Is global warming natural?

I was reading yet another anthropogenic global warming article
Better world: Find out if we can cool the planet [source]
and it occurred to me to check who is instead talking about the hypothesis that GW is natural.
And here they are ;)

Global Warming Natural, May End Within 20 Years [source]

Global warming? It's natural, say experts [source]

Global Warming: A Chilling Perspective ''During the last 100 years there have been two general cycles of warming and cooling recorded in the U.S. We are currently in the second warming cycle. Overall, U.S. temperatures show no significant warming trend over the last 100 years.''[source]

What if GW Were Natural? [source]

Is global warming a natural occurrence? [source]

Global Warming as a Natural Response to Cloud Changes Associated with the Pacific Decadal Oscillation (PDO) ''A simple climate model forced by satellite-observed changes in the Earth’s radiative budget associated with the Pacific Decadal Oscillation is shown to mimic the major features of global average temperature change during the 20th Century – including three-quarters of the warming trend. A mostly-natural source of global warming is also consistent with mounting observational evidence that the climate system is much less sensitive to carbon dioxide emissions than the IPCC’s climate models simulate.''[source]

Is global warming for real? ''Essenhigh's reasoning appealed largely to common sense: Carbon dioxide, the most widely discussed greenhouse gas, is part of earth's vast store of carbon (about 150 billion tons), which is continually being cycled through the oceans, the atmosphere, and vegetation. The human contribution to atmospheric carbon in the form of CO2 is small, less than 5 percent of the total carbon reservoir. Ergo, humans aren't causing global warming. I omit a lot of ancillary discussion, but that's the nub.'' [source]