In the fight against climate change, trees are an ally. They suck in carbon dioxide, reducing the harmful greenhouses gases in our air. But there’s a problem — we’re asking them to work overtime.

Trees can’t absorb enough of the carbon dioxide humanity is throwing at them, unless we turn every inch of available land into a dense forest, according to Christophe Jospe, the chief strategist at Arizona State’s Center for Negative Carbon Emissions.

But what if trees — or machines modeled after them — had superpowers? Artificial trees with otherworldly abilities are a great hope against climate change, as environmental experts say it’s not realistic to expect humanity to release significantly less carbon into the atmosphere. Our best bet may be to capture the excess carbon and store it or convert it into something useful such as fuel.

Five years ago, a Boston group recruited two designers to develop artificial city trees. The trees they envisioned offered shade and would absorb carbon dioxide. The thinking was to place the trees where soil was too shallow to host traditional trees.

The group delivered beautiful mock-ups, but so far little else has come from it. Finding funding is a challenge.

“You don’t want to be the first person to pay,” said Kimberly Poliquin, the director of SHIFTBoston. “Scientists have figures, but you don’t know if that’s going to be the reality once you built it.”

Capturing and storing carbon isn’t yet the type of expense that local governments and organizations can slide into their budgets. The cost of the technology is dropping, but not to a point where it’s affordable to install “forests” of these systems. Poliquin estimates an upfront cost of $350,000 for an artificial tree, but she expects prices to come down considerably. She hopes to develop a prototype of such a tree in one or two years.

There’s plenty of interest in removing carbon from air. One method is to capture carbon directly from the smoke stacks of power plants. Another method — which the Boston project targeted — is pulling carbon out of open air, where it isn’t present in as much density. In theory, one square kilometer of artificial trees could remove 4 million tons of carbon a year, according to the Center for Negative Carbon Emissions, which is developing a technology to work in open spaces.

Seven large-scale projects to capture and store carbon at power plants will arrive in 2016 and 2017. Most are in the United States and Canada.

But much more growth is needed before carbon capture and storage makes an impact on climate change. According to the Global Carbon Capture and Storage Institute, the 15 large-scale projects operating around the world can capture 28 million tons of carbon dioxide per year. To keep climate change in check, we’ll need to process 4 billion tons in 2040 and 6 billion in 2050.

The Center for Negative Carbon Emissions is developing technology that it says is 1,000 times as effective as trees, per unit of biomass. The group is located in the desert because their technology responds well to warm, dry air and requires less energy in that environment. Operating in cooler climates such as Boston would add expenses.

Once the technology is fully built out, they expect to remove a ton of carbon dioxide for about $100 a ton. Their long-term estimate is less than $30 per ton. As is, there’s no resemblance to a tree as scientists including those at Arizona State focus on making the carbon removal process effective and affordable rather than beautiful to look at.

More developments are needed for it to be cost-effective and spread around the world. According to the Global CCS Institute, since 2007 the global investment in carbon capture and storage has been less than $20 billion, about one-hundredth of the investment into renewable technologies.

“It needs the likes of Mike Bloomberg, Bill Gates, Mark Zuckerberg and Tom Steyer to champion early technology efforts to bring the cost down,” Jospe said. “Find me $100 million and I’ll tell you how to put it to a very aggressive research and development agenda, and five years later you can see some exciting technologies that start to show on the market.”

Gates is one of the investors in Carbon Engineering, a Calgary company developing industrial-grade technology to capture carbon and make fuels. It’s a promising case, but not yet something ready to substitute in for a tree in a city park.