The Earth has been getting warmer -- but how much of that heat is due to greenhouse gas emissions and how much is due to natural causes?

A leaked report by a United Nations’ group dedicated to climate studies says that heat from the sun may play a larger role than previously thought.

“[Results] do suggest the possibility of a much larger impact of solar variations on the stratosphere than previously thought, and some studies have suggested that this may lead to significant regional impacts on climate,” reads a draft copy of a major, upcoming report from the U.N.’s Intergovernmental Panel on Climate Change (IPCC).

The man who leaked the report, StopGreenSuicide blogger Alec Rawls, told FoxNews.com that the U.N.’s statements on solar activity were his main motivation for leaking the document.

'The main premises and conclusions of the IPCC story line have been undercut by the IPCC itself.' — StopGreenSuicide blogger Alec Rawls

“The public needs to know now how the main premises and conclusions of the IPCC story line have been undercut by the IPCC itself,” Rawls wrote on his website in December, when he first leaked the report.

Rawls blames the U.N. for burying its point about the effect of the sun in Chapter 11 of the report.

“Even after the IPCC acknowledges extensive evidence for ... solar forcing beyond what they included in their models, they still make no attempt to account for this omission in their predictions. ... It's insane,” he told FoxNews.com.

Some skeptical climatologists say that the statement in the U.N. draft report is important, but not game-changing.

“The solar component is real but not of sufficient magnitude to have driven most of the warming of the late 20th century,” Pat Michaels, the former president of the American Association of State Climatologists, and current director of the Center for the Study of Science at the Cato Institute, told FoxNews.com.

The U.N. report also says that the effect of solar activity will be “much smaller than the warming expected from increases in [man-made] greenhouse gases.”

An estimate from NASA said that solar variations caused 25 percent of the 1.1 degree Fahrenheit warming that has been observed over the past century.

But Michaels said that if the U.N. increases its estimates about how much the sun affects Earth’s temperatures, it might help the U.N. get its prediction models back on track. While the Earth warmed over the last two decades, it did so more slowly than the U.N. had predicted.

“Climate science has the problem of trying to explain why we are now in our 17th year without a significant warming trend. As a result, you are seeing many forecasts of warming for this century being ratcheted down,” he said.

Others say that the focus on solar activity distracts from the big picture -- the fact that the Earth is warming.

“I see climate contrarians try this trick almost every time a big new solar study comes out. They somehow tend to neglect mentioning that solar variation is smaller than the heat-trapping power of carbon dioxide,” Aaron Huertas of the Union of Concerned Scientists told FoxNews.com.

To back that up, Huertas points to data that show that solar activity and temperature rose together from 1880 until 1960, but that then, solar activity stopped increasing -- even as temperatures continued going up.

“The basic evidence is that solar activity has varied a bit while global temperature keeps going up,” Huertas said.

But Rawls said that while solar activity has indeed stopped increasing, the important thing is that it remains at a historically high level.

“The simplest way to put it is: If you put a pot on the stove at the maximum temperature, and leave it on at that temperature -- are you telling me that the pot won’t keep warming?”

Rawls worries that if solar activity falls, the effects could be dire.

“Unlike warming, cooling really is dangerous, regularly dropping the planet into hundred-thousand-year-long glacial periods.”

NASA has said that there is evidence that the most recent “Little Ice Age” was caused by a dip in solar activity.

“Almost no sunspots were observed on the sun's surface during the period from 1650 to 1715. This extended absence of solar activity may have been partly responsible for the Little Ice Age in Europe,” during which temperatures were colder by about 1.8 degrees F than they are today, NASA has reported.

But Huertas said that’s not what we should worry about at a time when the effects of warming are already being felt.

“Climate change is affecting weather all across the planet and when it comes to extreme weather, the strongest links are to coastal flooding [and] heat waves,” Huertas said.

“While climate skeptics are arguing on the Internet about drafts of the report, states like New York and New Jersey are working to help people rebuild their homes in ways that have a better chance of surviving more destructive storms and flooding in the future,” he said.