By William C. Shelton

(The opinions and views expressed in the commentaries of The Somerville News belong solely to the authors of those commentaries and do not reflect the views or opinions of The Somerville News, its staff or publishers.)

“Global warming is the second-largest hoax ever played on the American people, after the separation of church state.”

That’s James Imhofe, Chairman of the U.S. Senate Committee on Environment and Public Works when Republicans controlled that body. He likened the environmental movement to the Third Reich. He said that the Environmental Protection Agency resembles the Gestapo, and its administrator Carol Browner, Tokyo Rose.

He represents the portion of climate-change deniers whose ideology is impervious to evidence. For them, science is the work of the devil.

The first five months of this year saw the most Tornados for that period in U.S. history. There were 875 in April alone, resulting in 7,525 deaths.

In ten states, it has been the wettest March and April in history, breaking 1,300 precipitation records across the Midwest and South. Record-setting crests along the Mississippi flooded 6.8 million acres and caused $3-to-4 billion in insurance losses.

Meanwhile, extreme drought has ravaged Texas, southeast Arizona, New Mexico, and along the Gulf Coast to the Florida panhandle. Dead pastures and dead livestock have cost Texas farmers $2 billion. Wildfires have burned 2 million acres and are still burning.

No single weather event or cluster of events is evidence of climate change. But put enough of them together over a long enough time, and they make an historical trend.

Climate change skeptics cite certain scientists when they deny the trend’s existence. These scientists are often medical researchers, zoologists, physicists, engineers, and only rarely, climatologists.

Two independent studies surveyed hundreds of scientists who are engaged directly in climate research. Both studies found that 97% believe that global warming is happening, and that it is caused by human activity. A survey of all 928 peer-reviewed research papers on the subject published between 1993 and 2003 found not a single one that rejected that hypothesis.

A majority of nonscientists who are skeptical about climate change are not ideologues. Indeed, skepticism is essential to good science. And scientific fact is not just a show of scientists’ hands.

John Cook of the organization Skeptical Science has compiled the best available evidence that comprehensively examines the global-warming hypothesis from multiple lines of inquiry. The consensus of the evidence is the same as the consensus of the scientists: the structure of our atmosphere is changing, and the change is caused by us.

There is little disagreement that carbon dioxide (CO₂) traps heat. The debate is whether global warming is happening over the long term—not just periods of a few years—whether it is caused by increased atmospheric carbon caused by humans burning fossil fuels.

Global warming is happening

At least eight independent studies have used a multitude of data and analytic techniques to reconstruct historic global temperatures. Since the late 19^th Century, average temperatures have continually risen beyond anything seen over the previous 1,800-year study period.

Independent examinations of data recorded by a variety of satellites over the last 40 years find a continuing and accelerating reduction in heat escaping into space. As greenhouse gases have trapped heat in the lower atmosphere, the upper atmosphere has become cooler, as measured by these satellites and weather balloons.

Temperatures of the world’s oceans have steadily increased over 40 years as well. Only a global-warming hypothesis can explain this particular pattern of increases. Oceanic surface-temperature warming increases the number and severity of hurricanes.

Other evidence of global warming that emerges from exhaustive studies are that sea levels are rising, Spring is coming earlier, species are migrating toward the poles and higher altitudes, tree lines are doing the same, global humidity is increasing, and glaciers, snow covers, the polar cap, sea ice, and ice sheets are all melting.

Fossil fuel burning is elevating CO₂ levels

The fact that atmospheric CO₂ levels have increased from about 318 parts per million in 1960 to 390 today is a simple matter of measurement. The fact that today’s level is higher than at any time over the last 800,000 years is a matter of examining the fossil record. But are humans causing it?

Some skeptics will acknowledge global temperature increases, but deny that they result from atmospheric CO₂ increases. The satellite evidence mentioned above finds the infrared radiation reductions at the exact wavelengths where greenhouse gases absorb energy.

During the day, the sun warms the earth’s surface. At night, heat radiates into space. If increased solar energy were causing global warming, daytime temperatures would be increasing faster than nighttime temperatures. Instead, warmer nights have been increasing faster than warmer days since 1977.

Fossil fuel burning releases the isotope Carbon 13. Plants release the lighter isotope Carbon 12. The proportion of Carbon 13 in the atmosphere, coral, and sea sponges has been increasing since 1860.

Ignoring this and similar evidence, propagandists say that human-made CO₂ is tiny in comparison to what nature pumps out. Indeed, every year plants breathe out 444 billion tons of CO_2, and oceans outgas 332 billion tons of CO₂, while humans produce 23 billion tons.

But plants also breathe in CO₂ to grow, and oceans absorb it as well. Together, they absorb 788 billion tons, about 12 billion more tons than they produce. This reduces human-made CO₂ by about half. The remaining 13 billion human-made tons accumulate, accounting for the increases in atmospheric CO₂ described earlier.

I have heard climate change skeptics make the bizarre claim that farting Chinese cows produce more greenhouse gases than fossil fuel burning.

It’s true that cow farts are mostly methane, which is a greenhouse gas nine times more potent than CO_2. And it is true that beef consumption has become a status symbol in rapidly developing economies like China. But there are more belching tailpipes and smokestacks in the world than farting cows.

Readers who would like references for the scholarly studies that support the points made here may request them when this column is posted to our website.