Glossary

Adaptive capacity

The ability of systems, institutions, humans, and other organisms to adjust to potential damage, to take advantage of opportunities, or to respond to consequences.

Bias correction

Various techniques applied to global and/or regional climate model outputs to adjust for systematic errors (or biases). For example, a bias adjustment can be applied to model output which underestimates extreme precipitation events, or temperatures that are consistently too high. There are several sources of model biases that bias adjustment can adjust for, including spatial resolutions that are not fine enough to resolve all types of weather phenomena, or because model formulations rely on simplifications of physical processes.

Climate Adaptation

Climate adaptation: In human systems, the process of adjustment to actual or expected climate and its effects to moderate harm or exploit beneficial opportunities. In natural systems, the process of adjustment to actual climate and its effects. Human intervention may facilitate adjustment to expected climate and its effects.

Climate model

A numerical representation of the climate system based on the physical, chemical, and biological properties of its components, their interactions, and feedback processes and accounting for some of its known properties. Climate models are applied as a research tool to study and simulate long-term climate projections (decadal or longer) and operationally used to create shorter climate predictions (seasonal, annual, interannual).

Climate projection

A climate projection is a simulation of Earth's climate in the future and how it responds to changes in greenhouse gas concentrations, aesosols emissions, and changes in land use. Rather than representing a prediction of the most likely future, climate projections estimate general future conditions, based on assumptions about future future socioeconomic and technological developments that may or may not be realized.

Climate sensitivity

The change in the surface temperature in response to a change in the atmospheric carbon dioxide concentration or other radiative forcing.

CMIP5

CMIP5 stands for the Coupled Model Intercomparison Project, Phase 5. According to the World Research Climate Programme, the Coupled Model Intercomparison Project (CMIP) aims "to better understand past, present and future climate changes arising from natural, unforced variability or in response to changes in radiative forcing in a multi-model context. This understanding includes assessments of model performance during the historical period and quantifications of the causes of the spread in future projections." In other words, CMIP studies the extent to which climate models agree with one another and evaluates reasons for any disagreement. Performance is compared across models by running each model with a standard protocol and set of assumptions.

CMIP6

The Coupled Model Intercomparison Project, Phase 6 (CMIP6) is a collaborative climate modeling effort overseen by the World Climate Research Programme's Working Group on Climate Modeling, with the goal of producing climate model output with consistent standards in areas such as variable naming and experimental design. This consistency allows different models to be compared to each other more easily. CMIP6 is the latest generation of global climate models (circa 2020) and is used in efforts such as the Intergovernmental Panel on Climate Change Sixth Assessment Report (IPCC AR6) and the Fifth National Climate Assessment (NCA5).

Community Climate System Model (CCSM)

The Community Climate System Model (Version 4) developed by the University Corporation for Atmospheric Research.

Cooling Degree Days (CDD)

A cooling degree day (CDD) is the number of degrees by which a daily average temperature exceeds a reference temperature and may therefore require additional energy for space cooling. The reference temperature is typically 65 degrees Fahrenheit, although different utilities and planning entities sometimes use different reference temperatures. The reference temperature loosely represents an average daily temperature below which space cooling (e.g. air conditioning) is not needed. The average temperature is the average of the minimum and maximum daily temperatures. CDDs can be summed over the entire year or over a portion of the year (e.g. the month of July) as a rough indicator of cooling energy used over that period.

Daily Precipitation

Daily precipitation measures the amount of precipitation that occurs on a single day for a climate model, which are then used to calculate seasonal or annual average daily precipitation estimates. These estimates include the average daily rainfall (the typical rainfall on any day for that season) and the maximum daily rainfall (the largest amount of rainfall in a single day for that season).

Degree Days

Degree days measure how cold or warm a location is by comparing the daily average temperature to a reference temperature, usually 65°F (18.33°C). Heating or cooling degree days roughly correlate with building heating or cooling needs, providing a simple useful estimate in energy planning.

Downscaling

A method that derives local- to regional-scale information from larger-scale models or data analyses. Two main methods exist: dynamical downscaling and empirical/statistical downscaling. The dynamical method uses the output of regional climate models, global models with variable spatial resolution, or high-resolution global models. The empirical/statistical methods are based on observations and develop statistical relationships that link the large-scale atmospheric variables with local/regional climate variables. In all cases, the quality of the driving model remains an important limitation on quality of the downscaled information. The two methods can be combined, for example, applying empirical/statistical downscaling to the output of a regional climate model consisting of a dynamical downscaling of a global climate model.

