Most Read: Local

Posted at 01:45 PM ET, 11/09/2010

Do Americans think global warming is manmade?

* Sun and 60: Full Forecast | Von Karman vortex streets *

Andrew Freedman, in yesterday's piece Scientists launch climate science counter attacks, wrote "a majority of Americans already accept manmade climate change as a reality."

Capital Weather Gang's Matt Rogers challenged Freedman with the following comment:

Andrew, what is your source for this statement: "a majority of Americans already accept manmade climate change as a reality"? The Yale poll you linked in a previous article said 50% and a recent Rasmussen poll is running at 39%.

Then reader marcusmarcus cited a New York Times op/ed by Stanford researcher Jon Krosnick who stated his polling indicates "...huge majorities of Americans still believe the earth has been gradually warming as the result of human activity."

But as Matt Rogers then pointed out, a closer read of the polling data might lead one to a more nuanced conclusion. It indicates 45% of Americans think natural causes and human activities contribute to global warming equally, 30% believe it's mostly human and 25% mostly natural. Also, 24 percent of respondents - in a separate question - indicated they didn't think the Earth was even warming.

Other polls out there offer varying results:

* The latest poll I could find, released by Pew Research on October 27, indicates just 34% of respondents replied there is "solid evidence" the Earth is warming due to human activities compared to 18% who stated the warming is due to natural causes. Thirty-two percent responded the Earth isn't warming.

* A survey from Angus-Reid, published October 21, found 42% of Americans think "global warming is a fact and is mostly caused by emissions from vehicles and industrial facilities."

* A Gallup poll from March shows 50% of Americans attribute warming more to human activity than natural causes.

The variability in these results likely reflects the different way the poll questions and responses were designed.

Notice the different questions and response options among the various polls I've mentioned:

* From Rasmussen: "Is Global Warming caused primarily by human activity or by long term planetary trends?" Potential problems: There is no option for a roughly equal mix of causes. Also, the question forces those who don't believe warming is happening to pick a cause, which is odd.

* From Yale: "Assuming global warming is happening, do you think it is...Caused mostly by human activities, Caused by both human activities and natural changes, Caused mostly by natural changes in the environment, None of the above because global warming isn't happening, Other, Don't know." Potential problems: The option of both human and natural causes had to be volunteered by respondents and was not provided as stated option, likely biasing that option's result on the low side (just six percent). Also, only seven percent chose "none of the above because global warming isn't happening" whereas as in separate question 19% of respondents said global warming wasn't happening, and 19% said they didn't know if it was happening.

* From Stanford (Krosnick): "[Assuming global warming is happening] Do you think a rise in the world's temperature is being (would be) caused mostly by things people do, mostly by natural causes, or about equally by things people do and by natural causes?" Potential problem: This wording forces people who don't believe warming is happening to attribute a cause. Twenty-four percent of respondents in a previous question indicated they thought warming had probably not occurred over the last 100 years.

* From Pew Research: "Is there solid evidence the Earth is warming? Yes, [and if yes], Because of human activity, Because of natural patterns [or] Don't know; No; or Don't Know." Potential problem: The poll doesn't allow respondents to say it's a mix.

* From Angus-Reid: "Which of the following statements comes closest to your view of global warming (or climate change)? Global warming is a fact and is mostly caused by emissions from vehicles and industrial facilities, Global warming is a fact and is mostly caused by natural changes, Global warming is a theory that has not yet been proven, and Not sure." Potential problem: The option of a mix of natural and human activities is absent.

* From Gallup: "And from what you have read or heard, do you believe increases in the Earth's temperature over the last century are due more to the effects of pollution from human activities or natural changes in the environment that are not due to human activities?" Potential problems: This question doesn't allow respondents to indicate it's a combination. Also, you could argue that Gallup's use of the word "pollution" might bias results because the notion of global warming gases being "pollutants" might be controversial to some respondents.

Clearly, one can find shortcomings with the design of all of these questions and response options. Considering all of the results together, what seems to be evident is that of Americans who believe the globe is actually warming, about half believe it is mostly manmade - per the Yale and Gallup polls. But, as about 20-30 percent of Americans don't believe warming is happening at all (depending on the survey), it seems well less than half - probably between 35 and 40 percent per the Pew Research and Angus-Reid poll - believe warming is both occurring and mostly manmade.

Because few polls explicitly provide an option for a partial contribution of human activities to the observed warming, it's difficult to say whether Freedman's statement "a majority of Americans already accept manmade climate change as a reality" is supportable. That appears to be a gray area that better polling design might help clarify- which excludes those who don't believe warming is happening from voting on the cause and allows those that do believe warming is happening to indicate it might be a result of a combination of factors (rather than mostly/all natural or mostly/all manmade).

So here's a challenge for readers: How would you design a poll question to more accurately gauge public opinion about global warming and its causes?

By  |  01:45 PM ET, 11/09/2010

Categories:  Climate Change

Read what others are saying

    © 2011 The Washington Post Company