Well theres a lot of things that can effect the climate and throughout recorded history there have been a series of deadly climate and geological events that have significantly impacted the human population... I see no mention of volcanic activity for example, the little ice age that killed of the medieval settlements of greenland or the great storms of the norths sea which swept away huge areas of land from the coast both in Britain and Europe...
This is not to say that human pollution has not had a serious effect and there is no doubt in my mind of that, but climate events over a number of years that come and go are a regular cycle for which we can only expect to see worse in the future as a result of humanitys contribution....
I'm sure there are lots of contributing factors, but yes I think the Novarupta eruption could have been a contributing factor being rather large at VEI 6 perhaps a kickstarter, the point is the article doesn't entertain such events..
Theres an extensive list of confirmed eruptions at https://volcano.si.edu/search_eruption.cfm most are relatively minor but it could be the quantity rather then quality that matters here...
An interesting article here on the subject https://earthdata.nasa.gov/learn/sensing-our-planet/volcanoes-and-climate-change
As all of us know, there are many interacting events that can affect weather. Certainly a major volcanic event is one. As for those of you who live in the western USA know, smoke from multiple major wildfires is another . . . could battlefield smoke been another? Sun spots activity is yet another. But there are many other annual events (eg, alignment of planets) that we're not generally aware of, but historical records show that the frequency can be shown to occur in sine waves with periods differing from short term to long term. When maximum (or minimum) values of multiple sine waves occur simultaneously, the weather can be affected adversely. Although I've never seen such a report, this could be the cause of bad weather during WW1. A certain, unnamed individual who is currently President of the United States seems to feel this way about global climate change. Sorry, but I don't know how to explain it more clearly, but as a career oceanographer I can attest that such events occur in the ocean, and the atmosphere mirrors the ocean.
Geology... I found these two article interesting I guess anyone whos read about the mine war will have read about the impervious blue clay under much of the region...
and one for Gallipolli which may be of interest, the article is free to read but you need to join and use the "read 100 articles a month free" for independent researchers option:
