revise SST climate forecasts: `mean(sst_sd)` annual, monthly (observed) vs annual (forecast)

[bbest]

• [ ] 1. fix standard deviation calculation: https://github.com/noaa-onms/climate-dashboard/blob/79ab5430d177421e78bd251e8c9909ab0c73db57/scripts/process_nc.R#L35-L37
• [ ] 2. get ranges to match with similar time steps for comparison; since not matching with switch from monthly (observed) and annual (forecast)
• [ ] 3. consider different temporal extents, eg since 1970 (not 1850), and either limit available data or zoom to this extent by default.

[bbest]

from Mitch Roffer:

• Error bars on graphs
• Error propagation in climate models | The Hump of the Camel

[bbest]

Frank: expect to see more uncertainty into future, ie expanding cone