Solving the ecological threat the planet faces, says Gates in a Tuesday blog post titled, “State of the Energy Transition,” will require the invention of clean technologies that replace the current ways we make things like steel and fertilizer. The cost of those technologies, he says, will have to be low enough that they can be utilized around the world—and deploying them must also be cost-competitive.

“Low- and middle-income countries are building aggressively to achieve the standard of living their people aspire to—and they should be,” he wrote. “Many countries in Europe and North America filled the atmosphere with carbon to achieve prosperity, and it is both unrealistic and unfair to expect everyone else to forgo a more comfortable life because that carbon turned out to change the climate.”

Gates notes that developing countries are responsible for two-thirds of total greenhouse gas emissions these days. China alone, he notes, is responsible for more than one-quarter of the emissions. But since first-world countries earned their wealth through burning fossil fuels, Gates argues it is their responsibility to lead development on the solution.

“Europe and the United States, which have historically produced the vast majority of CO2 emissions, owe it to the world not only to eliminate our own emissions but to invest aggressively,” he says. “This will give other countries that didn’t have much to do with causing climate change a chance to stop emitting greenhouse gases while growing their economies and raising their standard of living.”

While Gates says some governments and companies have shown an understanding of the urgent nature of the climate problem, he still believes the world is not moving at a fast enough pace. Clean technologies, which are designed to reduce annual greenhouse gas emissions from 51 billion tons to zero are not currently practical, cost-effective, or able to be deployed at scale.

And the way to avoid a climate crisis, he says, is to mobilize “the largest crisis response in human history”.

Part of the reason reducing greenhouse gas emissions is so hard, he says, is because virtually everything we make and do produces them. Electricity, which is often pointed to as a chief culprit, is only responsible for 26% of global emissions, he says. And transportation is only responsible for 16%.

Manufacturing is the biggest sector, with industries like those that make cement, plastic and steel causing 30% of emissions. And agriculture is in the top three, generating 21%.

“There are currently no cement plants in the world, and exactly one steel plant, that don’t produce CO2,” he says. “There are currently 2,412 coal-fired power plants in the world, and that number is still going up. Every single one of those plants will have to be replaced.”

Gates says his measure for success is Green Premiums, the cost difference between a clean technology and one that emits more greenhouse gasses. If businesses and governments can get those near, at or below zero by 2040 for a wide range of products and processes, he says, that will be a good long-term sign.

“This is the hardest challenge people have ever faced,” he says. “There has never been a mobilization of this scope, at this scale, at this speed, for this long. But humanity has also never faced an existential crisis like climate change. I am optimistic about what people are capable of in a crisis, and in the long run, I wouldn’t bet against us. Unfortunately, we don’t have the luxury of a long run.”