Its more than the 2040 agreement. Ordering diesel trains looks very bad in terms of climate change, especially given the complaints about HS2.
The best solution is simple, electrify.
Could they get away with lengthening some 195s, so technically they haven't brought extra DMUs even though in reality they have.
Extending the 2 car 195s to 4 car would mean they could be used in the many many places where 2x2 car units are used, especially around Manchester where this seems to be the formation of choice on many lines.
Talking about Northern's fleet and how many types they've got in use. Despite the 150s being old, replacing them isn't going to be an easy task considering how many of them there are, so maybe they should look at it from a different view point...
Are 153s still supposed to be leaving, if they are maybe 155s should go as well.
Secondly maybe introducing 170s into the mix was a bad idea, despite how modern the units are. Maybe a swap with 158s from Scotrail or EMR would be better.
Therefore Northern would be left with just 150, 156, 158 & 195s in diesel terms, and no 'micro fleets' as there are substantial numbers of all of them