Pope Francis has made great efforts to make people aware of the phenomenon of climate change. In his encyclical, Laudato Si’, the pope calls the climate, “a common good belonging to all and meant for all.” He states that, “a very solid scientific consensus indicates that we are presently witnessing a disturbing warming of the climatic system.” To understand the issue of climate change it is important to look at the basic science involved. There is distinction between weather and climate.
Weather refers to the conditions in the atmosphere, such as temperature, precipitation, humidity, wind, etc., over a short period of time as in minute-to-minute, hour-to-hour, or day-to-day. Climate, on the other hand, is how the atmosphere behaves over a relatively long period of time. For example, we expect the summers here to be warm and the winters to be cold. Our seasons result from the tilt of the earth on its axis (this is why a globe is always tilted on its stand). As the earth orbits around the sun, when the north pole is pointing toward the sun, the northern hemisphere is getting the most direct rays of the sun, and is warmer. The southern hemisphere is cooler because the south pole is pointed away from the sun. As the earth continues to orbit around the sun in the same year, the southern hemisphere will be pointed toward the sun and will be warm while the northern hemisphere will be cool.
The temperature of the earth depends on the amount of energy that the earth receives from the sun and the amount of energy that radiates from the earth back into space. It is our atmosphere that helps determine how much energy reaches the earth, and how much is radiated back out. Our atmosphere is composed of 78 percent nitrogen gas, 21 percent oxygen gas and one percent other gases. Among these other gases are heat trapping gases, known as greenhouse gases, such as carbon dioxide, methane, water vapor, and nitrous oxide. They are called greenhouse gases because they participate in process known as the Greenhouse Effect. Just as sunlight passes through the glass of a greenhouse, radiant energy from the sun can pass through the atmosphere. This energy is absorbed by the material inside the greenhouse. The earth also absorbs the sun’s energy. The energy that radiates from the material in the greenhouse, or the material on earth, is in the form of infrared, or heat, energy. In the greenhouse the heat energy is trapped by the glass, so the greenhouse heats up. The greenhouse gases trap the heat and radiate it back to earth keeping our temperature livable. Without the greenhouse gases the average temperature on the earth would be 32 degrees F (0 degrees C) instead of the current 60.8 degrees F (16 degrees C). As an example, the moon, which has no atmosphere, has a temperature range from 223 degrees F ( 106 degrees C) to -297 degrees F (-183 degrees C). As levels of these greenhouse gases increase, more heat is trapped.
Natural cycles, called Milankovitch cycles, can also vary the amount of the sun’s energy that reaches us. These include changes in the size of the earth’s orbit, changes in the tilt of the earth’s axis and wobble in the earth’s axis. These cycles occur over thousands of years. During the past we have had major ice ages every 100,000 years or so corresponding to these cycles. There are changes in the sun’s activity about every 11 years. Also, the carbon dioxide and particulates from volcanic eruptions have also affected the earth’s climate.
It takes a vast amount of heat to warm all of the oceans, atmosphere, and land, so a 1.8 degree F (1 degree C) change in the average global temperature is quite significant. A 9 degree F (5 degree C) drop resulted in a major ice age 20,000 years ago. Estimates of the temperature and greenhouse gases in the atmosphere over the past 800,000 years are gathered by studying thick ice cores taken from Antarctica. These indicate that the average temperature has risen 9 degrees F (5 degrees C) and fallen 18 degrees F (10 degrees C) in cycles over this period. The level of carbon dioxide in the atmosphere has varied from 180 to 300 ppm.
Over the last 250 years, the earth’s average temperature has risen 2.7 degrees F (1.5 degrees C) with 1.6 degrees F (0.9 degrees C) over only the last 50 years. NASA has studied these changes, as well as the changes in natural cycles, extensively using satellites and surface instruments, and has come to the conclusion that while natural causes are still in play, their influence is too small, or occur too slowly, to explain this rapid warming trend. Since 1850, the start of the Industrial Revolution, we have been using the fossil fuels, coal, oil and natural gas, which have been locked in the earth for hundreds of millions of years, at an incredible rate. The burning of these fossil fuels has resulted in the release of large quantities of carbon dioxide. Farming practices, including increased use of commercial fertilizers, and changes is land use have released additional nitrous oxide and methane. This has added extra insulation to the existing atmospheric blanket and thus capturing more heat.
The Intergovernmental Panel on Climate Change, made up of thousands of volunteer scientists throughout the world, has reported that the scientific evidence for warming of the climate system is unequivocal. Also, the atmospheric concentrations of carbon dioxide, methane, and nitrous acid have increased to levels unprecedented in at least the last 800,000 years. Carbon dioxide concentrations have increased by 40 percent since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions. The carbon dioxide level is now at 400 ppm, a level not seen on earth for one or more million years.
The scientific evidence is overwhelming that climate change is happening, and also, that humans have a big hand in that change. Next time we will look at the consequences of our actions and lack of action related to climate change.
Anchor columnist Professor Rak is a Fall River native and a parishioner of St. Mary’s Parish in Fall River. He has been a professor of Environmental Technology and coordinator of the Environmental Science and Technology Program at Bristol Community College in Fall River for 18 years. He earned a bachelor’s degree in biology from Holy Cross College in Worcester, and a master’s degree in marine biology from UMass Dartmouth. firstname.lastname@example.org