Aerosols are small particles in the atmosphere originating from natural processes and emissions of air pollutants from human activities (e.g., burning fossil fuels). Future climate scenarios are used to help plan for future climate changes. The climate scenario SSP3-7.0 has higher aerosol emissions than the other scenarios on ClimateData.ca. Find out how additional aerosols affect SSP3-7.0 in this article.
Aerosols are small particles in the atmosphere of both natural and human-made origin. How a given aerosol will influence the climate depends on the material it is composed of, its colour, size, and where it is in the atmosphere (i.e., vertical location and whether it is over land or ocean)1. For an introduction to aerosols and climate please visit Aerosols and their Climate Impacts.
Climate models are used to produce future climate projections, which inform preparations and plans for the future. Determining how the climate will change depends on current and future emissions of greenhouse gases and aerosols. The Shared Socio-economic Pathways (SSPs) describe a variety of future development pathways for human societies in the 21st Century, with each pathway describing differing levels of population, technology use, climate policy, mitigation, and socio-economic development. To learn more about the SSPs please visit Understanding Shared Socio-Economic Pathways.
Most SSPs assume medium to strong air pollution control, resulting in reduced amounts of aerosols compared with the present day. Since a warmer atmosphere will have a more active hydrological cycle2 most regions will be wetter in the future compared with today3. In SSP3-7.0, however, aerosol concentrations are higher than those in all other SSPs4,5, describing a hypothetical future where aerosol concentrations increase relative to the present day due to weak air pollutant policies. SSP3-7.0 also assumes high greenhouse gas emissions.
Recently, some researchers have suggested that the upper end climate scenario SSP5-8.5 is unlikely or even implausible, in part because of the successful greenhouse gas emissions reductions that have already occurred6. As a result, SSP3-7.0 has been suggested as an alternative scenario for use in climate impacts and risk assessments, and adaptation planning6.
SSP3-7.0 was designed to enable researchers to better understand the role of aerosols in atmospheric chemistry, particularly the consequences of continued high levels of aerosol concentrations on climate change7. Regardless, it provides a potentially useful scenario for climate change adaptation purposes because it represents less climate change overall than SSP5-8.5, but more than all other available scenarios. SSP3-7.0 is available on ClimateData.ca to give users an alternative future climate scenario with high GHG concentrations. When using this scenario, however, it is important to carefully consider the differences between SSP3-7.0 and the other scenarios, specifically, how the increased aerosol concentrations may affect projections of climate change at the local scale.
Figure 1 shows the relationship between changes in global average temperature and precipitation for the four SSPs available on ClimateData.ca. SSP1-2.6, SSP2-4.5 and SSP5-8.5 have a linear relationship between temperature and precipitation increases. In contrast, SSP3-7.0 shows only a small increase in precipitation compared to SSP2-4.5, despite SSP3-7.0 being much warmer. This is because the higher aerosol concentrations in SSP3-7.0 offset some of the precipitation increases that would otherwise occur from the increased temperatures.
Figure 1: Changes in mean global land surface air temperature (°C) and precipitation (%) for 2071–2100 with respect to 1971-2000. Due to data availability, the data in this figure are from a subset of models in the CanDCS-M6 ensemble. The same 22 models were used for each emissions scenario for consistency. Compared to the CanDCS-M6 ensemble this subset does not include the models CMCC-ESM2, HadGEM3-GC31-LL, KIOST-ESM and TaiESM1). The data points show the average of the models for each SSP (the “ensemble mean”), with the cross showing the 90% confidence interval. The black dashed line indicates the linear relationship between precipitation and temperature change computed from the ensemble averages of SSP1–2.6, SSP2–4.5 and SSP5–8.5 simulations6. SSP3-7.0 has less precipitation than the other scenarios compared with its level of emissions and, as a result, is below the black trend line [Source: Eva Gnegy, Environment and Climate Change Canada].
In contrast to the global correlation, in Canada, SSP3-7.0 follows more closely the near linear relationship between temperature and precipitation (Figure 2). This is because Canada already has relatively good air quality so the differences in aerosol concentrations amongst the scenarios are minor compared with the global average. Consequently, climate change in Canada is not as sensitive to the higher aerosol emissions in SSP3-7.08. As a result, in Canada differences among the SSPs are more directly related to each scenario’s greenhouse gas concentrations rather than to its aerosol concentrations.
Figure 2: Changes in mean Canadian land surface air temperature (°C) and precipitation (%) for 2071–2100 with respect to 1971-2000. The black dashed line shows the linear relationship computed from the ensemble means of SSP1–2.6, SSP2–4.5 and SSP5–8.5 simulations. In Canada, the precipitation increase in SSP3-7.0 shows the same dependence on temperature as in the other scenarios in contrast to the global relationship (Figure 1). [Source: Eva Gnegy, Environment and Climate Change Canada]
