Worldwide carbon-dioxide emissions rose to yet another record high last year — some 34.5 billion tons from fossil fuels and cement production.

But there was a small bit of good news for those worried about unchecked global warming. The pace of emissions growth now appears to be slowing.

That's the conclusion of a big new report from the PBL Netherlands Environmental Assessment Agency, which conducts an annual inventory of the carbon-dioxide emissions that are heating the planet. (The report excludes emissions from deforestation as well as other greenhouse gases such as methane.)

In 2012, the report estimates, global carbon-dioxide emissions rose 1.1 percent. That's a clear increase, but it was also a considerably smaller increase than the 2.9 percent average growth over the previous decade.

What's more, the slowdown in emissions growth wasn't due to weak economic conditions — global GDP actually grew 3.5 percent in 2012. Usually the two grow in lockstep. This report hints that world's economic growth may be "decoupling" from its carbon use, the report argues, "which points to a shift towards less fossil-fuel intensive activities, more use of renewable energy and increased energy saving." For now, however, the evidence for that is mostly suggestive.

Reasons for slower growth

Why the slowdown? Mainly because of some shifts among the world's biggest economies:

-- U.S. carbon-dioxide emissions dropped nearly 4 percent in 2012 as natural gas edged out coal and vehicles became more fuel-efficient. (As we've noted, that trend already seems to be reversing in 2013.)

-- European Union emissions dropped 1.3 percent due to a decrease in energy consumption and a 4 percent decline in road freight transport. Much of that drop was driven by the weak euro zone economy.

-- China's emissions "only" rose 3 percent — which was well below the 10 percent growth the country averaged in the previous decade. The end of the nation's stimulus programs caused a drop in electricity demand. Likewise, hydropower generation surged by 23 percent, as China recovered from the 2011 drought and added new capacity. And, at the margins, there were improvements in energy-efficiency.

-- As for the other major emitters: Carbon emissions in Russia dropped 0.9 percent, but they rose by 7 percent in India and 6.2 percent in Japan. (Japan saw a big jump in emissions after shutting down its nuclear power plants post-Fukushima.)

Note that it's difficult to disentangle the short-term blips from the long-term trends. For instance, the big surge in Chinese hydropower isn't going to get repeated every year. And coal seems to have halted its slide in the United States, at least for now.

Will global emissions ever decline?

And, of course, global carbon emissions still haven't dropped, a necessary condition if the world wants to meet its goal of avoiding 2°C in global warming. For that to happen, the report notes, a few big things would need to occur, such as:

-- China would have to achieve its goals of reducing energy consumption by 2015 and shift from coal to natural gas, with gas supplying 10 percent of the country's energy needs by 2020.

-- The United States would have to continue its shift away from coal and toward natural gas and renewable energy.

-- The European Union would have to repair its emissions-trading system and keep cutting carbon emissions. (Right now, the report notes, there are signs that coal was making a comeback.)

Developing nations are increasingly important

The report also noted that the world was about to hit a milestone: Developing nations will soon account for half of all the carbon-dioxide that humans have put in the atmosphere. At the moment, those countries are responsible for 48 percent of cumulative emissions between 1850 and 2010.

That matters because, as the study notes, "discussions at the U.N. climate negotiations tend to focus on which countries have contributed most to climate change." Here's a chart showing the breakdown:

A few other interesting bits:

-- The amount of non-hydro renewable power — solar, wind, and biofuels — doubled between 2006 and 2012 and is now supplying 2.4 percent of the world's energy needs. That may not sound like much, but the pace of growth has been increasing. That said, global fossil-fuel consumption continues to grow as well.

-- The concentration of carbon-dioxide in the atmosphere rose at an unusually high rate — by 2.2 parts per million in 2012 — even though actual emissions slowed. The report notes that this was likely due to "variation in net carbon storage of forests and absorption by the oceans."

-- Note that the report excludes carbon emissions from "deforestation and logging, forest and peat fires, from post-burn decay of remaining above-ground biomass, and from decomposition of organic carbon in drained peat soils." Including these could increase wiorldwide emissions by between 10 percent to 20 percent or more. "However," the report notes, "these percentages are highly uncertain and show a large annual variability."