It's important to also note, as explained in the article:
>"Grinnell was witnessing the glacier react to a relatively natural change in the climate. The Little Ice Age, which was a cold period when the park’s current glaciers were at their largest, ended in the late 1800s as the climate started warming. The melting of the park’s glaciers in the late 1800s, was a mostly natural reaction to the end of the Little Ice Age."
The quote, without context, implied to me that he had an understanding of anthropogenic climate change a century ago. While there were people[1] at that time who did theorize this was happening, I don't think that's what Grinnell was implying in his diary.
It's also the case that the amount of melting then pales in comparison to the amount occurring today - so I'm not attempting to say that what we see today may be the continuing of a natural climate fluctuation.
1. https://en.wikipedia.org/wiki/Nils_Gustaf_Ekholm