First, if it's just from climate change, it will be gradual increase in scarcity and all kinds of methods of growing food become viable as the price of bread increases. So unless climate change actually makes Banksy undesirable, it will still be worth more loaves of bread than one person could eat in a lifetime.
Second, if it's an acute wide-spread disaster, the only thing that becomes relevant is food/water/shelter /weapons/first-aid. Not only would a Banksy be worthless, but so would the world's biggest diamond as well as the cure for cancer.
So it's a meaningless comparison just based on the fact that you don't like rich people out-bidding each other over art (and subsequently supporting artists).
Once you start down the road of being dictator of spending on expensive things that aren't solving starvation, all kinds of things like space exploration, the development of the internet, etc all become "sorry effects". Guess how many villages could be fed on the budget of the Apollo program.