An iceberg near Disko Island, Greenland, in 2011. (Brennan Linsley/Associated Press)

In his April 24 op-ed, “The scientific silencers take aim,” George F. Will claimed that debatable questions still include the extent to which humans are contributing to climate change. William Collins, director of climate and ecosystem sciences at Lawrence Berkeley National Laboratory, has succinctly made the case that humans are responsible. He states that the current astronomical and geological factors, such as changes in the sun, changes in Earth’s orbit and volcanic activity, simply can’t explain the increase in temperature in the lower atmosphere while the upper atmosphere is cooling.

Mr. Collins also explains that carbon isotopes come in different “flavors.” (Plants like the lighter isotopes of carbon.) Each mixture of carbon isotopes has a signature that can be measured and traced to its source. In the lower atmosphere, the carbon isotopes that are rapidly accumulating and trapping heat have been measured and can come from only one source: burning of fossil fuels. Case closed.

Michael Dominick, Arlington

“Climate change” is simply shorthand for a whole range of its concomitants, including environmental degradation, deforestation, desertification, atmospheric carbon dioxide and methane buildup, soil erosion and nutrient loss, toxic waste accumulation, sea-level rise, fossil fuel and other resource overuse, shortages of fresh water, fishery and coral reef decline, biodiversity shrinkage and increasing sociopolitical instability and violence. (What is fueling all of this? Human population, which has tripled since World War II.)

The U.S. government’s 1974 National Security Study Memorandum 200, adopted in 1975 by President Gerald Ford (R), discussed much of this and recommended universal access to contraception and abortion. The NSSM 200, however, was mysteriously classified and buried for nearly 20 years and then ignored.

Edd Doerr, Silver Spring

George F. Will relied on a 15-year-old National Academy of Sciences report to challenge the need for meaningful action to address the realities of climate change. Scientific knowledge relating to climate change has increased considerably since 2001. The National Academy of Sciences and the United Kingdom’s Royal Society concluded in 2014, “Scientists know that recent climate change is largely caused by human activities.”

Ironically, the April 24 news article “As ice melts, polar bears forced to swim for days on end” reported that the polar bear population in the waters off northern Alaska has dropped between 25 and 50 percent from 2001 to 2010 as the loss of sea ice continues its accelerating decline. Melting sea ice in the northern and southern polar regions is the direct consequence of atmospheric warming. Distinguished oceanographer Don Walsh assessed this effect of climate change on the world’s oceans in a recent issue of the U.S. Naval Institute’s Proceedings magazine. “Change is a reality,” he wrote, “and it is observable.”

The world’s population is projected to grow from today’s roughly 7 billion to 9 billion by 2050. It is irresponsible in the extreme to fail to address the continued fouling of our environment with unchecked carbon emissions. Just ask a polar bear.

Gordon I. Peterson, Springfield

I would like to make a deal with George F. Will: I will not presume that conservative thinking is inherently racist when some conservative makes a racist remark if he will stop presuming that progressive thinking is inherently against the First Amendment when some progressive proposes some nonsense to restrict freedom of speech.

Jim Parker, North Potomac

I was both outraged and amused by Sam Kazman and Ken Lassman’s petulant rant in their April 23 op-ed, “Attacking free speech on climate change,” regarding how the deep-pocketed, fossil-fuel-supported, pro-oil Competitive Enterprise Institute is being undermined by seven state attorneys general and former vice president Al Gore because of the latter group’s initiative and advocacy for clean power generation. Would the CEI ignore all the information out there regarding the damaging effects of the fossil-fuel industry spewing carbon into the atmosphere and warming the planet at an alarming rate?

World governments have every right to petition for access to information from various entities that could benefit from a solution to the most serious problem facing the existence of life on this planet: global warming. We are already experiencing tragic results with floods, droughts, fracking-generated earthquakes and poisoned drinking water.  

I have no sympathy at all for Mr . Kazman and Mr. Lassman!

Dee Foscherari, Washington