10 Year Challenge: How the world has changed in a decade
If you've been pretty much anywhere on the internet in the last couple of weeks, you'll have no doubt come across #10YearChallenge on social media.
If not, the premise is simple - post a 2009 photo of yourself next to a recent one, to show how much you've changed.
Millions have taken part, but some have criticised it for being - among other things - narcissistic, ageist and sometimes a bit sexist.
But now people are using the hashtag to reflect on bigger changes. Such as...
In this tweet, footballer Mesut Ozil compares what appears to be a large iceberg on the left, and a melted iceberg on the right.
Although the meme isn't entirely accurate - the photo on the left, of the in Antarctica, was taken in November 2016 rather than in 2008 - there's no denying that shrinking ice sheets continue to be a major issue.
According to , Antarctica is losing about 127 gigatonnes of ice mass every year, while Greenland loses 286 gigatonnes annually.
This, they say, is largely down to rising global temperatures being absorbed by oceans. The planet's average surface temperature has risen by about 0.9C since the late 19th century - and about a third of that has happened in the last decade.
Environmental activist groups are also using the hashtag to highlight this issue.
This post from Greenpeace bends the challenge a bit, by comparing archival photos from 1928 with images taken by Swedish photographer Christian Aslund in 2002.