First the good news: In a new report on the near term future of the global renewable energy industry, the International Energy Agency is projecting impressive growth. Renewable sources like wind, solar, and hydropower should constitute nearly two-thirds of new net power capacity brought online across the globe between now and 2020. That’s equivalent to 700 gigawatts of new capacity or “more than twice Japan’s current installed power capacity,” according to the IEA.

That would mean that overall, renewables would grow from providing 22 percent of the world’s total electricity generation in 2013, to providing an impressive 26 percent of it by 2020.

But then, well, there’s the bad news. According to the IEA’s new Renewable Energy Medium-Term Market Report, the rate of renewables growth, which has been explosive of late, is actually set to “level off.” It’s hardly opportune time for that to be happening, with the world about to assemble in Paris to try to tackle climate change.

“This flattening of the annual new installations means that renewable electricity is off track from the pattern that we would need to meet ambitious climate change mitigation goals,” says Paolo Frankl, who heads the IEA’s renewable energy division and oversaw the report.

The core problem, says IEA, is a bevy of policy uncertainties and other renewables integration problems in various countries — what you might collectively call the sector’s growing pains. In the U.S. alone, such growth-thwarting uncertainties include the unclear fate of several tax incentives, the expectation of extensive battles over the implementation of the Clean Power Plan, and state-level fights over how individual homeowners will be credited on their bills for solar energy they generate and feed back to the grid.

Still, renewable electricity growth will be considerable. Strikingly, two-thirds of the new renewable deployments are expected to occur in developing countries like Brazil, India, and China. The latter will be responsible for a staggering 40 percent of all of the world’s growth in renewable electricity capacity by 2020, says the IEA, “an amount triple the current total power capacity of the United Kingdom.”

Of the top sources of new renewable energy deployments, onshore wind is expected to lead the way — accounting for more than a third of the total — followed closely by solar photovoltaics. New hydropower installations are expected to account for a fifth of the total, and to be particularly prevalent in developing countries.

For Sub-Saharan Africa, the report verifies that the phenomenon dubbed “leapfrogging” — in which some countries will pass over fossil fuel based electricity and go straight to renewables — appears to be a reality. “With huge resources, improving economics and policy momentum, renewables should meet almost two-thirds of power demand growth in [Sub-Saharan Africa] through 2020,” it finds.

Yet the IEA report is very critical of lingering policy gaps and other hurdles that are interfering with growth, such as those in the U.S. Financing hurdles are also an issue. Consider, Frankl suggests, the same solar photovoltaic installation but in one case located in Dubai and in another case located in central Africa. “The interest rates will be so much higher that the same PV electricity, the costs would double,” Frankl says.

Overall, if both developing and developed countries solved some of the problems that bar the investment in, and the integration of, renewable sources, then IEA suggests that the growth of renewable electricity could be 25 percent greater from here out to 2020.

Indeed, the IEA’s Frankl notes that with its recent announcements in conjunction with the U.S., China has actually taken a step in this direction. The country has just announced a “green dispatch” plan that will mean “giving priority, in distribution and dispatching, to renewable power generation and fossil fuel power generation of higher efficiency and lower emission levels.” This should help put China — and thereby, the world — on a much more ambitious path.

“Whatever they do better, the world will do better,” says Frankl. “They are really 1 order of magnitude higher than anyone else.”

All in all, then, the IEA’s new findings reaffirm that we are moving more and more into a world powered by wind, water, and sun. But at the same time, they also provide still more evidence that the world is not moving fast enough — either in its planned emissions cuts, or in its renewable energy deployments — to keep global warming within a reasonable range.