Nice to see an academic realising that an over-leveraged economy cannot spend its way to prosperity.

Mainstream Keynesian economics is facing its last hurrah. The global fiscal stimulus championed last year by the Obama administration is coming undone, repudiated by the same Group of 20 that endorsed it last year. Now, against a backdrop of a widening sovereign debt crisis, we need to abandon short-term thinking in favour of the long-term investments needed for sustained recovery.

Keynesian stimulus was premised on four dubious propositions: that it was needed to prevent a global depression; that a short-run fiscal boost would jump-start the economy; that “shovel-ready projects” could combine short-term cyclical and long-term structural agendas; and, last, that the rapid rise of public debt occasioned by stimulus need not be a concern. That these ideas were so widely accepted was a testament to the perennial political attractiveness of tax cuts and spending increases.

In fact, the ubiquitous references last year to the Great Depression were glib; the policymakers had panicked. Adroit central banking could and would prevent depression. The hastily assembled stimulus packages were a throwback to naive Keynesianism. The relevant fact was that the US, UK, Ireland, Spain, Greece and others had over-borrowed for a decade, so a decline in consumption after 2007 was not an anomaly to be fought but an adjustment to be accepted.

Certain counter-cyclical spending is vital on social grounds. But stimulus measures such as temporary tax cuts for households or car scrappage schemes were dispiriting wastes of scarce time and money. They reflected a hope that a temporary fiscal bridge would carry us back to consumption and housing-led growth – a dubious proposition since the old “normal” had been financially unsustainable.

The talk of a green recovery, in which the fall in consumer spending would be offset by investments in sustainable energy, made sense and still does. Yet it was quickly undermined by the politicians’ insistence on “shovel-ready” projects. The shift to sustainable energy systems is a vital but long-term task. It could never be a short-term jobs programme. Maybe in China there are shovel-ready projects of sufficient scale, but not in the US.

Taking office in January 2009, President Barack Obama inherited the largest peacetime budget deficit in US history. By increasing it further, he made it his rather than his predecessor’s. He and his advisers ignored one of the key insights of modern macroeconomics: that the result of fiscal policy depends not only on current taxes and spending but also on their expected trajectories in the future.

The US was not in a credible position to raise an already enormous deficit “temporarily” because the prospect for future deficit cutting was and remains extremely clouded. America has absolutely no consensus on how to restore budget balance, as it is trapped between a federal government that provides too few public investments and services and a public that is almost maniacal in its opposition to tax rises. One cannot build a credible long-term fiscal policy by starting off in the wrong direction, with larger rather than smaller deficits.

The writer is director of The Earth Institute at Columbia University

Copyright The Financial Times Limited 2010.