Glossary

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.

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.

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.

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 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.

Boundary conditions are values for prognostic variables (e.g. temperature) or fluxes (e.g. heat flux) at the boundary of the model domain needed to solve the interior grid boxes in climate models and other models that use differential equations.

Assigning time to a paleoclimate record.

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.

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.

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.

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

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.

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.

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.

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.

Incoming solar radiation.

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

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.

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.

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.

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.

(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.

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.

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.