How are CO2 emission effects and high altitude effects of air travel compared to each other? The climate impact of air travel is often divided into CO2 emissions and "high altitude effects" like that of water vapour and cloud formation. The effect of the emitted CO2 is cummulative, as CO2 has a high retention time in the atmosphere. On the other hand, as I have understood it, the high altitude effects are more short lived. Their impact on temperature are determed by current levels of air travel, and not past.

How can the size of these two effects be compared to each other or to other sectors such as travel by car? Is there any videly accepted method for this? It seems a bit like apples and oranges to me.

I know about GWP, that uses a somewhat arbitrary timeframe of 100 years. Is and can that be used here? I have also heard about RFI, but I am unsure how that works or is applied to this.
The CO2 is a greenhouse gas which causes a net heating effect as it retains additional solar radiation, the exact magnitude of this effect is still highly debated. The high altitude effects you've mentioned are often referred to as "jet exhaust shading" and it's estimated, based on some temperature data from the week after the 9/11 attacks in the US, that it causes roughly 4°C of cooling, this is because the jet exhaust contains water which condenses out as high albedo clouds, and sulfur compounds that absorb solar radiation as well as the CO2.