Greenhouse effect and global warming
Small amounts of carbon dioxide and water vapour, as well as trace amounts of ozone, methane, nitrous oxide, chlorofluorocarbons, and other gases in the troposphere, play a key role in determining Earth’s average temperatures and thus its climates.
Collectively, these gases, known as greenhouse gases, act somewhat the glass panes of a greenhouse. They allow light, infrared radiation, and some ultraviolet radiation from the sun to pass through the troposphere. Earth’s surface adsorbs much of this solar energy and degrades it to longer-wave, infrared radiation – that is, heat – which then rises into the troposphere. Some of this heat escapes into space; some is adsorbed by molecules of greenhouse gases, warming the air; and some radiates back toward Earth’s surface. This natural trapping is called the greenhouse effect.
The primary heat-trapping gas in the atmosphere is water vapour, because its concentration in the atmosphere averages 1-5%, inputs of water vapour from human activities have little effect on this chemical’s greenhouse effect. By contrast, because the concentration of carbon dioxide in the atmosphere is so small (0.036%), the fairly large input of CO2CO2
carbon dioxide from human activities can significantly affect the amount of heat trapped in the atmosphere.
The basic theory behind the greenhouse effect is well established, satellites equipped with infrared detectors have measured the effect of greenhouse gases on outgoing infrared radiation. Indeed, without greenhouse gases (especially water vapour), Earth would be a cold and lifeless planet with an average surface temperature of -18oC instead of its current 15oC. We and other species currently benefit from a comfortable level of greenhouse gases that typically undergo only minor, slow fluctuations over hundreds to thousands of years. However, crude but improving mathematical models of Earth’s climate indicate that global warming taking place over a few decades, whether from natural causes or because of humans’ emissions of gases into the atmosphere, could be disastrous for human societies and many forms of life.
Ozone (O3) is formed in the stratosphere as the sun’s ultraviolet rays interact with oxygen molecules (O2). Normally, the rate at which ozone is destroyed in the stratosphere equals the rate at which it is formed, so that the average concentration remains about the same. Besides preventing at least 95% of the sun’s harmful ultraviolet radiation from reaching the Earth’s surface, stratospheric ozone creates warm layers of air that prevent churning gases in the troposphere from entering the stratosphere. The “thermal cap” is important in determining the average temperature of the troposphere and thus Earth’s current climates.
Today, there is no doubt that, as a result of the growing amount of greenhouse gases, climate change is an indisputable fact.
Scientists agree that the earth’s rising temperatures are fueling longer and hotter heat waves, more frequent droughts, heavier rainfall, and more powerful hurricanes.
The earth’s ocean temperatures are getting warmer, too – which means that tropical storms can pick up more energy. In other words, global warming has the ability to turn a category 3 storm into a more dangerous category 4 storm. In fact, scientists have found that the frequency of North Atlantic hurricanes has increased since the early 1980s, as has the number of storms that reach categories 4 and 5. The 2020 Atlantic hurricane season included a record-breaking 30 tropical storms, 6 major hurricanes, and 13 hurricanes altogether. With increased intensity come increased damage and death.
The impacts of global warming are being felt everywhere. Extreme heat waves have caused tens of thousands of deaths around the world in recent years. And in an alarming sign of events to come, Antarctica has lost nearly four trillion metric tons of ice since the 1990s. The rate of loss could speed up if we keep burning fossil fuels at our current pace, some experts say, causing sea levels to rise several meters in the next 50 to 150 years and wreaking havoc on coastal communities worldwide.
