionation.

    Jet Stream

    Fast westerly winds in the upper atmosphere at subtropical latitudes, caused by the Coriolis force acting on the upper branch of the Hadley circulation.


    Joule is the SI unit of energy or work. 1 J = 1 kg m2 s-2.

    Kinetic Energy

    Energy due to movement of an object. The kinetic energy of an object is equal to one half its mass times its velocity squared.

    Land Use Change

    Humans' effects on the climate system through modifications of the land surface e.g. through deforestation and agriculture.

    Land-Sea Contrast

    Temperature changes over land are usually larger than over the ocean. There are two main reasons for this: 1) in a transient situation (non-equilibrium) the larger heat capacity of the ocean delays ocean temperature changes compared to land, and 2) evaporative cooling is limited by the availability of water on land, whereas it is not limited over the ocean.

    Lapse Rate

    Rate of temperature decrease with height in the troposphere ΔT/Δz. On average the lapse rate is ~6.5 K/km, which is close to the moist adiabatic lapse rate. A dry atmosphere would have a lapse rate of ~10 K/km.

    Last Glacial Maximum

    The height of the last ice age, about 20,000 years ago. Large ice sheets covered parts of North America and northern Europe, sea-level was 120 m lower than it is today, the air was dustier, and the vegetation distribution was much different from today in many regions.

    Latent Heat

    Energy required for a phase change. E.g. to evaporate 1 g of water 2,300 J is required. The same amount of energy is released during condensation.

    Marginal Benefit

    The additional satisfaction or utility that a person receives from consuming an additional unit of a good or service. A person's marginal benefit is the maximum amount he is willing to pay to consume that additional unit of a good or service.

    Marginal Private Cost

    The private cost of an additional unit of output of a good experienced by an individual firm. Does not include external costs (the social or environmental costs which may arise from the production of a good).

    Marginal Social Cost

    The total cost society pays for the production of another unit. The total cost of the production includes costs to others and the environment as a whole. MSC is calculated as marginal private cost plus marginal external cost (the cost of externalities).



    Meridional Overturning Circulation

    Deep ocean circulation driven mostly by density differences.


    reducing carbon emissions in order to lessen their negative impacts


    Climate models are based on conservation equations for energy, mass, momentum, water, salt, carbon, and other substances. The simplest climate model is the zero-dimensional (0D) Energy Balance Model (EBM), which solves just one equation for the global average surface temperature. Slightly more complex models are 1D EBMs and 1D (vertical) radiative convective models. Intermediate complexity models are e.g. 2D EBMs. The most comprehensive are General Circulation Models (GCMs).


    Tilt in Earth’s axis with respect to Earth’s orbit around the sun. Varies at ~40,000 year cycle.


    Not transparent. A medium is opaque if radiation cannot pass readily through it. Earth’s atmosphere is opaque to terrestrial radiation.


    O3 is a radiatively active molecule in Earth’s atmosphere. It occurs mainly in the stratosphere where it absorbs ultraviolet radiation.

    Ozone hole

    Lack of O3, particularly over the Antarctic, caused by anthropogenic emissions of chlorofluorocarbons (CFCs) that were used as cooling agents in refrigerators and in spray cans.


    Changes in climate before the instrumental record began ~100 years ago.

    permil or ppt

    parts per thousand (‰).


    Process by which plants (including algae) turn CO2 and water into organic matter and oxygen using light as the energy source. It is the reverse chemical reaction of respiration.

    Polar Amplification

    Climate changes at high latitudes are larger than at low latitudes. One reason for this is the ice-albedo feedback, which amplifies climate changes at the poles. Another reason is more latent heat transport from the tropics towards higher latitudes in a warmer climate.

    Polar amplification

    Substance with harmful effects put into the environment by humans.


    Parts per billion.


    Parts per million.


    Wobble of Earth’s axis with respect to its orbit around the sun. Varies at ~20,000 year cycles.


    rain, hail or snowfall


    A statement of fact or value offered in support of a conclusion – we also might think of this as “evidence” for a given position.


    A prescriptive statement is one suggesting we ought or ought not do something, as opposed to a descriptive statement that merely describes the facts of the matter.


    Projections are predictions of future climate changes assuming specific scenarios for future anthropogenic radiative forcings such as the emissions or concentrations of greenhouse gases.


    Surrogates for climate variables used in paleoclimate research. E.g. pollen can be used to reconstruct past vegetation cover, which allows inferences on temperature and precipitation.