Drought

An exceptional period of water shortage for existing ecosystems and the human population (due to low rainfall, high temperature and/or wind).

Dynamical downscaling

Dynamical downscaling applies the outputs of a GCM as inputs to a separate, high-resolution regional climate model. Dynamical downscaling accounts for the physical processes and natural features of a region, as well as the complex interaction between these elements and global dynamics under a climate scenario.

Emissions scenarios

An emissions scenario is a representation of future greenhouse gas emissions and resulting atmospheric concentrations through time. An emissions scenario illustrates a plausible future so that climate projections for that emissions scenario can be generated, used to inform analysis and decision-making, and compared to other scenarios.

End-Century

"End-century" on ClimRR refers to a ten year period between 2085-2094, for which future climate projections have been modeled.

Ensemble (modeling)

A collection of comparable datasets that reflect variations within the bounds of one or more sources of uncertainty and that, when averaged, can provide a more robust estimate of underlying model behavior. Ensemble techniques are used by the observational, reanalysis, and modeling communities.

Ensemble member

A single simulation or GCM run within a larger set of simulations (referred to as an ensemble) that are generated to model future climate. Each ensemble member is typically produced by slightly varying the initial conditions or model parameters, or by using different models altogether. Using multiple ensemble members helps account for the natural variability of the climate system and the uncertainties inherent within model predictions.

Extreme events

A weather event that is rare at a particular place and time of year, including, for example, heatwaves, cold waves, heavy rains, periods of drought and flooding, and severe storms. Definitions of "rare" vary and the characteristics of what is called extreme weather may vary from place to place.

Extreme heat

Temperatures that are much hotter and/or humid than average. Because some places are hotter than others on average, the definition of extreme heat depends on what is considered typical for a particular location at that time of year.

Extreme Precipitation Event

An extreme precipitation event is a weather event where precipitation (rain, snow, hail, etc.) is of a high ("extreme") magnitude and greatly exceeds typical weather for a location and place. There is no single definition of what constitutes the threshold above which a precipitation event is considered "extreme." Precipitation events can be extreme in their duration, maximum precipitation rate, total volume of precipitation delivered, or a combination of these three factors. Often, extreme precipitation events are identified based on their return period.

Extreme value analysis

A statistical approach used to quantify the behavior of a variable during events that deviate substantially from the mean. It typically involves analyzing annual maxima or minima, or values that exceed a certain threshold, to approximate the magnitude and probable return period of extreme intensities. EVA is widely applied in fields like climate and hydrology to understand the occurrence of an extreme weather event and commonly uses specialized distributions like the Generalized Extreme Value (GEV) distribution.

Fire Weather Index (FWI)

The Canadian Fire Weather Index (CFWI), or just Fire Weather Index (FWI), estimates wildfire danger using weather conditions that influence the spread of wildfires. The FWI is comprised of multiple components that are developed using daily readings of temperature, relative humidity, wind speed, and 24-hour precipitation. This weather information is used to estimate the total fuel available for combustion (dry organic material) and the rate of fire spread. The FWI is useful for evaluating weather-based conditions that heighten the danger of wildfire spread once ignition has occurred; it does not account for sources of ignition, which can have both natural and human causes.

Flash Flood

A flood caused by heavy or excessive rainfall in a short period of time, generally less than six hours. Flash floods can occur within minutes or a few hours of excessive rainfall.

Forcing

A change or impact to a factor that affects Earth's climate.

Generalized Extreme Value (GEV) distribution

A family of continuous probability distributions developed within extreme value theory to model the largest or smallest value from a large collection of random observations. The GEV distribution is used to model the behavior of extreme events, such as the highest or lowest temperatures, maximum wind speeds, or the most intense rainfall within a given period. The GEV distribution is characterized by location, scale, and shape parameters, and combines the probability distributions of the Gumbel, Fréchet, and Weibull distributions through a continuous shape parameter that determines the tail behavior.

