Visit by former director of the Royal Dutch Meteorological Institute

For our master course Urban Resilience in a Changing Climate, we were visited by Gerard van Steenhoven, former director KNMI, and I had the chance to learn something new. 

We've all seen it, the graph form the IPCC on the observed global mean surface temperature change. What I didn't get yet is what does 'climate' mean if we look at 30 years of average weather, when we have both measurements since about 1880 and we also know there's been an impact due to our emissions since 1850. What is then this 'average weather'? It is generally considered to be the climate at the beginning of this period, though until around 1980 it is also considered to be 'not that bad'.

This raises another question though. In this graph we see a rise in the global mean surface temperature around 1930, though this trend stabalizes around 1960, before rising again from 1980 onward. Why? Why is this not a rising line from 1930? And the answer is nuclear testing (and bombing), and the consequent particles emitted into the air that blocked incoming radiation. If we forget about all the negative consequences and why these tests were stopped in the first place, we might almost see it as beneficial to create a nuclear winter to decrease the global mean surface temperature.