As you point out, there are several valid reasons to subsidise farming. But then subsidise farming, not carbon emissions! And while you are at it, use those subsidies to encourage farming that is sustainable, both for the climate as well as biodiversity.
And that can be sustained in international crisis: farming that is a house of cards highly dependent on international supply chains of fertilizer, feedstock and fuel won't help you all that much under blockade.
No-one mentions this when food security is discussed. The farmers here in NL use the security excuse too but absolutely no-one mentions that their food production is directly dependant upon the import of magnitudes higher tonnage of feedstock - soya from Brazil - than the meat / dairy it produces. Then I'm not even looking at the fertilizers / chemicals which are also imported.
Isn't that what they are doing? They subsidize the farmers separately, and charge a carbon tax separately. Even if those are initially the same amount you would think that the incentive structure would encourage farmers to shift to less c02 methods, as that improves profit?
What's the point of a carbon tax if it's balanced by a government subsidy?
Edit: Genuinely curious what I'm missing..
Low carbon farms balance would be: "low carbon" profit + subsidy - small carbon tax
High carbon farms balance would be: "high carbon" profit + subsidy - high carbon tax
If ["low carbon" profit - small carbon tax] > ["high carbon" profit - high carbon tax] (e.g. if the carbon tax is high enough), farms have an incentive to lower their carbon emissions.
The subsidy is here to make sure ["low carbon" profit + subsidy - small carbon tax] > 0
The subsidy could be independent from the carbon emissions (e.g. by subsidies on the produced goods) while the carbon tax isn't, effectively creating an incentive to produce in a less carbon intensive manner.
If I can make 1 unit of food for €50 and use 50 tons of carbon, or make it for €60 and use 10 tons of carbon, a carbon tax and food subsidy would allow me to sell that €60 low carbon food for €50 and force me to sell the high carbon food for €60
This gives an economic incentive to use the lower carbon method, funded by those who use more carbon, while not changing the end price or output.
Just to provide the numbers: in 2030, a tax will be introduced of 120 DKK (~16€) / ton CO2e, which linearly increases each year until it reaches 300 DKK (~40€) / ton CO2e in 2035. However, the farmers can get subsidies for changing their practices and adopting new technologies, in order to reduce their emissions. I.e., the government will give you money to change your production, so you can minimize the carbon taxes you have to pay. There are more technicalities to how it works, but that's the gist of it. The important part is that the goal is to transition to new technologies and production methods, which reduces emissions per unit food produced.
There will be no food subsidy, however, and a rough estimate of the increase of food cost is something like 1.5%, with beef having the highest increase. Take this estimate with a grain of salt though, as it's difficult to estimate. An increase in food cost is expected though.
You tax the carbon (something you want less of) and you subsidise something else you want more of. So you might end up with the average farmer not having a change of costs, but still disincentivising stuff we don't want e.g. carbon emissions.