Throughout this User Guide and Climate Futures, you will encounter a number of terms. The following terms are common to all three user modes.
Climate Future
A Climate Future is the description of a plausible future climate, both qualitative (for example: warmer and wetter) and quantitative (for example: 10 of 18 models agree), as described by the combination of two climate variables, for a particular time period and greenhouse gas scenario. Climate futures can be assigned a model consensus rating based on the proportion of climate models that fall within the climate future. In Future Climate (previously ‘Basic’) Mode, climate futures are always described by the combination of annual-average surface temperature change and annual-average rainfall change. In Advanced Mode, these variables can be modified.
Climate variables
Variable | Units of change | Notes |
Surface temperature | °C | Mean temperature as measured at 2 m above the ground |
Maximum temperature | °C | Mean daily maximum temperature as measured at 2 m above the ground |
Minimum temperature | °C | Mean daily minimum temperature as measured at 2 m above the ground |
Rainfall | %* | Mean rainfall |
Heavy rainfall | %* | 99th percentile mean daily rainfall: equivalent to the average of the four wettest days in a year, two wettest days in 6-months, etc. |
Dry days | %* | Mean number of days with <1 mm rainfall |
Relative humidity | %* | Mean relative humidity as measured at 2 m above the ground |
Potential evapotranspiration | %* | Wet Areal Potential Evapotranspiration calculated according to Morton (1983) |
Solar radiation | %* | Surface downward shortwave radiation (equivalent to ‘global radiation’): a commonly used measure in agriculture and energy applications. |
Wind speed | %* | Mean wind speed, calculated from eastward and northward components at 10 m above the ground |
Strong wind | %* | 99th percentile mean daily wind speed: equivalent to the average of the four windiest days in a year, two windiest days in 6-months, etc.. |
Greenhouse Gas Scenario
Climate Futures provides projections based on the climate models used for the Intergovernmental Panel on Climate Change’s Fourth Assessment Report (AR4) as well as those used for the Fifth Assessment Report (AR5) released in 2013. Projections based on the AR4 models (also called the CMIP3 models) can be generated for three greenhouse gas scenarios as described below (for further information, see the Special Report on Greenhouse gas scenarios (Nakićenović and Swart, 2000; sometimes called the SRES). Note that projections based on the AR5 models (CMIP5) use a new set of future greenhouse gas concentration scenarios called Representative Concentration Pathways (refer to the glossary entry for more detail).
A1B The A1B greenhouse gas scenario is a specific case within the A1 scenario. The A1 storyline describes a future world of very rapid economic growth, a global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. The A1 storyline develops into three scenario groups that describe alternative directions of technological change in the energy system. They are distinguished by their technological emphasis: fossil intensive (A1FI), non-fossil energy sources and technologies (A1T), or a balance across all sources (A1B) (where balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end use technologies).
B1 The B1 storyline describes a convergent world with the same global population as in the A1 storyline (one that peaks in midcentury and declines thereafter) but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.
A2 The A2 storyline describes a very heterogeneous world. The underlying theme is self reliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in continuously increasing population. Economic development is primarily regionally oriented and per capita economic growth and technological change more fragmented and slower than other storylines.
Key Climate Futures
A subset of the projected climate futures for a given location, classifying variables, time-period and greenhouse gas scenario that are the most important for decision making. These are usually described as “Best Case”, “Worst Case” and “Most Likely Case”. See also Climate Future.
The following ‘key climate futures’, which are often relevant to risk assessments, are referred to in the Advanced user training.
Most Likely Case
Of the climate futures projected (for a given location, classifying variables, time period and greenhouse gas scenario), the Most Likely Climate Future is that represented by the greatest number of climate models. It must be remembered, however that the climate that does eventuate could lie outside the range of climates projected by any of the climate models used in Climate Futures.
Least Change Case
Of the climate futures projected (for a given location, classifying variables, time period and greenhouse gas scenario), the Least Change Climate Future is that which is closest to the current (1980 – 1999) climate in terms of the selected variables.
Best Case
Of the climate futures projected (for a given location, classifying variables, time period and greenhouse gas scenario), the Best Case climate future is that which would result in the most positive (or least negative) impacts on the system being assessed. For example, in an assessment of the possible impacts of changing climate on mosquito-borne diseases, the climate future with the least increase in temperature and a decrease (or least increase) in rainfall is likely to represent the Best Case. Choosing the Best Case climate future requires a good understanding of the system being studied.
Worst Case
Of the climate futures projected for a given time period and greenhouse gas scenario, the Worst Case Climate Future is that which would result in the most negative (or least positive) impacts on the system being assessed. For example, in an assessment of the possible impacts of changing climate on mosquito-borne diseases, the climate future with the greatest increase in temperature and the greatest increase (or least decrease) in rainfall is likely to represent the Worst Case. Choosing the Worst Case climate future requires a good understanding of the system being studied.
Lower Likelihood, Potentially High Impact
Of the climate futures projected for a given time period and greenhouse gas scenario the lower likelihood potentially high impact are the largest changes in temperature and rainfall that are projected. These could represent a best case and/or a worst case depending on the impacts on the system being assessed.
Representative Concentration Pathways
Climate Futures provides projections based on the climate models used for the Intergovernmental Panel on Climate Change’s Fourth Assessment Report (AR4) as well as those that will be used for the Fifth Assessment Report (AR5) due for release in 2015. Projections based on the AR4 models (also called the CMIP3 models) can be generated for three greenhouse gas scenarios (for more detail see the Greenhouse gas scenarios glossary entry above). Projections based on the AR5 models (CMIP5) use a new set of future greenhouse gas concentration scenarios called Representative Concentration Pathways, or RCPs.
The Representative Concentration Pathways (RCP) are based on selected scenarios from four modelling teams working on integrated assessment modelling, climate modelling, and modelling and analysis of impacts (van Vuuren et al. 2011). Unlike the earlier (SRES) greenhouse gas scenarios, the RCPs are not new, fully integrated scenarios (i.e., they are not a complete package of socioeconomic, greenhouse gas, and climate projections). They are consistent sets of projections of only the components of radiative forcing (the change in the balance between incoming and outgoing radiation to the atmosphere caused primarily by changes in atmospheric composition) that are meant to serve as input for climate modelling. Conceptually, the process begins with pathways of radiative forcing, not detailed socioeconomic narratives or scenarios. Central to the process is the concept that any single radiative forcing pathway can result from a diverse range of socioeconomic and technological development scenarios. Four RCPs were selected, defined and named according to their total radiative forcing in 2100 (see table below).
RCP 8.5 | Rising radiative forcing pathway leading to 8.5 W/m² in 2100. |
RCP 6 | Stabilization without overshoot pathway to 6 W/m² at stabilization after 2100 |
RCP 4.5 | Stabilization without overshoot pathway to 4.5 W/m² at stabilization after 2100 |
RCP 2.6 | Peak in radiative forcing at ~ 3 W/m² before 2100 and decline |
Climate Futures allows exploration of all four RCPs.
Time Period
Climate Futures allows you to explore projections for up to 13 future time periods, in 10 year increments from 2030 to 2090, depending on the greenhouse gas scenario selected.