I wonder, if some countries are secretly conducting geoengineering - would it be detectable? would there be any hint different from "anomalous heating" we observe now?
Basically every country has been conducting a massive geoengineering project in the open for the past decades by releasing billions of tonnes of CO2 (and other greenhouse gasses) into the atmosphere. We've been able to detect that, yes.
It really depends on what you mean by geoengineering. Dumping things into the atmosphere has been easy to detect for a while now, but with NASA spinning down their space assets focused on climate data [1] there’s definitely dimensional data that’s being lost. However, there’s still plenty of data being supplied via the EU Copernicus team [2] to track a lot of those things that hopefully will be able to fill some of the gaps.
All of this to say, with enough stable overhead assets then most things can be detected that would cause possible impacts in climate.