Geophysical Fluid Dynamics Laboratory (GFDL)

The Earth System Model Version 2G developed by the Geophysical Fluid Dynamics Laboratory at the National Oceanic and Atmospheric Administration (note: the general convention, which we use, is to use the Laboratory's abbreviation to identify this model).

Global Climate Model (GCM)

A global climate model (GCM) is a complex representation of the major climate system components (atmosphere, land surface, ocean, and sea ice) and their interactions. These models project climatic conditions at frequent intervals over long periods of time (e.g., every 3 hours for the next 50-100 years), often with the purpose of evaluating how one or more GHG scenarios (such as RCP4.5 or RCP8.5) will impact future climate.

Global mean sea level (GMSL)

The average of relative sea level or of sea surface height across the ocean.

Greenhouse gas (GHG)

Natural and human-caused gases that absorb and emit radiation and amplify the greenhouse effect. Water vapor, carbon dioxide, nitrous oxide, methane, and ozone are the primary GHGs in Earth's atmosphere. Other GHGs include sulfur hexafluoride, hydrofluorocarbons, chlorofluorocarbons, and perfluorocarbons.

HadGEM

The Hadley Global Environment Model 2-Earth System developed by the United Kingdom's Met Office.

Harden (infrastructure)

Hardening infrastructure means making infrastructure more resilient in the face of extreme events (such as hurricanes, tornadoes, and earthquakes) and other disasters, both natural and human-made.

Hardiness zones (plants, agriculture)

10°F geographic bands based on the annual lowest winter temperature in a particular location, averaged over a period of years. They serve as a standard by which gardeners and growers can determine which plants are most likely to thrive at a location.

Hazard Mitigation

Any sustained action taken to reduce or eliminate the long-term risk to human life and property from hazards.

Heat index

Heat Index describes how heat is perceived, based on temperature and relative humidity. Heat index can better capture heat-related risks than temperature alone.

Heating Degree Day (HDD)

A heating degree day (HDD) is the number of degrees by which a daily average temperature is below a reference temperature and may therefore require space heating. The reference temperature is typically 65 degrees Fahrenheit, although different utilities and planning entities sometimes use different reference temperatures. The reference temperature loosely represents an average daily temperature above which space heating is not needed. The average temperature is the average of the minimum and maximum daily temperatures. HDDs can be summed over the entire year or over a portion of the year (e.g. the month of January) as a rough indicator of heating energy over that period.

Intergovernmental Panel on Climate Change (IPCC)

An intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities.

Internal variability

Internal variability represents the natural (stochastic) variations in the Earth's climate, due to interactions between the atmosphere, ocean, land surface, and sea ice. In global climate models with multiple simulations, this uncertainty can result in slightly different outputs based on small differences in the model's physical processes design. For example, the timing of events such as the El Niño pattern in the Pacific Ocean may vary between simulations, depending on the global climate model's parameterization.

Invasive species

A species that is not native to a specific location or nearby, lacks natural controls, and tends to rapidly increase in abundance, displacing native species. Invasive species may also damage the human economy or human health.

Lack of Precipitation

Each climate model estimates an amount of precipitation (whether rain, snow, sleet, or ice) that occurs every 3 hours across the modeled period. These 3-hour precipitation estimates were used to identify days in which no precipitation occurred (i.e., the total daily precipitation quantity equaled zero). Using this information, Argonne calculated the greatest number of consecutive days in which no precipitation occurred for each year in a scenario. This process was repeated for each year in a scenario in order to identify the maximum value (e.g., the decadal maximum) for each climate model, which were averaged to estimate the ensemble mean of the highest number of consecutive days without precipitation in a single year.

Mid-Century

"Mid-Century" data on ClimRR refers to modeling conducted across a ten-year period between 2045-2054. One of two emissions scenarios (RCP4.5 or RCP8.5) are used to model this future period.

Model uncertainty

Uncertainty about climate response to a particular scenario that arises from design differences between models. Global climate models are developed by different research institutions and differ in how they represent the global climate system. While these are sophisticated tools, they each simulate the climate in a unique way and may produce different responses to the same set of forcings. Using multiple climate models can help understand where there is consensus and where models suggest different potential futures.

