Interviewed for ITN/Channel 4 News, I was asked – very
reasonably – why anyone should listen to economists’ views on the economic
impacts of Brexit, when many short-term forecasts that a Brexit vote would lead
to a sharp slowing of the economy had been proved wrong. This was my response:
“Short-term economic forecasting is very unreliable. Just because the weatherman gets it wrong about whether it’s going to snow tomorrow doesn’t mean that the scientists have it wrong about whether climate change is going to make the planet warmer over the medium to long term”
I think it’s worth
explaining this. The forecasters –
including City economists and independent
research institutions like NIESR and IFS, as well as the Treasury and the
IMF - who predicted economic gloom as a direct result, not of Brexit itself but
of the referendum result, did so on the basis of the expected impact on
financial markets, business and consumer confidence: “Our
research shows that a vote to leave would increase uncertainty and, at best,
reduce growth”.
But they were (mostly)
wrong. On the markets, while the pound
did indeed fall much as expected (which is actually good for economic activity
in the short-term; the exchange rate acts a shock absorber to the expected long
term hit to the economy by making UK exports cheaper) market interest rates
didn’t rise and the stock market didn’t collapse (although UK companies have
certainly underperformed). More importantly, after an initial shock to
confidence, businesses and consumers appear to have decided that nothing has
happened yet and nothing much will happen for a while; so it’s business as
usual. Research on uncertainty, it turns out, isn’t exactly a certainty.
We can dismiss a
couple of excuses for this failure. It’s true Brexit hasn’t happened yet – but
the forecasts were explicitly related not to Brexit, but to the uncertainty and
expected future impact of Brexit. It’s true some (but not all) of the forecasts assumed immediate Article 50 notification,
but that was not central – and if it was uncertainty that was supposed
to drive economic weakness, delaying notification merely prolongs the
uncertainty. And it's true there was a policy response from the Bank of England - but if anything could have been forecasted it was that.
So what forecasters
fundamentally got wrong was their judgement about the short-term behaviour of
millions of individuals interacting in a very complex system, where (as we know
from the analysis of such systems) relatively small changes in a few variables
can lead to quite different outcomes. The
claim that “the flap of a butterfly’s wing in Brazil can set off a tornado in
Texas” is poetic
license – but the inherent difficulty of forecasting short to medium term
perturbations is true both of the economy and the weather.
Now, despite these
difficulties, weather forecasting has got considerably more reliable over the
last 20 years, so there’s plenty of room for economic forecasters to improve –
but explaining how the economy will do
in the next few months is always likely to be very challenging. That’s true of
economic forecasting in “normal” times: but it’s even more so the case when
trying to assess the short-term impacts of a political event on the
psychological attitudes of consumers and investors.
By contrast, predictions
about the long-term impact of Brexit – like climate science - are based on quite different reasoning,
about how changing one key factor – our openness to trade, or the degree to
which the earth’s atmosphere retains heat – changes the long-run properties of
the system. The methodologies used are
well-established and robust – and while of course the detailed modelling of
their impacts requires considerable expertise and huge amounts of data, the
basic mechanisms at work are well-established and easy enough to explain. The operation of the greenhouse effect can be
demonstrated in a school lab.
Similarly, the basic
insights of the “gravity model” approach to predicting international trade –
that trade between two economies depends on how big each is, how far apart they
are, and historical, cultural and policy factors including the existence of
special trade arrangements like the EU – are common sense, and their empirical
and practical validity is not seriously in question. More CO2 will make us hotter: less trade and
migration will make us poorer.
Now, economists’ forecasts
of the long-term impacts of Brexit could still be wrong – or inaccurate- just
as climate scientists could be wrong about the path of climate change. First,
our scenarios could be wrong; Brexit could turn out very differently from the
options (hard or soft, clean or chaotic) most people are trying to analyse;
similarly, sudden technological advances could change the path of CO2
emissions. Second, the numbers are
probably more uncertain even more than the models (which already incorporate some
forms of uncertainty) suggest – some forms of uncertainty are simply impossible
to model.
So while we can predict
that Brexit will reduce growth and CO2 will warm the planet, we should take the
quantitative modelling on just how large these effects are with a large pinch
of salt. In particular, feedback effects
could either amplify or dampen the impacts – and it is very difficult to guess
which. But the basic point - that reductions in trade and migration will reduce
growth and productivity, relative to what otherwise would have occurred – is
very unlikely to be disproved, any more than the greenhouse effect.
So how should that
translate into how we actually make decisions?
Well, I listen to the weather forecast: but, like most Londoners,
whatever it says, I always carry an umbrella.
On the other hand, that doesn’t mean I’d buy a house on a flood plain.
