President Ronald Reagan (right) with George Shultz (left), who served as secretary of state under Reagan from 1982 to 1989. (Courtesy of Hoover Institution)

George P. Shultz was secretary of state from 1982 to 1989.

The trend of disappearing summer sea ice in the Arctic is clear even though there is always some variability from year to year. Severe winter weather underscores the importance of keeping track of significant trends. Here are the numbers, according to Julienne Stroeve, of the National Snow and Ice Data Center in Boulder, Colo., as reported in the Economist in February:

“Between 1953 and 2014, the average area of the Arctic sea ice shrank by 48,000 square kilometers a year.”

“Between 1979 and 2014, it shrank by 87,000 square kilometers a year.”

“Between 1996 and 2014, the rate rose to 148,000 square kilometers.”

The accelerating rate is explained in part by the fact that ice reflects sunlight but water, which is darker, absorbs it. So as water replaces ice, more heat is retained. Heat transported from lower latitudes could also be part of the explanation.

The picture in Greenland is more complicated, but it is important in the long run. Arctic ice is already in the water, so melting there won’t make much of an impact on sea levels. Greenland, though, is home to the world’s second-largest land ice mass. Two satellites measure annual melting in Greenland; over the past two decades its net ice loss has been about 140 billion tons per year, and that rate has almost doubled in more recent years. The story is similar in West Antarctica, where surface geography makes it easier for large segments of its ice sheet to slide into a warming ocean. Altogether, we can observe that sea levels are now rising about 3 millimeters per year. We can also observe that the last time the earth warmed by a few degrees — 120,000 years ago — sea levels were at least 5 meters higher than today.

Temperatures vary. You may have read about a global “stall” in temperature increase over the past decade, despite carbon dioxide levels rising at about 0.5 percent each year. Here again, though, trends tell the bigger story. Since humans started to produce more CO2 in the late 1800s, we know that overall land and ocean temperatures have increased about 1 degree Celsius, and in Antarctica, teams examining the world’s oldest ice cores recently released their findings of 800,000 years of climate history. “Even when our climate was in some other phase, some different way of balancing the many subtle influences that make up the wind and weather and warmth we experience, temperature and greenhouse gases still marched in lockstep,” wrote Gabrielle Walker in her book “Antarctica: An Intimate Portrait of a Mysterious Continent.” “Higher temperature always went with higher CO2. Lower temperature went with lower CO2.”

These are simple and clear observations, so I conclude that the globe is warming and that carbon dioxide has something to do with that fact. Those who say otherwise will wind up being mugged by reality.

I am also impressed by an experience I had in the mid-1980s. Many scientists thought the ozone layer was shrinking. There were doubters, but everyone agreed that if it happened, the result would be a catastrophe. Under these circumstances, President Ronald Reagan thought it best not to argue too much with the doubters but include them in the provision of an insurance policy. With the very real potential for serious harm, U.S. industry turned on its entrepreneurial juices, and the Du Pont company developed a set of replacements for the chemicals implicated in the problem along a reasonable time frame and at a reasonable cost. It came up with something that could be done then — not some aspirational plan for 2050. Action is better than aspiration. As matters turned out, the action worked and became the basis for the Montreal Protocol, widely regarded as the world’s most successful environmental treaty. In retrospect, the scientists who were worried were right, and the Montreal Protocol came along in the nick of time. Reagan called it a “magnificent achievement.

We all know there are those who have doubts about the problems presented by climate change. But if these doubters are wrong, the evidence is clear that the consequences, while varied, will be mostly bad, some catastrophic. So why don’t we follow Reagan’s example and take out an insurance policy?

First, let’s have significant and sustained support for energy research and development. More of that is going on right now than in any previous period. The costs to the federal budget are small — little more than a rounding error — and a serious government effort would attract private capital from investors who want to know what’s new and want to contribute. These efforts are producing results. For example, we can now produce electricity from the wind and the sun at close to the same price we pay for electricity from other sources, and we may soon know how to do cost-effective large-scale storage of electricity, thus greatly reducing the intermittency problems of solar and wind and producing a hedge against the great vulnerability of our power grid.

Second, let’s level the playing field for competing sources of energy so that costs imposed on the community are borne by the sources of energy that create them, most particularly carbon dioxide. A carbon tax, starting small and escalating to a significant level on a legislated schedule, would do the trick. I would make it revenue-neutral, returning all net funds generated to the taxpayers so that no fiscal drag results and the revenue would not be available for politicians to spend on pet projects.

These two policies could be put in place in conjunction with eliminating burdensome existing laws and regulations and using the marketplace rather than edicts by the government to do this or not do that. Put a price out there, and let the marketplace adapt. You would be surprised at its creativity.

So that is my proposal. Before you get mugged by reality, take out an insurance policy. It’s the Reagan way.