The UKESM1 ARISE experiment explores the impacts of geoengineering via the injection of sulphur dioxide (SO2) into the stratosphere. The injections occur at four different latitudes: 15 degrees N & S and 30 degrees N & S, at an altitude of approximately 20 km.

The simulations are based on the medium-emissions CMIP6 scenario ssp245 and cover the years 2035 to 2070. They form a 5-member ensemble with initial conditions taken from the corresponding five members of the ssp245 simulations upon which they were based.

There are three targets for the ARISE simulations:

1. Annual, global-mean near-surface air temperature to be cooled down to, and then maintained at, 1.5 degC above the pre-industrial mean (the latter determined from the long-term mean of UKESM1's CMIP6 piControl simulation).
2. The hemispheric temperature balance to be returned to and maintained at the same level as when the global-mean temperature was 1.5 degC above pre-industrial.
3. Same as target (2) but for the average poles-tropics temperature difference.

Using a 5-member ensemble mean, a period in UKESM1's CMIP6 historical/ssp245 simulations was identified when the 20-year mean global temperature was 1.5 degC above pre-industrial. The temperature pattern during this period (2014-2033) was used to define targets (2) and (3) above.

The amount of SO2 injected at each location is adjusted annually by an algorithm which examines the temperature distribution in the previous year, compares it with the three targets descibed above, and adjusts the injection rate for the next year accordingly