We could go a long way toward saving the world with a trillion dollars.

And while a trillion — which is one thousand billion — seems like a crazy fantasy level of money, it isn’t all that much in the grand scheme of things. A trillion dollars represents about 1% of the world’s GDP, an amount that one man — Amazon’s Jeff Bezos — will likely be worth one day soon.

In his new book “How to Save the World for Just a Trillion Dollars: The Ten Biggest Problems We Can Actually Fix” (The Experiment), out now, author Rowan Hooper lays out a plan to start writing checks in order to solve the planet’s biggest problems.

“If you spent the money very wisely, you could genuinely change the world,” Hooper, a senior editor at New Scientist, told The Post.

The book tackles 10 problems, from climate change to illness to poverty, and offers suggestions and a ballpark cost for solving them.

“It’s just getting it all to line up and getting everyone to sign on the line and spend it. That’s the real sticking point,” he says.

Here are eight of the more fascinating line items that, together, would add up to just over 1 trillion — A K A a Bezos and a half. It’s a steal!

Whiten the clouds: $1 billion
The world’s biggest polluters probably aren’t going to do enough to curb CO2 emissions in time to stop global warming. So scientists have been looking for other ways to cool the planet. In the 1990s, a climatologist named John Latham became obsessed with the Twomey effect, which expresses the amount of solar radiation reflected back into space from clouds. The denser the clouds, the more sunlight that bounces back. 

Latham realized that the cloud density could be increased by seeding them with tiny salt-water droplets. The theory has never been tested, but Hooper says “many are quite confident it would work, as it shows from sophisticated modeling.” Localized trials could be run, over the Great Barrier Reef or the Arctic, for example.

Stephen Salter, an engineer at the University of Edinburgh, has created a proposal for a fleet of autonomous hydrofoil ships that would pump an ultra-fine seawater mist into the clouds. 

Salter told the BBC that 300 of these ships could reduce global temperatures by 1.5 C.

“It wouldn’t cost very much to do a big-scale trial,” Hooper says. “It’s really important that someone finds the money to fund this thing.”

Farm insects: $10 billion
Some 30 to 40% of all the food produced is wasted, and that rotting refuse is responsible for about 8% of greenhouse gases. One solution is to feed the waste to insect larvae, such as the black soldier fly, which Hooper writes will “eat pretty much anything, growing into fat little maggots that can be dried and used as food.” The protein-rich bugs could be fed to livestock and farmed fish, or ground and added to bread or ice cream for us humans, for example. “People are squeamish and I think we need to put out programs to get people over it,” Hooper says. “People in the West used to be squeamish about sushi.” The insect farming industry is still relatively small, and scaling it up will require major investment and solving challenges such as how to grow meatier bugs faster. 

Incentivize building electric vehicles: $5 billion
Aviation accounts for 2.5% of global emissions, but cutting that down is going to take work. An electric car is doable. But an electric plane? It’s more difficult in part because we currently can’t fly very far on battery power. NASA and others are developing electric aircraft that can carry a handful of people — between two and six — and Hooper says green-powered jumbo jets will “take a little while.” One possibility is to power them with alternative fuels, such as hydrogen. In 2020, for example, a company called ZeroAvia flew the first commercial-size aircraft on hydrogen.

Hydrogen fuel is considered clean and produces only water as a byproduct — though currently the hydrogen is often extracted from natural gas, adding to pollution. More research is required to make it viable as an everyday fuel source. Offering incentives for all kinds of electric vehicles will help “speed the transition” to greener transportation, the author writes. 

Eradicate mosquitoes: $100 billion
Some 627,000 people — most young children — died from malaria in 2020, according to the World Health Organization. Scientists have tried for years to wipe out the vicious killer, mostly by using insecticide on the mosquitoes that carry it. But the disease always bounces back. One radical solution is to eradicate mosquitoes altogether using genetic modification to render the insects sterile. “A study looking at the effect of getting rid of mosquitoes found that removal is unlikely to have a big impact on the local ecosystem,” Hooper writes. 

Some small, in-lab trials have shown that this genetic alteration might be effective in curbing tropical diseases, but more research dollars are needed to study its viability in the real world. 

Buy up biodiverse land: $500 billion
The idea is simple: Take a huge wad of cash and start buying areas that are particularly important to biodiversity, such as forests in the Amazon. “There are more than two million square miles around the world that could simply be set aside, protected from grazing or development, and allowed to regrow,” the author writes. (Though acquiring that land would be pricey.) The plan would not only help restore and protect the plant and animal species in those areas, but it would have the added benefit of helping to capture more CO2 from the air naturally. “You’re tackling two crises in one go,” Hooper says. “And those are the two biggest problems by far, so that would be the most effective use of the money.”

Just give it away: $600 billion

Want to seriously dent global poverty? Hooper recommends handing each of the world’s poorest a check for $1,315 — a life-changing amount for the 760 million in sub-Saharan Africa, India and elsewhere who earn $2 or less per day. “What surprised me about that is that there has been a ton of research about what happens if you give a cash handout to people,” Hooper says. “They wouldn’t just blow the money and go and get drunk. Studies show people use it carefully.” They often buy an asset — livestock, for example — which they can build on to move up a few rungs on the poverty ladder and move out of the most dire circumstances. In one study in Sri Lanka, men were given a one-time cash donation. “Five years later, the men’s income had increased by 64% to 96% of the grant amount,” Hooper writes. “You could probably affect a gigantic change in people’s lives,” he says.

Create a green recipe competition: $10 million

No one’s going to eat more sustainably if it doesn’t taste good. So Hooper borrows an idea from ecologist David Tilman to run an annual cooking contest with 20 hefty prizes of $50,000 each for dishes that meet health and environmental guidelines. 

A panel of judges would taste the food and score it on a point system, evaluating its impact on water use, greenhouse gases and so on. The winners might be featured at a global restaurant chain. 

“I tried to fill up the book with things that we could genuinely implement that would get us to better place — things we could do without having this fantasy figure of a trillion dollars,” the author says. 

Identify every species: $10 billion

“We have no real idea how many species we share the planet with,” Hooper writes. We’ve cataloged more than 2 million, but one estimate suggests that might only account for 20% of living things. “This [cataloging] is vital because we’re in the midst of a terrible extinction crisis, and we have to find out what we’ve got before it disappears,” Hooper says. “Then we can make better plans to protect what’s out there.” Ecosystems are literally our life support, and if too many species disappear, the systems will start to break down. In spite of this bleak state of affairs, Hooper remains hopeful for the future of human beings. 

“The whole point of the book is to show that there are solutions out there,” he says.