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As a political conservative, Barry Bickmore didn't want to believe warming of the planet is caused by humans and is a problem requiring government intervention.

But after reviewing the science that supports climate-change skepticism, the Brigham Young University geology professor said, he realized he "had been badly misled" by political leaders bent on thwarting policies aimed at reducing carbon dioxide emissions.

"Much of what I saw was unbelievably sloppy, leaving out whole packages of data that would undermine their conclusions," Bickmore told reporters gathered Wednesday.

HEAL Utah hosted the press event to bring attention to the emerging impacts of climate change and to call on the state to pursue climate-friendly energy policies. Headlining Wednesday's event was Michael Mann, a leading climate scientist who heads the Earth System Science Center at Pennsylvania State University.

"Climate change is hurting us now in the United States whether you are talking about food, water, human health. It could be one of the greatest national security threats we face in coming years," said Mann, who is best known for a "hockey stick" graphic that shows a dramatic uptick in global temperatures in recent decades. "We are past the point where we can continue with a fake debate we have in our politics on whether climate change exists."

Opponents, including Rep. Jason Chaffetz, R-Utah, argue the science is unsettled as to whether carbon dioxide emissions are the cause of climate change, and caution that policies targeting emissions may hurt the economy without providing a significant environmental benefit.

Joining Mann and Bickmore in front of Salt Lake City's historic City Hall were University of Utah atmospheric scientist Court Strong and two city officials, water resources manager Laura Briefer and sustainability program director Debbie Lyons.

During the past century, humans have unearthed masses of carbon that nature spent 100 million years storing underground and injected it into the atmosphere in the form of heat-trapping carbon dioxide, released when fossil fuels burn. According to several reports released this year, the consequences are already being felt across the nation and the world and they will only magnify if emissions are not curbed.

The National Climate Assessment released this month, for example, reports that the American Southwest is seeing its stream flows diminish.

"Climate changes pose challenges for an already parched region that is expected to get hotter and, in its southern half, significantly drier. Increased heat and changes to rain and snowpack will send ripple effects throughout the region's critical agriculture sector, affecting the lives and economies of 56 million people — a population that is expected to increase 68 percent by 2050, to 94 million," the report states.

Some fossil energy groups, conservative think tanks and Republican senators have assailed the report as "alarmist," according to The Associated Press.

Drought and bark beetles, whose infestations are abetted by balmier winters, are killing forests and setting the stage for increased wildfire. And warming temperatures mean more of the state's precipitation would fall as rain, shrinking mountain snowpacks. This means runoff exits the mountains earlier and water supplies are exhausted when we need them most, according to Briefer.

Models indicate that Wasatch stream flows that supply residential use in Salt Lake City will shrink by 3.8 percent for every one-degree rise in average temperatures, she said.

Lyons described the city's various initiatives to reduce carbon emissions, such as phasing out two-stroke engines, equipping the city's fleet with vehicles that run on compressed natural gas, and increasing residents' transportation options to reduce reliance on cars.

"The risks of business as usual are enormous. We can't afford that," Bickmore said. "We have to establish policy decisions on sound science."

Salt Lake City Mayor Ralph Becker was among a national network of local officials who announced a report Wednesday calling for more help for communities preparing for the impacts of climate change.

"While the environmental consequences of a changing climate may vary by geography, we are unified in recognizing the critical role of the federal government to support cities building resilient communities," Becker, first vice president of the National League of Cities, said in a statement.

The report was delivered to a presidential task force examining climate preparedness.

Twitter: #brianmaffly