The Maple Ridge Wind Farm in upstate New York in 2013. (Ron Antonelli/Bloomberg News)

In general, changes to our energy system come slowly. It’s a marathon, not a sprint.

In general.

Nonetheless, 2015 is shaping up to be a pretty special year and a pretty significant 365-day shift in how we get our power, says a 2015 power market outlook released Thursday by Bloomberg New Energy Finance.

“This Research Note is more sensationalist than we typically write,” it confesses.

The reason is a combination of three separate factors all moving in the same direction — an expected record for renewable energy installations, another forecast record for coal plant retirements and booming natural gas. The consequence, if these forecasts are realized, would be considerably cleaner energy and an impressive one-year drop in U.S. emissions.

“There’s basically these three big shifts underway, and they result in a drop in emissions, but more important, a structural shift towards a more decarbonized power fleet,” said William Nelson, BNEF’s head of North America analysis.

First, there’s the growth of renewables. BNEF is expecting a record of 18.5 gigawatts worth of renewable power sources to be built this year. That would exceed the prior record of 17.1 gigawatts in 2012.

Breaking that down, BNEF expects solar energy to set records in three separate areas — utility scale installations, rooftop installations and nonresidential rooftop builds. Wind will contribute roughly the same amount as solar to the record year for renewables, the report predicts.

That itself is noteworthy — wind currently accounts for a significantly bigger proportion of overall U.S. electricity generation than solar. But solar has seen exploding growth recently.

But that’s just the start. The spike in renewables will be accompanied, the report forecasts, by “the largest wave of coal retirements in US history.” Fully 7 percent of U.S. coal energy generation is expected to shut down, spurred in part by the onset of a key mercury emissions rule but also by a tougher overall economic picture. The upshot will be “a fundamental reduction in coal’s share of the US power mix,” the report says.

“This could be the year that goes down in history as the year when we retire the most coal ever,” Nelson said.

And then, there’s natural gas. The prior record for natural gas burn was 25 billion cubic feet per day in 2012, notes BNEF, but 2015 stands to tie or eclipse that, driven by low prices and much “switching” from coal to gas burning.

“When gas prices drop, gas generators are able to undercut the price of coal-fired electricity,” Nelson said. “So even for the coal plants that stick around, they’re being challenged on an hourly basis by cheap gas.”

Here’s a figure from the report, showing forecast trend lines for rising gas and declining coal burning as a part of the U.S. electricity mix:

The overall upshot of these changes, the report forecasts, should be a 2 percent drop in U.S. greenhouse gas emissions from 2014 to 2015 — and an overall emissions level from the electric power sector that is 16 percent below where the sector’s emissions were in 2005.

This, too, is significant, in that U.S. GDP is forecast to grow between 2.3 and 2.7 percent over the course of 2015. If power sector emissions fall while GDP rises, that would suggest a “decoupling” of economic growth and emissions growth, at least for that sector — an encouraging sign that economic improvement doesn’t have to have, as a downside, faster growing climate risks.

[Why the global economy is growing, but CO2 emissions aren’t]

So what does it all mean?

One year still is, well, one year. In the grand scheme, we still will be getting more power from coal than from natural gas in 2015, more power from natural gas than from nuclear, more power from nuclear than from renewables. Energy wonks will not see any change to that overarching story, which has been consistent for some time.

Still, the trends are clear, and particularly noteworthy in light of the ever-intensifying battle over the Environmental Protection Agency’s Clean Power Plan — the proposed greenhouse gas regulation that would allow states to choose how to cut their emissions by privileging natural gas, renewables and other less-carbon-intensive choices.

The unmistakable upshot of the policy is that the United States will be getting a lot more of its power from wind, solar and natural gas, and a lot less from coal, the most-carbon-intensive fossil fuel to burn.

But that plan isn’t implemented yet — indeed, the EPA has not yet released its final rule, which is expected this summer — and the rule’s “compliance period” wouldn’t begin until 2020. It’s a major regulation, and it appears to be the future — but what 2015 shows is that, with or without it, we’re moving that way anyway.

Clarification: This article previously stated that BNEF was forecasting that 2015 greenhouse gas emissions overall would be 16 percent below 2005 levels. Actually, the forecast is only for emissions from the electric power sector. The text has been changed to reflect this.