This planet is gradually warming, mainly because of the burning of fossil fuels, which add heat-trapping gases to Earth’s atmosphere. The increased temperature changes the climate in other ways too, including the rise in sea levels; ice mass loss in Greenland, Antarctica, the Arctic and mountain glaciers worldwide; shifts in flower blooming; and extreme weather events.
Life on Earth is dependent on a layer of gases, primarily water vapor, in the lower atmosphere that trap heat from the sun, while radiating some of it back and keeping our planet at a temperature capable of supporting life.
The sunshine that remains trapped is our source of energy and is used by plants in photosynthesis, whereas the remainder is reflected as heat or light back into space. Climate forcing (or “radiative forcing”) is the differential between the amount of sunlight absorbed by Earth and the amount of energy radiated back to space.
Several factors determine the size and direction of this forcing; for example light surfaces are more reflective than dark ones, so geographical regions covered by ice and snow reflect back more than areas covered by dark water or dark forests; this variable is called the “albedo effect.”
Human activity is currently generating an excess of long-lived greenhouse gases that don’t dissipate in response to temperature increases, resulting in a continuing buildup of heat. They retain more heat than other gases because they are more transparent to the incoming sunlight than to infrared radiation, which is the form in which heat is radiated back out. Consequently, if the amount of greenhouse gas increases, more heat is trapped in the lower part of the atmosphere, warming the whole planet.1
The greenhouse gases include water vapor, carbon dioxide, nitrous oxide, ozone, and various fluorocarbons. Although water vapor is the most abundant of these gases, it is not much affected by human activity. The climate effects that must concern us are mainly caused by the gases that contain carbon. Carbon dioxide is especially worrisome; its natural sources include the decomposition of living organisms and animal respiration. The main source of excess carbon dioxide emissions is the burning of fossil fuels, while deforestation has reduced the amount of plant life available to turn CO2 into oxygen.
The quantity of greenhouse gas varies over time; for example, there are seasonal variations. The amount of carbon dioxide in the northern hemisphere increases somewhat in the autumn and winter but decreases in the spring. This happens because plants take in carbon dioxide when they are growing but release it when their leaves fall off and decay.
The composition of Earth’s oceans, land, atmosphere, and plants change continuously. For example, gases can dissolve in the ocean, but they also can evaporate and move around in the wind. At present, the oceans are absorbing slightly more carbon dioxide than they are emitting. The amount of carbon being held inside plants varies; when forests are replaced by annual crops, less of it is contained in plants, so more of it is in the air. The more of it in the air, the more the planet warms. Our warming climate is also creating a feedback loop, a “vicious cycle,” by releasing greenhouse gases trapped in Arctic permafrost, thereby warming the planet even more.2
If you’ve paid attention to the alarming weather reports throughout the past few decades, you’ll prefer to keep more greenhouse gas “locked up” instead of circulating in the atmosphere.
Whenever a greenhouse gas is locked up, kept out of circulation, it is said to be “sequestered” in a “carbon sink.”3 The ocean is currently a carbon sink because it is absorbing more carbon dioxide than it is emitting. Soil and forests are also great carbon sinks that could sequester even more carbon than at present without being saturated. Unfortunately, today they often are instead “carbon sources” because of the way human beings are mis-using them. When more trees are being felled than grown, and when land is eroding or being flooded, those forests and soil are carbon sources – releasing more greenhouse gas to the atmosphere than they take in and sequester.
There are other important carbon sources too: notably “fossil fuels.” Thousands of years ago large carbon sinks (dead plants and animals) happened to become buried and turned into oil, coal, or methane (a carbon-based greenhouse gas). Then in the eighteenth century, the Industrial Revolution began in Britain. Machines were developed on a large scale for manufacturing and transportation. These new technologies have spread so widely that global civilization today is dependent on energy produced by burning coal, gas, or petroleum products, though doing so releases more and more greenhouse gas into the atmosphere, thereby heating up the planet.
A little additional heat can make a large difference. Already Earth is almost one degree Celsius hotter than during pre-industrial times,4 and if nothing is done to change the trend, it may become as much as four degrees hotter within the foreseeable future, leading to the catastrophic extinction of life forms.
There are two ways to prevent this: (a) reduce the new emissions of greenhouse gas, and (b) increase the capture and sequestering of greenhouse gas into carbon sinks. Both will require drastic and urgent changes to our current lifestyle, but they should already be underway, reducing the amount of greenhouse gas in the atmosphere. Regrettably, however, many people still even deny that there is a problem, sometimes adducing as evidence the snow outside their windows.
The local weather on any given day proves nothing about the global climate. When the planet warms, the additional heat is not distributed evenly around the globe. Ocean and wind currents are circulating constantly. When, for example, glaciers and polar ice melt, the fresh water flows into the ocean, raising the sea level and possibly changing the direction of ocean currents in ways that alter the climate in many localities. More extreme weather events occur — not only heat waves, droughts, and forest fires, but also blizzards, typhoons, hurricanes, and floods.5 Thousands of measurements must be collected from all parts of the world to get an overall picture of the climate as it changes. The greenhouse gases are constantly flowing and mixing. With the exception of air samples from, say, highways or industrial zones, the amount of greenhouse gas in the atmosphere tends to be similar around the world. There is nowhere to hide from global warming.
In this section we will be exploring several proposals for changes that will each reduce these climatic threats and help to save humankind and our world.
2 Margaret Kriz Hobson. “Melting Permafrost Could Affect Weather Worldwide; It’s not just releasing greenhouse gases—it may also alter the ocean’s chemistry and circulation patterns”. Scientific American, December 1, 2016. https://www.scientificamerican.com/article/melting-permafrost-could-affect-weather-worldwide/
3 “What is a Carbon Sink?” Andrea Thompson | December 21, 2012. https://www.livescience.com/32354-what-is-a-carbon-sink.html
4 Climate Analytics, “Global warming reaches 1°C above preindustrial, warmest in more than 11,000 years” https://climateanalytics.org/briefings/global-warming-reaches-1c-above-preindustrial-warmest-in-more-than-11000-years/
5 Extremely Bad Weather: Studies start linking climate change to current events. Science News, Vol.182 No.10: November 17, 2012.