A number of people, including the occasional economic journalist, are puzzled about why government debt at 90% of GDP seemed to cause our new Chancellor and the markets so little concern when his predecessor saw it as a portent of impending doom. I always argued that this aspect of austerity had a sell by date, so let me try to explain what is going on.
The 90% figure comes from a piece of empirical work which has been thoroughly examined, and found to be highly problematic. (Others have used rather more emphatic language.) Part of the problem is a lack of basic thinking. Why should the markets worry about buying government debt, beyond the normal assessment of relative returns. The answer is that they worry about not getting their money back because the government defaults.
If a government cannot create the currency that it borrows in, then the risk of default is very real. Typically a large amount of debt will periodically be rolled over (new debt sold to replace debt that is due to be paid back). If that debt cannot be rolled over, then the government will probably be forced to default. Knowing that, potential lenders will worry that other potential lenders will not lend, allowing self fulfilling beliefs to cause default even if the public finances are pretty sound.
The situation is completely different for governments that can create the currency that the debt they sell is denominated in. They will never be forced to default, because they can always pay back debt due with created money. That in turn means that lenders do not need to worry about forced defaults, or what other lenders may think, so this kind of self fulfilling default will not happen.
Of course a government can still choose to default. It may do so if the political costs of raising taxes or cutting spending is greater than the cost of defaulting. But for advanced economies there is an easier option if the burden of the public finances gets too much, which is to start monetising debt. That is what Japan may end up doing, and what others may also do if QE turns out to be permanent. But this is a very different type of concern than the threat of default. And it does not, in the current environment, lead to the emergence of large default premiums and market panics.
How can I be so sure? Because with QE we have had actual money creation, and it has not worried the markets at all. It seems hard to tell a story where markets panic today about the possibility of monetisation in the future, but are quite sanguine about actual monetisation today.
So for economies that issue debt in currency they can create, there is no obvious upper limit anywhere near to current debt/GDP ratios when economies are depressed and inflation is low. Japan shows us that, and we must stop treating Japan as some special case that has no lessons for the rest of us. (How often did we hear of their lost decade in the 1990s that it couldn’t happen anywhere else.)
It was good that the IFS suggested Hammond has a look at Labour’s fiscal rule. As I explained in this post, Hammond’s new ‘rule’ is pretty worthless. But one key part of Labour’s rule that keeps being ignored but is crucial in today's environment is the knockout if interest rates hit their zero lower bound. It is for the reasons described above that this knockout is there and is perfectly safe: when interest rate policy fails you can completely and safely forget the deficit and debt and use fiscal policy to ensure the recovery. It is the basic macro lesson of the last 6 years that is fairly well understood among academic economists but still remains to be learnt by most people who talk about these things. Whether senior economists in the UK Treasury need to learn it or just keep quiet about it for other reasons I do not know.