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The future is uncertain, and we don’t know exactly what it will look like. The main causes are: not knowing how greenhouse gas emissions may evolve in the future, how models simulate natural climate variability (known as internal variability) and inter-model differences.
Emissions scenarios allow us to view different ‘what if?’ questions to help us plan for the future.
Human activity is causing climate change but we don’t know exactly how humans will behave and how emissions of greenhouse gases will change in the future.
Emissions scenarios help us understand a range of potential futures based on different amounts of greenhouse gases.
The emissions scenarios that are currently in use on ClimateData.ca are called Representative Concentration Pathways, or RCPs.
They appear as three coloured bands in the graphs.
These future pathways show us the different “what if?” results from different combinations of assumptions about:
Population Growth
Economic Activity
Energy Intensity
Socio-economic Development
Land Use Change
Climate Policy
Different combinations of these assumptions lead to different levels of greenhouse gas emissions. These emission scenarios are then used in climate models to simulate the climate response.
RCP 2.6 is the low emissions scenario where we limit human caused climate change. Carbon emissions peak almost immediately and then reduce to near zero before the end of the century.
It would mean an average global temperature increase of 1°C by the end of the century and 1.8°C in Canada.* This is roughly compatible with the goal agreed to in the Paris Agreement.
*compared to a baseline period of 1986-2005
RCP 4.5, a medium emissions scenario, shows us a future where we include measures to limit human-caused climate change.
This scenario requires global carbon emissions to stabilize by end of the century.
In Canada, RCP 4.5 would mean an average temperature increase of 3.2°C by the end of the century.*
*compared to a baseline period of 1986-2005
RCP 8.5, the high emissions scenario, shows us a future where there are few restrictions on emissions. Emissions continue to increase rapidly through this century, and only stabilize by 2250.
In Canada, RCP 8.5 would mean an average temperature increase of 6.3°C by the end of the century.*
*compared to a baseline period of 1986-2005
Past climate information alone is not sufficient to make decisions about the future.
As you can see in most graphs in ClimateData.ca, the future will not look like the past (represented by the grey band).
Since we don’t know exactly how different the future will be from the past, there is no one-size fits all approach when deciding which pathways to select – it depends on a wide range of factors that are specific to the type of project, time horizon, etc.
Over the next 30 years, there is little difference between the RCPs.
However, looking further down the road, the pathway we are on is much less certain, and will depend on decisions Canada and other countries make about reducing emissions and adopting clean technologies.
Because we don’t know exactly how different the future will be, it is important to consider a range of possible future climates using more than one emissions scenario in our planning to address the impacts of climate change.
For more information on the impacts of climate change in Canada, see Canada’s Changing Climate Report.
For any questions about using climate data and information, please contact the Climate Services Support Desk.
The future is uncertain, and we don’t know exactly what it will look like. As explained in our article on model uncertainty, the main causes are: not knowing how greenhouse gas emissions may evolve in the future, how models simulate natural climate variability (known as internal variability) and inter-model differences.
All climate models are mathematical representations of the real climate system. While all climate models use well-established physical principles to simulate the climate, each model uses slightly different approaches, which produce inter-model differences. Each model has different strengths and weaknesses. For example, models may use different spatial scales, which affects how well they represent topography. There is also variation in model parameters (e.g., how clouds are represented in the model).
This graph was produced from an ensemble of 24 different climate models that have been developed by research groups from around the world and then run for 3 different scenarios represented by the shaded areas (blue: RCP 2.6; green: RCP 4.5; red: RCP 8.5).
To explain further, let’s reconstruct our graph from the ground-up focusing first on the High Emissions Scenario, also known as RCP 8.5.
Each scenario is made up of many models. Here is the result from a single climate model, which projects around 10°C of warming by 2100 under a high emissions scenario.
This model projects around 4.5°C of warning by 2100 under a high emissions scenario.
Those were extreme examples at the top and bottom of the range of model outputs. The full ensemble of model results fall somewhere in between.
Unfortunately, there is no “best” model. Each model is a unique and sophisticated mathematical representation of the climate system. Therefore, on ClimateData.ca we use an ensemble of models.
Percentiles are used to help show us where the bulk or majority of the model results fall, and to allow us to ignore the outliers. Model results are also called outputs or simulations, because they are simulating the climate.
To explain, let’s take a closer look at an individual year.
We can identify the “10th percentile” value. That is, 10% of the model simulations are less than, or equal to, this value.
We can also identify the “90th Percentile” value. 90% of the model results are less than, or equal to, this value.
Most of the models fall between the 10th and 90th percentile. We can then calculate the “50th percentile”, or median, where half of the model results are below, half above.
These percentiles can then be calculated for all years.
Now let’s zoom back out to see the entire time series. We can see all models (black lines), the range of models that fall within the 10th and 90th percentiles (light red range), and the ensemble median (red line).
For simplicity, we can remove all the individual models and just show the 10th and 90th percentile range as well as the ensemble median.
This approach is applied to the other two emissions scenarios on ClimateData.ca (green for RCP 4.5 and blue for RCP 2.6) as you will see when exploring any of the data and indices available on ClimateData.ca.
When incorporating climate projections into decision-making, it is important to use a set of climate model results to ensure you are prepared for the range of possible future climates.
See our videos on incorporating climate information into decision-making for more information.
For more information on the impacts of climate change in Canada, see Canada’s Changing Climate Report.
For any questions about using climate data and information, please contact the Climate Services Support Desk.
