On the August 4 edition of MSNBC's Tucker, host Tucker Carlson claimed "[t]he world is getting warmer," but we don't know “why” because "[t]here's no consensus on that." Carlson's comments came in response to a caller who stated that, two days before, Carlson had incorrectly asserted that “nobody knows what [global warming] is.” In fact, as Media Matters for America has documented, organizations representing thousands of scientists share the consensus view that “human activities are responsible for much of the recent warming” of the planet, according to a June 2006 National Academies of Science report:

• Media Matters noted the June 22 National Academy of Sciences (NAS) report affirmed the “scientific consensus regarding human-induced global warming,” based on multiple “lines of evidence” supporting “the conclusion that human activities are responsible for much of the recent warming” of the Earth's atmosphere.
• Media Matters noted the Intergovernmental Panel on Climate Change (IPCC) found natural phenomena cannot account for the dramatic increase in global temperatures over the past half-century. According to the IPCC's third assessment report, which reviewed a wide array of scientific work in 2001, “Simulations of the response to natural forcings alone (i.e., the response to variability in solar irradiance and volcanic eruptions) do not explain the warming in the second half of the 20th century.” Citing multiple studies that demonstrated this “evidence for an anthropogenic [human-caused] signal in the climate record of the last 35 to 50 years,” the IPCC stated, “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.”
• Media Matters noted a 2001 NAS report found that greenhouse gases released by human activities are “causing surface air temperatures and subsurface ocean temperatures to rise.” Media Matters also noted the report takes into account both human contributions to greenhouse gases and natural occurrences such as glacial cycles, volcanic activity, and solar irradiance cycles.
• Media Matters noted the American Geophysical Union stated in December 2003 that "[h]uman activities are increasingly altering the Earth's climate. These effects add to natural influences that have been present over Earth's history. Scientific evidence strongly indicates that natural influences cannot explain the rapid increase in global near-surface temperatures observed during the second half of the 20th century."
• Media Matters noted a February 2003 American Meteorological Society report that stated: “Human activities have become a major source of environmental change. Of great urgency are the climate consequences of the increasing atmospheric abundance of greenhouse gases and other trace constituents resulting primarily from energy use, agriculture, and land clearing. These radiatively active gases and trace constituents interact strongly with the Earth's energy balance, resulting in the prospect of significant global warming. When used in this context, the term 'global warming' includes all climate and environment effects arising from natural climate variability as well as from anthropogenic [human-caused] changes in atmospheric composition and land use.”
• Media Matters noted the Pew Center on Global Climate Change website stated: “The scientific community has reached a strong consensus regarding the science of global climate change. The world is undoubtedly warming. This warming is largely the result of emissions of carbon dioxide and other greenhouse gases from human activities.”

From the August 2 edition of MSNBC's Tucker:

CALLER: Dave from L.A. It finally got a little cooler here, but man, this heat wave -- total product of global warming. And for some reason, global warming doesn't get the attention in the news that it deserves.

CARLSON: You've got to be kidding. Everybody talks about global warming all the time. What gets less attention is what global warming is. If you were to ask the average person, the average television [unintelligible], “What is global warming? Explain it in three sentences.” Not possible. Nobody knows what it is, but everyone's upset about it. Is this a result of global warming? I don't know. I'm not sure anyone does.

From the August 4 edition of MSNBC's Tucker:

CALLER: Wendell Whitmore from Los Angeles, California. You said no one understands global warming. Thousands and thousands of people understand global warming, and surely anyone that's seen An Inconvenient Truth understands global warming perfectly well. You, in fact, should see An Inconvenient Truth.

CARLSON: Oh, Wendell, you've seen Al Gore's movie? Oh, so you're an expert? You're basically a climatologist. You're a research scientist on the subject. The world is getting warmer. We know that. Do we know why? No, we don't. There's no consensus on that. And that's just a fact. Sorry Gore's movie didn't admit that, but it's true.