Clouds’ Effect on Climate Change
For decades, a small group of scientific dissenters has been trying to shoot holes in the prevailing science of climate change, offering one reason after another why the outlook simply must be wrong.
Over time, nearly every one of their arguments has been disproved by accumulating evidence, and polls say 97$% of working climate scientists now see global warming as a serious risk.
Yet in recent years, the climate change skeptics have seized on one last argument that cannot be so readily dismissed: Their misguided theory is that clouds will save us.
They acknowledge that the human release of greenhouse gases will cause the planet to warm. But they assert that clouds — which can either warm or cool the earth, depending on the type and location — will shift in such a way as to counter much of the expected temperature rise and preserve the equable climate on which civilization depends.
Their theory exploits the greatest remaining mystery in climate science, the difficulty that researchers have had in predicting how clouds will change. The scientific majority believes that clouds will most likely have a neutral effect or will even amplify the warming, perhaps strongly, but the lack of unambiguous proof has left room for dissent.
With climate policy nearly paralyzed in the United States, many other governments have also declined to take action, and worldwide emissions of greenhouse gases are soaring.
Natural Thermostats
Clouds are so familiar they are easy to take for granted, but scientists point out that they have an enormous effect on the climate.
The energy that drives life on earth arrives as sunlight. To remain at a steady temperature, the earth has to return the energy it receives back to space, primarily as heat. Clouds alter the energy flow in both directions.
On balance, in today’s climate, clouds cool the earth. Dense, low-lying clouds are responsible for most of that effect, because they reflect considerable sunlight back to space. Many high, thin clouds have the opposite influence, allowing incoming sunshine to pass through but effectively trapping heat that is trying to escape.
Humans are perturbing the earth’s heat balance by releasing greenhouse gases. Chemists proved in the 19th century that these gases, especially the carbon dioxide that results from burning fossil fuels, work like an invisible blanket in the atmosphere, blocking some heat that is attempting to escape to space. In the mid-20th century, as it became clear how fast carbon dioxide levels were rising, some scientists began to predict a warming of the planet. But they also realized that an exact forecast was difficult for several reasons, especially the question of how clouds would react.
Researchers are virtually certain the amount of water vapor in the atmosphere will rise with temperature, and evidence suggests this is already happening. But that does not say much about the type or location of clouds that will condense from the vapor.
Scientists use sophisticated computer programs to forecast future climate, but the computers are not yet powerful enough to predict the behavior of individual clouds across the whole earth over a century, which forces the researchers to use rough approximations.
The most elaborate computer programs have agreed on a broad conclusion: Clouds are not likely to change enough to offset the bulk of the human-caused warming. Some of the analyses predict that clouds could actually amplify the warming trend sharply through several mechanisms, including a reduction of some of the low clouds that reflect a lot of sunlight back to space. Other computer analyses foresee a largely neutral effect. The result is a big spread in forecasts of future temperature, one that scientists have not been able to narrow much in 30 years of effort.
The earth’s surface has already warmed about 1.4° Fahrenheit since the Industrial Revolution, most of that in the last 40 years. Modest as it sounds, it is an average for the whole planet, representing an enormous addition of heat. An even larger amount is being absorbed by the oceans. The increase has caused some of the world’s land ice to melt and the oceans to rise.
By midcentury, the level of greenhouse gases in the atmosphere is expected to double compared with the value that prevailed before the Industrial Revolution. At the low end, computers predict that the earth could warm in response by another 2° Fahrenheit. The likelier figure, the analyses say, is 4°. At the high end of projections, the warming could exceed 8°. In all possible outcomes, the warming over land would be roughly twice the global average, and the warming in the Arctic greater still.
Even in the low projection, many scientists say, the damage could be substantial. In the high projection, some polar regions could heat up by 20 or 25° Fahrenheit — more than enough, over centuries or longer, to melt the Greenland ice sheet, raising sea level by a catastrophic 20 feet or more. Vast changes in rainfall, heat waves and other weather patterns would most likely accompany such a large warming.
A major goal of climate research is to improve the way clouds are represented in the computer analyses, which should narrow the range of predicted temperatures. And some of the most important data that researchers need to do so are streaming from a hilltop in rural Oklahoma, near the town of Lamont, where the Department of Energy runs the world’s largest facility for measuring the behavior of clouds.
The questions that scientists still need to answer are voluminous. For instance, they want a better idea of how clouds form at a microscopic scale, how their behavior varies under different atmospheric conditions, and how sensitive they are to higher temperatures.
Recently, million of dollars worth of new radars have been installed across America at weather stations and research facilities, promising a better view of the innards of clouds. Satellites are also supplying better data, and theories of the atmosphere are improving.
But the problem of how clouds will behave in a future climate is not yet solved — making the unheralded field of cloud research one of the most important pursuits of modern science.
Too Late?
Ultimately, as the climate continues warming and more data accumulate, it will become obvious how clouds are reacting. But that could take decades, scientists say, and if the answer turns out to be that catastrophe looms, it would most likely be too late. By then, they say, the atmosphere would contain so much carbon dioxide as to make a substantial warming inevitable, and the gas would not return to a normal level for thousands of years.