    Electromagnetic radiation are waves of electric and magnetic fields that travel through vacuum (space) and matter (atmosphere, ocean). Important for Earth’s climate is radiation from the sun, also called solar, or shortwave radiation FSW, which is at shorter wavelengths (in the visible, ultraviolet and near infrared parts of the spectrum) than the radiation emitted from Earth. The latter is called terrestrial, thermal, or longwave radiation (FLW).

    Radiative Forcing

    (ΔF) Changes in energy fluxes F (in W/m2) at the top-of-the-atmosphere that cause climate change. It is defined as positive (negative) if it leads to warming (cooling). The radiative forcing for a doubling of CO2 is ΔF2xCO2 = 3.7 W/m2. Other examples are increased solar radiation (positive), increased aerosols (negative) or increased surface albedo (negative), e.g. due to land use changes.


    Bounces off something.

    Relative humidity

    (rh = q/qsat) the amount of water in the air (specific humidity q) relative to its temperature dependent saturation value qsat. It is typically reported in percent. E.g. if air at 30ºC has a specific humidity of q = 15 g/kg its relative humidity is approximately rh = 15/30 = 50% since the saturation specific humidity is ~30 g/kg (see Figure 16 in Chapter 4).


    Coarse resolution means that details are not apparent, whereas fine resolution depicts more details, both in space and time. E.g. a coarse resolution climate model does not represent spatial details of the real world. A high-resolution paleoclimate record can depict details in time of climate variations at a certain location.


    Bacteria, fungi, animals, and humans respire organic carbon by oxidizing it. This releases energy and produces water and carbon dioxide. It is the reverse chemical reaction of photosynthesis.


    The amount in grams (g) of salt per kilogram (kg) of sea water. Typical values in the open ocean are around 30-40 g/kg. Other often used and equivalent units are permil (‰) and practical salinity units (PSU): 1 g/kg = 1 ‰ = 1 PSU. Salinity influences the density of sea water such that it becomes denser the saltier it is.

    Sea ice

    Frozen sea water that swims of the ocean’s surface. During the freezing process, much of the salt originally contained in the sea water is trapped in brain pockets and eventually lost by flowing slowly down through channels into the underlying water. Therefore, sea ice is almost fresh water with a salinity of only about 5 permil.

    Sensible Heat

    Heat can be transferred by an air or water parcel with a warmer temperature moving to a place where it is colder. This is called sensible heat flux.


    Characterized by a lack of regard for the moral or legal standards in the local culture. There is a marked inability to get along with others or abide by societal rules.

    Sound Conclusions

    The conclusion of an argument that both follows directly from the premises or evidence provided, and that has only true premises.

    Specific humidity

    the amount of water vapor (in grams) per kilogram of moist air.

    Stefan-Boltzmann Law

    See Blackbody


    Layering of the ocean or atmosphere according to density. Stable stratification has light fluid on top of heavy fluid. If heavy fluid is on top of light fluid the stratification is unstable and convection will occur.


    Region of Earth’s atmosphere, between about 10 and 50 km altitude, where temperatures increase with height. Holds about 20% of Earth’s atmospheric mass.

    T (Temperature)

    Temperature. International units are Kelvin (K) and degrees Celsius (centigrade). In the U.S. Fahrenheit (F) is used. To convert use T[°F] = T[°C]*9/5 + 32 and T[°C] = T[K] - 273.15

    t (Time)

    Time (units are seconds).

    Thermohaline Circulation

    (aka Meridional Overturning Circulation) Density driven (deep) ocean circulation. Temperature (thermo) and salinity (haline) of sea water determine its density. Waters sink from the surface to the deep ocean only at a few places (in the North Atlantic and in the Southern Ocean around Antarctica) where it is dense enough. From there they flow into the interior of the oceans forming a global system of currents.

    Trade Winds

    Easterly (blowing from east to west) surface winds in the tropics.


    Passing through something. E.g. most shortwave radiation is transmitted through the atmosphere, whereas most longwave radiation is absorbed by the atmosphere.


    A medium is transparent if radiation passes through it. E.g. Earth’s atmosphere is mostly transparent to solar radiation.


    Region in Earth’s atmosphere between the troposphere and stratosphere where temperatures do not change with height.


    Lower (~10 km) part of Earth’s atmosphere. Temperatures decrease with height in the troposphere. The troposphere includes most (about 2/3) of the mass of the entire atmosphere.


    Answers to the most basic questions in philosophy – what is this world, what are humans, what is the relationship between this world and humans – constitute a person’s or a group’s worldview.



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