Changes in atmospheric composition have been the main drivers of climate change in the 20th century, and will remain important in the future. Whilst CO2 is the dominant driver, changes in methane (CH4), ozone (O3) and aerosols are also significant, but are much less well understood. These species are much shorter-lived than CO2, because they are chemically reactive, with atmospheric lifetimes ranging from about a decade for CH4 down to days for ozone and aerosols. These timescales are similar to many transport and mixing rates in the atmosphere - this means that distributions of these species are controlled by a combination of transport, mixing and photochemistry. Their relatively short lifetimes mean that control measures that target these species may offer opportunities to significantly influence climate change over the next few decades (e.g., Penner et al., 2010). We use a variety of models to simulate these non-CO2 species, at both global and regional scales.
One research focus is on modelling tropospheric ozone, including its contribution to radiative forcing of climate change (e.g., Stevenson et al., 2006). New radiative forcing calculations for both tropospheric and stratospheric ozone over the time period 1850-2100, based on the ozone fields used in CMIP5 simulations are shown above. The future time period shows projections for tropospheric ozone for four different emission scenarios; stratospheric ozone has only been evaluated for a single scenario.
Investigators: David Stevenson