Glossary

Anthropogenic: environmental change caused or influenced by people, either directly or indirectly. Natural boundary values, or climate forcings of a climate simulation would include, but are not limited to, changes in volcanic aerosol concentrations, solar insolation cycles, and sea surface temperatures. Human-influenced, also called “anthropogenic”, boundary value variables would include changes in greenhouse gas concentrations and alterations of land surfaces.

AOGCM (Atmosphere-Ocean GCM)

Bias Biases in climate models are errors when compared to observations. They can be caused by a range of factors due to limited spatial resolution (large grid sizes), simplified thermodynamic processes and physics or incomplete understanding of the global climate system.

Bias-Correction Spatial Downscaling (BCSD) Method Corrected for AOGCM biases, and generated model data with high spatial resolution from the original coarser resolution AOGCM data. References: Wood et al. 2002 http://gdo-dcp.ucllnl.org/downscaled_cmip3_projections/dcpInterface.html See An Introduction to the Downscaled Climate and Hydrology Projections Website for two related videos on how to access downscaled climate and hydrology projections on this site.

Boundary value: a data value that corresponds to a minimum or maximum input, internal, or output value specified for a system or component. With climate models, boundary values are increasingly important. The term “boundary values” is used to describe the factors that serve to limit the possible outcomes in a system. When we are considering years, decades, and centuries into the future, we are talking about the projection end of the spectrum, where boundary values are more important than initial values.

Climate: the long-term weather pattern in a region, typically averaged over 30 years. It is sometimes said, “Climate is what you expect, weather is what you get.” Climate is the statistical representation of weather over days, months, seasons, years, decades and longer.

Climate change scenarios: plausible climate futures, taking into account increasing atmospheric concentrations of greenhouse gasses, and usually constructed from computer-based models of the Earth-Ocean-Atmosphere system. Describes a set of possible mean characteristics of a future climate; for example, hotter and wetter. The emissions scenarios are the driving force, or cause; the climate change scenarios capture the effect. So an example of an emissions scenario would be: CO2 concentration will increase to 550 parts per million, (ppm) by 2050 and 700 ppm by 2100—as shown in the middle emisions scenario on the left. A corresponding climate change scenario would be: global mean temperature will increase steadily by 2°C by 2050 and almost 3°C by 2100.

Climate Forcings: factors that cause physical processes affecting the climate on the Earth (examples: solar radiation, albedo, greenhouse gasses, temperature) describe the physical states of the Earth-atmosphere-ocean system that are prescribed to simulate natural and human-influenced processes. CMIP A collaborative framework designed to improve knowledge of climate change by standardizing global climate model (GCM) experiments and model output, comparing/evaluating GCMs, and make GCM data publicly available. “Coupled” refers to the interconnected components of the climate system (i.e., land, air, water, etc.) that are simulated by the climate models; “intercomparison” references the many models that are available to compare with observations and to one another to characterize model uncertainty and scenario uncertainty. The CMIP project started in 1995 and has multiple versions, including CMIP3 (2005), CMIP5 (2011), and CMIP6 (2018) - there was no CMIP4.

Emission Scenarios: possible pathways that society might take in the emission of greenhouse gasses and aerosol concentrations in the future. This refers to storylines of possible future changes in greenhouse gas concentrations in the IPCC reports prior to Assessment Report 5. The different possible changes described by these storylines are often referred to as “pathways.”

ESM - “coupled Earth System Model” or “coupled climate model”, where there are land, cryospheric, atmosphere, and ocean component models. Note the previously-used term “coupled atmosphere-ocean general circulation model”, or AOGCM, which just highlighted the atmosphe and ocean components.

GCM (General Circulation Model, sometimes called Global Climate Model) numerical models representing physical processes in the atmosphere, ocean, cryosphere and land surface

Initial Values - To distinguish weather predictions versus climate projections, we use the terms initial value problem versus boundary value problem. Weather predictions are primarily initial value problems. For example, a Numerical Weather Prediction (NWP) model will use the initial value, based on observed conditions, and predict how those conditions will evolve with time. When we are looking at hours and days we are clearly in the weather prediction end of the spectrum where initial values are highly important. The initial value is represented by the initial states of the climate system, including ocean heat content, and surface snow and ice cover.

IPCC (International Panel on Climate Change)the scientific group assembled by the United Nations to monitor and assess all global science related to climate change

Narratives:Combination of projections and scenarios.

Period Change Approach

Predictions an attempt to produce a most likely description or estimate of the actual evolution of the the future. A weather prediction, or forecast, describes the near-term likelihood of a weather event such as a specific occurrence of rain or snow and/or the expected change in temperature. A weather forecast, for example, might read, “colder with a 70% chance of snow this afternoon.” A climate prediction, on the other hand, might call for below average precipitation and near average temperature over the next 30 days.

Projections: Climate models do predict specific weather events many years into the future, but not with the intention for use as time and site-specific forecasts. Rather, the intended use of climate model output is to generate statistics of weather phenomena, such as means and variability of precipitation or temperature, and thus to characterize the collective impact of weather events. These climate predictions are typically referred to as projections, or simulations, and lack the short-term specificity of weather predictions. Think of the difference between predictions and projections in the following way: Prediction refers to the short-term evolution of a weather system from an initial state under constant boundary conditions. Predictions are associated with probability that can be verified. Projection refers to how the statistical measures associated with a climate system will change in response to changing boundary values. Projections, like predictions, may also be associated with probabilities, but they often cannot be verified in time to provide meaningful feedback to the climate modeling system.

Radiative forcing A measure of how the energy balance of the Earth–atmosphere system is influenced. The word ‘radiative forcing’ is used because these factors change the balance between incoming solar radiation and outgoing infrared (IR) radiation within the Earth’s atmosphere.

RCP (Representative Concentration Pathway) is a greenhouse gas concentration (not emissions) trajectory adopted by the IPCC.

Scenarios: Non-climate potential futures (management options,

Shared Socio-economic Pathways Climate change scenarios of projected socioeconomic global changes as defined in the IPCC Sixth Assessment Report on climate change in 2021. The SSPs are based on five narratives describing broad socioeconomic trends that could shape future society. These are intended to span the range of plausible futures, including: a world of sustainability-focused growth and equality (SSP1); a “middle of the road” world where trends broadly follow their historical patterns (SSP2); a fragmented world of “resurgent nationalism” (SSP3); a world of ever-increasing inequality (SSP4); and a world of rapid and unconstrained growth in economic output and energy use (SSP5).

SRES (Special Report on Emissions Scenarios) scenarios constructed to explore future developments in the global environment with special reference to the production of greenhouse gasses and aerosol precursor emissions

Time Slices

Uncertainty: The degree to which the measured value of some quantity is estimated to vary from the true value.Uncertainty can arise from a variety of sources.

Water Availability: Water available for human and ecosystem use. Includes amount, timing, delivery rates, ….

Weather: the state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloud cover. describes the details of what we experience over the course of hours and days.

XLRM Approach: Robust decision making framework