Like other countries the United States is also supposed to say next year how much it will cut emissions by 2035 as part of the 2015 Paris climate agreement. Harris could afford to set an ambitious target of, say, a reduction of 65%,  versus 2005 levels, because there’s sufficient time for investments that lower carbon emissions to pay off. But that would require decisive action soon after taking office.

One question is what tools a Harris administration might use to hit both the existing 2030 target and a new 2035 one, says Adair Turner, chair of the UK-based Energy Transitions Commission. There are three main options: more subsidies along the lines of the IRA; tighter regulations on carbon emissions from power stations, petrol-powered vehicles and other big polluters; and taxing emitters by putting a price on carbon.

Subsidies are inefficient and costly at a time when the U.S. government is struggling to rein in its budget deficit. Many economists prefer taxing carbon because it is the most efficient way of curbing emissions and raises cash. However, it could push up the cost of living.

Harris advocated carbon pricing when seeking the Democratic nomination in 2019, while promising to shield households from the expense by giving them back a dividend from the proceeds. But it’s hard to see a big push in this direction unless the Democrats win a majority in Congress. Regulation might therefore end up carrying much of the burden of curbing emissions.

One thing Harris almost certainly will not do is curb U.S. production of oil and gas, which has reached record levels during Biden’s presidency. The vice president reversed her previous view that the government should ban fracking on federal land and last week said she will not change her current position.

But those who want to phase out fossil fuels should not be too worried. After all, much of the increased U.S. oil and gas production has gone to European countries, which needed an alternative to Russian hydrocarbons after Moscow invaded Ukraine. More important is that the United States curbs consumption.

FINANCE AND TRADE

What a possible Harris administration does abroad may be as vital as what it does at home, says Peter Hill, who ran the United Nations’ climate conference in Glasgow in 2021. This is because emerging and developing countries such as India, which contributed little to carbon pollution in the past, are still ramping up their emissions, he writes in a forthcoming paper.

Helping these countries green their economies rapidly will reduce global warming. But there are other reasons for the United States to provide support. First, if Washington doesn’t provide a competitive offer, it will lose out to China which is also wooing countries in the Global South. Second, the more developing countries suffer from climate change, the more their citizens will try to migrate to richer and cooler countries, such as the United States.

The Group of Seven large industrial countries already has a plan to help developing countries decarbonise their economies, which I helped craft. Harris has been enthusiastic about this scheme, according to a White House official. She also understands the importance of investing in poorer countries as part of her work on tackling the root causes of migration from Central America, the official said.

If Harris wanted to supercharge these initiatives, she would have several options, especially if she can persuade Congress to provide some cash. One would be to roll out what Brian Deese, one of her advisers, last month called a “clean energy Marshall Plan”. This would subsidise developing countries to buy U.S.-made green technology.

Another option is to scale up the World Bank and other multilateral development banks so they can fund the green transition. The Biden administration has been pushing these institutions to squeeze more out of their existing balance sheets and mobilise private sector capital. Harris could build on this work by recapitalising these banks.

But climate finance should be only one element of a strategy to engage with the Global South. The other is trade. The Biden administration has advocated “friendshoring” – a plan to build up supply chains in allied countries to avoid excessive dependency on China. But its policies, including the IRA, have at times built American industrial strength at the expense of other countries, including its friends.

A key question for a Harris presidency would be how much it is willing to work with allies on a global green industrial policy. And those countries’ willingness to reciprocate will depend on how much the next U.S. administration curbs emissions at home.

All these ideas are up in the air until the November election. But one thing is certain. The planet is frying and ambitious climate leadership from a Harris presidency is one of the best hopes to limit the damage.

(The author is a Reuters Breakingviews columnist. The opinions expressed are his own.)