For the past 30 years, the global approach to climate policy has been making grand promises and later mostly failing to live up to them. At his World Leaders Climate Summit, President Biden promised to cut about twice as much carbon as what Obama promised, which was hailed as decisive and bold climate action.

This is equivalent to decreasing an additional 1.5 billion tonnes of greenhouse gas annually by 2030 beyond Obama's commitments. But what would this achieve? Let us assume that Biden and future presidents manage to get emissions cut as promised by 2030. And let us assume miraculously that the many future presidents from 2030 to 2100 manage to continue that feat.

If we use the standard UN climate model, it turns out that Biden's new promises will reduce warming by the end of the century by a rather small 0.07°F — from say 7.2°F to 7.13°F. Biden told us that his climate policy would make Americans more prosperous. That is implausible. If climate policies really were making us richer, everyone would scramble to shed fossil fuels and pile on the renewables. Instead, his own summit showed the need for arm-twisting even just to make a few of the participants promise expensive new policies.

Achieving the promised cuts in less than a decade will force utilities to buy a lot of new and often more expensive renewables. They will have to buy much more back-up for when the sun isn't shining and the wind isn't blowing. Studies show that by 2030, 80 percent of the population would still prefer non-electric cars, but politicians will force everyone to buy only electric. Weatherizing houses, as Biden has proposed to cut emissions, can cost many trillions.

The President's own price sticker is $2 trillion on climate policy over his first term. This is equivalent to spending $1,500 per American every year on climate, while one survey shows that most Americans are unwilling to spend even $24. That is not politically viable long term.

However, the real story from the climate summit isn't Biden's 0.07°F reduction, but China, India and other developing nations' unwillingness to promise new carbon cuts, because they are more focused on development and getting their populations out of poverty. These countries matter, because they will make up three-quarters of this century's emissions, and they cannot spare trillions for climate policy.

In place of another gabfest, we need to get smarter on climate. It is not about the rich world spending trillions it doesn't have on ineffective and premature renewables. Leaders should instead spend billions smarter on green innovation: if we can innovate future green energy to be cheaper than fossil fuels, everyone will switch. To Biden's credit, this is one of his many climate promises, but it needs to be front and center of a successful climate agenda.

Bjorn Lomborg is president of the Copenhagen Consensus and a visiting fellow at the Hoover Institution. His latest book is "False Alarm: How Climate Change Panic Costs Us Trillions, Hurts the Poor and Fails to Fix the Planet."