Ozone and aerosols can influence many of the process-es that lead to the formation of clouds and precipitation events. This can change surface temperature due to the associated influence on forcing, or influence the amount of radiation that reaches the surface, changing evapo-ration. By absorbing sunlight in the atmosphere, O3 and aerosols can change the vertical temperature structure of the air, and thus convection and cloud formation. Aer-osol particles can also act as cloud condensation and ice nuclei, affecting the formation and concentration of cloud particles in both liquid and ice phases. The non-ho-mogeneous aerosol spatial distribution can change wind patterns by altering the regional temperature contrasts that drive the winds, and thus influence where water vapour is distributed and precipitation falls. As these localized effects can influence large-scale atmospheric circulation, they can also affect temperature, cloudiness and precipitation far away from the regions in which the forcing due to aerosols was concentrated.
The impact of global forcing by well-mixed greenhouse gases – mainly CO2 – on rainfall patterns was modelled in IPCC AR5 (IPCC, 2013: Chapters 10 and 12) and the results are consistent across models at the global scale and in some regions, such as at high latitudes, where rainfall generally increases as the planet warms. Rainfall also tends to increase near the equator and decrease in the subtropics as the Hadley cell broadens. Some other regional patterns, such as a northward shift in wintertime storm tracks across the North Atlantic, are also fairly consistent across models.
Nonetheless, many of the smaller-scale spatial patterns of rainfall change are inconsistent across models. This applies to most of Latin America and the Caribbean, as discussed previously (Figure 2.1). Furthermore, as changes due to reductions in aerosols and O3 are likely to have distinctly different impacts on regional rainfall, comparison of rainfall changes under the reference scenario with those seen in other models would have only minimal relevance to putting into context the rainfall changes projected under an SLCP mitigation strategy.
These model outputs are yet to be explored by scientists in the context of hydrological models, crop suitability and yield models, dynamic vegetation models or species distribution models. As a result, the sections that follow on the above topics should be read bearing in mind the short-lived and therefore not homogeneously distributed,
having higher concentrations close to the sources of emission, they have a larger impact on forcing close to the regions in which they are emitted.
As mentioned, changes in temperature were cal-culated by three different models: GISS, GEOS-Chem Adjoint and TM5-FASST. The equilibrium temperature response to the changes in forcing was calculated using global and regional temperature potentials (Shine et al., 2005; Shindell and Faluvegi, 2010) that relate forcing to temperature change.
The GISS model was used with global emissions derived from the GAINS model, which incorporates Latin American and Caribbean emissions developed in this assessment, and also recent GAINS emission estimates for all other regions of the world. The result is shown
in Figure 2.2, which illustrates that under the reference scenario emissions, the global temperature will increase by about 1.3oC by 2050 relative to present-day tempera-tures, or 2.3oC above the 1890–2010 temperature. The projected calculations based on the GISS model forcings were made up to 2070, and under the reference scenario, which includes a considerable increase in hydrofluoro-carbon (HFC) emissions, the increase rises to 3oC above the 1890–2010 temperature.
The GEOS-Chem Adjoint and TM5-FASST models were used to estimate the impact of Latin American and Caribbean emissions only on global equilibrium temper-atures – the temperature of the world that would result when it reaches equilibrium at some date in the future.
Figure 2.3 shows the result of applying the GEOS-Chem Adjoint model estimates, indicating that the region’s emissions – from the 2010 reference scenarios – would be expected to lead to a net increase in global temper-ature, but it is important to note that this is a very small change compared to the global temperature change already experienced, or expected by 2050. In 2050, it is projected that the region’s reference scenario emissions will more or less have doubled in their impact on global temperatures compared with 2010, although in absolute terms this is still a very small change in comparison to the overall expected warming from global emissions.
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Figure 2.4
Projected surface temperature change in 2070 relative to 2010, under the IPCC RCP 4.5 and RCP 8.5 scenarios Note: both scenarios are from an ensemble of
five simulations with the GISS-E2R model.
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Figure 2.4
Projected surface temperature change in 2070 relative to 2010, under the IPCC RCP 4.5 and RCP 8.5 scenarios Note: both scenarios are from an ensemble of
five simulations with the GISS-E2R model.
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climate-modifying impacts described above. Care needs to be taken not to assume linearity in the impacts. In other words, relatively small changes in temperature, precipita-tion and their combinaprecipita-tion can result in organisms reaching threshold conditions that can lead to cascading effects.