"As somebody who's been writing about this subject for getting on twenty years now, it's astonishing how the climate has changed in the last five years"

Anthony Holden is referring to the changing attitudes towards a particular subject he has actually been blogging about for twenty years. He is amazed by the significant shift in opinion that has happened in the last five years. This could be due to a range of factors, such as new research study, technological advances, or a shift in popular opinion. It could also be due to a mix of all of these things. Whatever the cause, it is clear that the climate of opinion has changed considerably in a fairly short time period. This is something that Holden finds amazing, and it is a testament to the power of the media, technology, and popular opinion to shape the discourse around a particular topic.