Tier II: Aerosol hemispheric asymmetry fingerprint

## Description
Evaluate the observable imprint of aerosol forcing via the NH–SH temperature asymmetry.

## Specification
- Interhemispheric temperature contrast (NH − SH mean surface temperature) trend over **1950–1985**
- Models should reproduce observed NH cooling tendency (or reduced warming relative to SH)
- Correct sign of associated tropical precipitation shift
- Compare against HadCRUT and Berkeley Earth
- Scored using CRPS framework

## Required variables
`tas`, `pr`

## Required simulations
historical

## References
Protocol §Tier II — Aerosol hemispheric asymmetry