Climate Characters: Meteorologist stopped doubting when he couldn’t disprove.

Editor's note: Climate Characters follows five people with varied views on climate change with the goal of bringing a greater degree of compassion and understanding to the highly polarized conversation.

Josh Kastman also changed his mind about climate change in an unexpected way. Now a mid-range forecaster at the National Oceanic and Atmospheric Administration's Weather Prediction Center, he had completed four years of meteorological training when he entered graduate school at the University of Missouri in 2011. Nevertheless, he still believed that natural cycles, rather than human activity, were the primary driver of present-day global warming.

“Growing up, it was easier for me to latch onto the climate denier side of the debate," he said. Kastman, a Christian Scientist who grew up in Springfield, Missouri, was subscribing to the ideology of his referent group: religious Midwesterners. But he wanted to know more.

Kastman completed his bachelor's and master's degrees in atmosphere science at the University of Missouri, then entered the Ph.D. program. When it came time to defend his dissertation, his beliefs about climate change were put to the test. One of his professors challenged him to “prove" human-induced climate change using his knowledge of meteorology, while another instructed him to “disprove" it. He quickly realized it was easy to fulfill the former request, but virtually impossible to fulfill the latter.

“As a scientist, you start off disbelieving until you see hard evidence. I went from someone who was on the fence to someone who really embraces the concept [of human-induced climate change]," Kastman said.

Though he's now convinced, along with the vast majority of climate scientists, Kastman concedes that the issue is a murky one. What he learned mostly was: it's complicated.

When energy from the sun enters the Earth's atmosphere, some is reflected back into space and some is absorbed by the planet as heat. Compounds in the atmosphere known as greenhouse gases increase the radiation that's trapped on Earth as heat, essentially acting as a blanket that warms the planet.

This isn't altogether a bad thing: without natural greenhouse warming, our planet would be an icehouse where life could not exist. The problems begin as human activities disrupt the balance by adding vast quantities of these gases in a very short time. But plenty of other factors shape climate.

Even among the people who agree that the globe is warming, the discussion turns to why. Is it mostly what humans are doing, or do natural cycles play a role?

People release lots of gases into the atmosphere, but different greenhouse gases behave in different ways. Whereas water molecules move through the water cycle in just seven days, carbon dioxide lingers in the atmosphere for 400 years. This means that a reduction in carbon emissions today may take decades or centuries to translate into global cooling.

Humans also repurpose land, turning wild or rural areas into cities, creating what's called the urban heat island effect. Whereas bare or vegetated land can cool itself off through evaporation, a slab of concrete has no such option. The result is that cities heat up faster than nearby rural areas: up to 22 degrees Fahrenheit overnight, according to the Environmental Protection Agency.

Natural cycles also play a role. Some parts of the planet reflect more light than others: the polar ice caps reflect more sunlight back into space than anything else on Earth. But as they continue to melt, they are replaced by dark ocean water, which absorbs radiation and amplifies warming. This is only one of multiple such “feedbacks" that make the climate response to man-made emissions so hard to predict.

"Extremists on both sides of the spectrum use half-truths in their arguments."-Josh Kastman

Volcanic eruptions can cause cooling in the short term by blocking incoming sunlight, and warming over longer periods by releasing greenhouse gases. Even the strength of solar radiation changes over time. On top of all this, scientists are unsure whether changes in cloud cover and type will result in more or less warming, as clouds act both as greenhouse “blankets" and solar reflectors. The point is, climate science is an extremely complex topic.

Science is complicated, and yet people constantly oversimplify it.

“Everything has become politicized by the right and the left to prove their points," Kastman says in an interview. “Extremists on both sides of the spectrum use half-truths in their arguments."

While some make honest errors in an effort to translate jargon into digestible tidbits, others intentionally manipulate facts to prove their point.

“It happens on the left too, with people you think would cherish the scientific data," Kastman says. For example, he says volcanic activity is repeatedly dismissed as wholly insignificant, when it's actually the third or fourth most powerful impact on the planet's temperature—there just happens to be a lull at the moment.

Repeated use of inaccurate language, often by the media, is a particularly problematic type of oversimplification. “The terminology they use changes, and the words are not always robust," Kastman says.

For example, consider the term “extreme." Reporters use the word to describe meteorology on a daily basis; two inches of rain is called “extreme," when, Kastman said, the term should be reserved for weather events that occur once a century.

“When something truly extreme does happen, how do you communicate that?" Kastman says. “That kind of watering down of the language has been hurtful." This gives credence to accusations of climate alarmism—often, hyperbolic language renders an otherwise valid message inaccurate.