Precipitation

Precipitation is any form of water, whether liquid or solid, that forms in the atmosphere and falls to Earth's surface. This includes rain, drizzle, sleet, hail, and snow. ClimRR's 12km precipitation projections are based on modeling at a 3-hour timestep, capturing total precipitation over each 3-hour period.

RCP4.5

Described by the IPCC as an intermediate scenario. Emissions in RCP4.5 peak around 2040, then decline.

RCP8.5

In this scenario, emissions continue to rise throughout the 21st century. This scenario is the highest emissions scenario modeled by the IPCC.

Relative humidity

A measure of how much moisture (water vapor) is in the air compared to the maximum amount the air can hold at a given temperature. It's expressed as a percentage.

Relative sea level

The height of the sea surface, measured with respect to the height of the land at a particular location. Relative sea level changes in response to both changes in the height of the sea surface and changes in the height of the underlying land.

Representative Concentration Pathways (RCPs)

A Representative Concentration Pathway (RCP) is a representation of a plausible greenhouse gas (GHG) concentration trajectory through time. The pathways describe different scenarios through which GHG emissions, as well as changes in land use and land cover, lead to various concentrations of GHGs in the atmosphere over time. emitted in the years to come. Common RCPs include RCP2.6, RCP4.5, RCP6.0, and RCP8.5, with higher numbers signifying greater concentrations of GHGs.

Resilience

The ability to prepare for threats and hazards, adapt to changing conditions, and withstand and recover rapidly from adverse conditions and disruptions.

Return Period

The average time interval between occurrences of a particular event, such as flood or extreme temperature, that is equaled or exceeded. For example, a 100-year return period refers to an event that has a 1% chance of occurring in any given year.

Risk

Threats to life, health, and safety, the environment, economic well-being, and other things of value. Risks are evaluated in terms of how likely they are to occur (probability) and the damages that would result if they did happen (consequences).

Risk assessment

Studies that estimate the likelihood of specific sets of events occurring and their potential positive or negative consequences.

Runoff

The flow of water over the surface or through the subsurface, which typically originates from the part of liquid precipitation and/or snow/ice melt that does not evaporate, transpire, or refreeze and returns to water bodies.

Shared Socioeconomic Pathways (SSPs)

Shared Socioeconomic Pathways (SSPs) are pathways that describe alternative futures of socioeconomic development, modeling features such as political, economic, and other societal dynamics and choices which impact greenhouse gas emissions, anthropogenic aerosol generation, and land use changes. Shared Socioeconomic Pathways are used to link socioeconomic scenarios to potential emissions trajectories, as represented by "Representative Concentration Pathways'' (RCPs), in order to provide a useful integrative frame ffor climate impact and policy analysis. Commonly used SSPs include SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5.

Storm surge

The temporary increase, at a particular locality, in the height of the sea due to extreme meteorological conditions (low atmospheric pressure and/or strong winds). Storm surge is most noticeable during large tropical storm or cyclone events.

Temperature

Temperature is a measure of hotness or coldness on a given scale, usually Fahrenheit or Celsius (we use Fahrenheit on ClimRR). Average temperatures - over months, seasons, or years - provide a broad picture of how hot or cold a place is and its general habitability.

Temperature Maxiumums

The maximum average temperature is calculated using the highest daily near-surface temperature reading, which typically occurs at midday or the afternoon. These values are used to provide annual and seasonal estimates of average high temperatures.

Temperature Minimums

The minimum average temperature is calculated using the lowest daily near-surface temperature reading, which typically occurs at night. These values are used to provide annual and seasonal estimates of the average low temperatures.

Total Precipitation

Total precipitation measures cumulative precipitation over a given span of time, whether annual, seasonal, or monthly.

Vapor pressure deficit (VPD)

The difference between how much moisture is in the air and the amount of moisture in the air at saturation (i.e., at 100% relative humidity). Vapor pressure deficit can be used to evaluate drought-like conditions.

Watershed

An area of land that drains water to a particular stream, river, lake, bay, or ocean.

Wildland-urban interface (WUI)

The line, area, or zone where structures and other human development meet or intermingle with undeveloped wildland or vegetation.

Wind Speed

Wind speed describes the rate at which air is moving horizontally past a given point. In ClimRR, average wind speeds are derived using wind speeds modeled at a 3-hour timestep, with instantaneous measures of wind at each 3-hour interval.