California Climate Change Glossary

Letter E

Economic Potential. The portion of the technical potential for GHG emissions reductions or energy-efficiency improvements that could be achieved cost-effectively in the absence of market barriers. The achievement of the economic potential requires additional policies and measures to break down market barriers. (IPCC)

Ecosystem. An ecological community together with its environment, functioning as a unit. The scale of an ecosystem largely depends on the type of study that is conducted and may range from a small number of populations and their environment to the entire earth. (Lenn)

Eddy Mixing. Mixing due to small scale turbulence processes (eddies). Such processes cannot be explicitly resolved by even the finest resolution Atmosphere-Ocean General Ciculation Models currently in uses and so their effects must be related to the larger scale conditions. (IPCC)

El Niño. A climatic phenomenon occurring irregularly, but generally every 3 to 5 years. El Niños often first become evident during the Christmas season (El Niño means Christ child) in the surface oceans of the eastern tropical Pacific Ocean. The phenomenon involves seasonal changes in the direction of the tropical winds over the Pacific and abnormally warm surface ocean temperatures. The changes in the tropics are most intense in the Pacific region, these changes can disrupt weather patterns throughout the tropics and can extend to higher latitudes, especially in Central and North America. The relationship between these events and global weather patterns are currently the subject of much research in order to enhance prediction of seasonal to interannual fluctuations in the climate. (EPA)

Emission. The release of a substance (usually a gas when referring to the subject of climate change) into the atmosphere. (EPA)

Emission Permit. A non-transferable or tradeable allocation of entitlements by a government to an individual firm to emit a specific amount of a substance. (IPCC)

Emission Quota. The portion or share of total allowable emissions assigned to a country or group of countries within a framework of maximum total emissions and mandatory allocations of resources or assessments. (IPCC)

Emissions Scenario. Representation of the future development of emissions of greenhouse gases based on a set of assumptions about driving forces and their key relationships. (Lenn)

Emission Standard. A level of emission that under law may not be exceeded. (IPCC)

Energy Intensity. Ration of energy consumption and economic or physical output. At the national level, energy intensity is the ratio of total domestic primary energy consumption or final energy consumption to gross domestic product or physical output. (IPCC)

Enhanced Greenhouse Effect. The natural greenhouse effect has been enhanced by anthropogenic emissions of greenhouse gases. Increased concentrations of carbon dioxide, methane, and nitrous oxide, CFCs, HFCs, PFCs, SF6, NF3, and other photochemically important gases caused by human activities such as fossil fuel consumption and adding waste to landfills, trap more infra-red radiation, thereby exerting a warming influence on the climate. See Climate Change and Global Warming. (EPA)

Equilibrium Response. The steady state response of the climate system (or a climate model) To an imposed radiative forcing. (IPCC)

Equivalent CO₂. The concentration of CO₂ that would cause the same amount of radiative forcing as a given mixture of CO₂ and other greenhouse gasses. (IPCC)

Evapotranspiration. The sum of evaporation and plant transpiration. Potential evapotranspiration is the amount of water that could be evaporated or transpired at a given temperature and humidity, if there was plenty of water available. Actual evapotranspiration can not be any greater than precipitation, and will usually be less because some water will run off in rivers and flow to the oceans. If potential evapotranspiration is greater than actual precipitation, then soils are extremely dry during at least a major part of the year. (EPA)

External Impacts/Externalities. Impacts generated by climate change (or some other environmental change) that cannot be evaluated by a competitive market because of a lack of information and or the inability to act on the information. (IPCC)

Externalities. By-products of activities that affect the well-being of people or damage the environment, where those impacts are not reflected in market prices. The costs (or benefits) associated with externalities do not enter standard cost accounting schemes. (IPCC)

Extreme Weather Event. A manifestation of weather which is rare within its statistical distribution on a particular location. By rare one usually means rarer than the 90th percentile. The characteristics of extreme weather vary according to the location. (Lenn)