Despite a large body of scientific evidence linking global warming to human activities, only one-out-of-three U.S. voters (34%) believe humans are to blame for climate change. Forty-eight percent (48%) of likely voters attribute climate change to long-term planetary trends.

These numbers reflect a reversal from a year ago when 47% blamed human activity while 34% said long-term planetary trends according to a new national survey by Rasmussen Reports.

Most Democrats (51%) still say humans are to blame for global warming, the position taken by former Vice President Al Gore and other climate change activists. But 66% of Republicans and 47% of adults not affiliated with either party disagree.

However, sixty-two percent of all Americans believe global warming is a serious problem, with 33% who say it’s Very Serious. Thirty-five percent (35%) say it’s a not a serious problem. The overall numbers have remained largely the same for several months, but the number who say Very Serious has gone down.  

Even though U.S. President Barack Obama has made global warming a priority for his administration, only half (49%) of Americans think the president believes climate change is caused primarily by human activity. This is the first time that belief has fallen below 50% since the president took office. Just 19% say Obama attributes global warming to long-term planetary trends.  

Roughly half (48%) of U.S. voters believe the president is doing a good or excellent job on energy issues, almost two-thirds (63%) say finding new sources of energy is more important that reducing the amount of energy Americans currently consume.  

A growing number of Americans (58%) say the United States needs to build more nuclear plants, an increase of five points from last month and the highest finding so far this year. Roughly 40% believe there is a conflict between economic growth and environmental protection

The results are from a national survey of 1,000 likely voters, conducted 15-16 April 2009.

The Rasmussen survey results seem to parallel a recent analysis by U. S. climate scientists who say It’s wrong to blame our warming climate on human pollution alone, and that North America’s warming and drying trend is also due to important natural causes.

Natural shifts in ocean currents have caused much of the warming in recent decades, and almost all of the droughts, says the U. S. National Oceanic and Atmospheric Administration (NOAA). Some of the changes in North America’s warming trend of the past half-century have been due to shifting ocean currents, the NOAA team found.

It estimates the “natural” climate change is substantial and could account for close to half of all warming in North America, though it is still less than the amount caused by greenhouse gases.