I'd like to reclaim climate change from the list of touchy topics, including religion and politics, that we avoid bringing up with strangers.

Views on climate have become a marker of identity, like those other subjects. ADN's survey on Alaskan climate change attitudes, which I saw in an advance copy, shows that how you feel about climate science depends on your party, gender and age.

Older Republican men tend to say humans have no role in changing the climate. Younger, non-partisan women say we do.

This is strange, because whether humans are changing the climate isn't a matter of faith, like religion, or a matter of values, like politics. It is a matter of fact in the physical world. One side has to be right and the other wrong, regardless of how strongly either feels.

At this point, I've already lost readers who think it is impossible to bridge this divide. But if you hope for common ground, please read on. The basic science is surprisingly easy to understand. We can argue about a lot of related issues, but agreeing on core facts would help everyone.

As I go, I will label information that is known beyond dispute and information that could be open to interpretation.

In 1895, Svante Arrhenius, a Swedish scientist and Nobel chemistry prize winner, presented the first paper explaining how excess carbon dioxide in the atmosphere could warm the Earth. Carbon dioxide lets the sun's energy pass through on the way down to the ground, but when heat bounces up from the surface, carbon dioxide catches some of it, like a greenhouse window.

The way carbon dioxide absorbs heat is a fact that no one can argue about. Carbon dioxide detectors work on this principle.

In 1960, astronomer Carl Sagan used Arrhenius' insight in his doctoral dissertation on Venus. He predicted that the carbon dioxide in its atmosphere would make the planet unbearably hot. He convinced NASA to send its first successful planetary probe there, Mariner 2, in 1962. It confirmed that Venus' carbon dioxide atmosphere warms the planet's surface to 864 degrees.

But is the small amount of carbon dioxide in Earth's atmosphere enough to warm our planet? Arrhenius thought so, but his calculations were too rough to address complexities in the atmosphere.

In 1963, however, Syukuro Manabe, working in a government lab at Princeton, created a system of equations that could model the atmosphere in a primitive computer, and that even explained for the first time how some of its layers work. Three years later, he refined the model and introduced calculations to show how excess carbon dioxide would warm the atmosphere.

The results from that work, 50 years ago, have proved remarkably accurate as carbon dioxide has increased in the atmosphere. Another model Manabe built in 1975 took the predictions further, including showing that the world would warm faster in the Arctic, just as we have seen.

But could Manabe's calculations have left something out that will keep the Earth from warming more? Possibly. We can't disprove what isn't known. But with many billions of dollars of research over 50 years, no one has found anything. Despite vastly expanded knowledge and computers, Manabe's predictions have not been improved upon.

Could it be a coincidence that rising temperatures have tracked human carbon dioxide emissions and Manabe was just lucky?

Doubters point out that the climate has changed many times in the past through the cycle of ice ages. That's true. But we can look at those changes to see if they confirm or refute Manabe's calculations. Air bubbles in ancient ice, drilled out of glaciers in Antarctica, show exactly how much carbon dioxide was in the atmosphere eons ago.

Going back 800,000 years, temperature and carbon dioxide match up, as the models say they would. Carbon dioxide in the atmosphere increased when temperature rose, and when it decreased, temperatures fell.

Over the 800,000 years, carbon dioxide in the atmosphere varied between 170 and 300 parts per million—enough to produce the differences between ice ages and warm periods. Human emissions, mostly from burning fossil fuels, have now raised carbon dioxide to about 400 parts per million. Temperatures also have risen. 2015 was the hottest year ever measured, beating a record set in 2014.

Could the current rise in the carbon dioxide be coming from something other than human fuels?

Not possible. Government statistics report how much carbon dioxide is coming from our cars and factories. In fact, graphs of carbon dioxide in the atmosphere flatten when the world has an economic recession, because the carbon dioxide doesn't rise as fast then.

Could there be a conspiracy to lie about these numbers?

Some people say the Apollo missions never landed on the Moon. I've been to the National Air and Space Museum and the Johnson Space Center to see the spacecraft, and I remember seeing Neil Armstrong on a black-and-white TV in the basement of our house in Turnagain. But I've never been to the Moon, so I can't absolutely rule out a hoax.

However, ocean acidification is an aspect of carbon dioxide pollution that can be measured any day, anywhere in the seas of the world. The oceans are becoming less base (or more acidic) as they absorb excess carbon dioxide from the atmosphere. This is a physical fact that people can check.

More acidic oceans tend to weaken shells and destroy corals. Alaska biologists are already seeing impacts.

I'm also convinced climate change isn't a hoax because I've had the privilege to meet many of the scientists doing the work.

I met Syukuro Manabe 15 years ago when I was writing a book. He is a delightful and energetic man and spent all the time I needed to explain his work. At the time, he thought we already knew more than we needed to about how carbon dioxide warms the Earth — he didn't want more money spent on that kind of research.

Later, I also met Ken Caldeira, who discovered and named ocean acidification. Caldeira said that when he goes to Washington to explain the science, he is treated like another special interest group.

He said, "The special interest I represent is reality."

Charles Wohlforth's column appears three times weekly. His book about climate change is "The Whale and the Supercomputer." Email him: cwohlforth@alaskadispatch.com
