Long climate simulations found that different release strategies can produce different effects on Atlantic ocean circulation, even when they meet the same temperature targets.
Researchers proposed a new 150-year simulation design to study stratospheric aerosol injection while separating its effects from other changing influences. Using the Community Earth System Model, they tested three injection strategies: two that managed global temperature and broader north–south temperature patterns, and one that managed global temperature alone.
The strategies produced different changes in the Atlantic Meridional Overturning Circulation, a large system of ocean currents. The researchers also modified an earlier experiment and found significant differences in the resulting climate response without changing the temperature targets.
Different climate outcomes
The researchers ran three 150-year simulations of stratospheric aerosol injection in a scenario designed to isolate the intervention's climate effects from transient changes other than carbon dioxide. Two simulations used a strategy with independent injections at 30 degrees north, 15 degrees north, 15 degrees south and 30 degrees south to manage global temperature and large-scale north–south temperature differences. A third used injections at 30 degrees north and 30 degrees south to manage global mean temperature only.
The two simulations using the first strategy had the same temperature targets but different injection patterns. The simulation that injected mostly at 15 degrees south slowed, but did not prevent, the decline of the Atlantic Meridional Overturning Circulation compared with the baseline. The simulation that injected mostly at 30 degrees north and 30 degrees south stopped the circulation's decline, as did the temperature-only strategy. The researchers say these results show that different long-term climate states can meet the same temperature targets. They also created an ARISE-hybrid ensemble by changing the injection strategy in an earlier experiment without changing its temperature targets, and found significant differences in the climate response.
Why the strategy matters
The findings show why temperature targets alone may not describe the broader effects of stratospheric aerosol injection. Two strategies can achieve the same target temperatures while producing different outcomes for a slowly changing part of the climate system, such as the Atlantic Meridional Overturning Circulation.
The results also indicate that short simulations may miss some long-term effects. Comparing alternative strategies over longer periods could therefore change how the consequences of stratospheric aerosol injection are assessed.
