- 1.0. Introduction
- 2.0. The Greenhouse Gas Effect
- 3.0. Oceans and Forests Absorb Carbon
- 4.0. Climate Change or Global Warming?
- 5.0. Effects of Climate Change
The world we live in is in a constant state of change. While our climate has undergone many significant shifts in the past, scientists believe that the human influenced nature and the rate of climate change today is unprecedented, and that it is due largely to human activity. Climate instability and a warming planet are especially problematic for small island nations such as Kiribati, Tokelau, and Tuvalu. They are highly susceptible to extreme weather events and sea level rise, and have limited options for adaptation.
Global climate change is a complex topic. The information below outlines its main elements as currently understood by scientists. This information is intended to be a starting point for further investigation rather than a comprehensive guide. For an excellent resource specifically tailored to students, please visit the Environmental Protection Agency (EPA).
The Greenhouse Gas Effect
The greenhouse effect is a natural process by which gases in the atmosphere trap heat from the sun. The gases involved in this process include water vapor, carbon dioxide, methane, and ozone. The effect is similar to a car that is left in the sun all day. The car heats up from the sunlight that passes through the windows. This heat is absorbed by the upholstery of the seats and the floor carpet. While some of this ensnared heat is able to escape, much of it is trapped inside the car.
The greenhouse gas effect benefits our earth because otherwise the lower atmosphere and surface would be too cold to sustain life. Click here for an animated explanation of the greenhouse gas effect.
Gases Absorb Radiation
In the last two hundred years (since the Industrial Revolution), humans have burned more and more fossil fuels, resulting in the release of added carbon dioxide into the atmosphere and intensifying the greenhouse gas effect. Coal-fired power plants and vehicle emissions form the bulk of carbon dioxide (CO2) emissions. Methane (CH4) from landfills and cattle digestion also contribute significantly. Nitrous oxide (NO2) - derived mainly from fertilizers and halocarbons (gases containing fluorine, chlorine, and bromine) - are additional contributors. Halocarbons are found in aerosols and refrigerants. All of these gases are invisible and absorb infrared radiation (heat radiated off the earth once it is warmed by incoming sunlight), causing an increase in global surface temperature.
Intergovernmental Panel on Climate Change
The UN's World Meteorological Organization found that the first decade of the 21st century was the warmest decade since reliable records started in 1850.
The 2007 IPCC report concluded that during the 21st century, world temperatures could rise between 2.0 and 11.5 degrees.. This report also concluded that “The warming of the climate system is unequivocal.” Atmospheric levels of carbon dioxide (the main heat trapping greenhouse gas), have risen to 385 parts per million - up from 280 parts per million in 1850. While some carbon dioxide is emitted through natural processes, this sharp spike since 1850 can be traced to a rise in fossil fuel combustion, widespread deforestation, and industrialization. Historically, industrialized nations have produced the bulk of greenhouse gas emissions, therefore there is controversy on how to limit emissions in the future.
Oceans and Forests Absorb Carbon
Within a balanced ecological system, the earth naturally absorbs some atmospheric carbon dioxide through the ocean. Yet, the sea’s capacity to store carbon is limited. Vegetation utilizes carbon dioxide through the process of photosynthesis. However, widespread deforestation has reduced the number of trees that photosynthesize. Every year, the net loss of forests is estimated at 18 million acres, with 4,500 acres destroyed per hour (UN Food and Agriculture Organization, Forest Dept). This excess carbon overflows into the atmosphere and creates this imbalance. Click here for more information on the carbon cycle.
Climate Change or Global Warming?
The climate system is complex, and region-by-region affects change differently. The trend of rising global surface temperature is commonly referred to as global warming. It has produced a pattern of climate disruption that varies by location. For instance, warmer temperatures lead to increased evaporation from oceans. This leads to more infrared radiation within the atmosphere and that results in the rising of temperatures. All of the effects of these climate changes are not predictable. In some regions water evaporation might result in increased cloud cover and actually decrease surface temperatures. For these reasons scientists prefer the term Climate Change rather than Global Warming.
Effects of Climate Change
Sea Level Rise
Thermal expansion is currently the greatest contributor to sea level rise. Simply put, when water is heated, it expands. Higher sea levels can result in greater flooding and storm surges, coastal erosion, contamination of fresh water supplies, destruction of public infrastructure, personal property, and loss of animal habitat. Small increases of a few feet could flood low-lying nations and threaten the livelihoods of millions of people.
Sea level rise not only affects small island nations such as Kiribati, Tokelau, and Tuvalu, but also many of the world’s most populous cities and fertile delta regions (New Orleans, Florida, and the Netherlands, for instance).
Sea levels have varied historically over time. Since the ice age, water levels have risen by over one hundred feet. For many years, sea levels had remained relatively constant. Since the mid-19th century, though, sea levels have increased about seven inches. This may be due to natural variation, but many scientists attribute it to human-induced climate change. The 2007 IPCC Climate Change Report estimates that sea levels will probably rise by another 7.1 to 23 inches in this century. Click here to use this interactive sea level rise tool to see how regions will be affected under different scenarios.
The world’s glaciers cover nearly 10% of Earth’s land area. Warmer winter temperatures mean that snow cannot replace the loss of glacier ice. Glaciers serve as important fresh water sources and people depend on glacial flows to irrigate crops and provide hydroelectric power and drinking water. Decreased water flows not only disrupt these essential human needs, but also raise the overall sea level.
Acidification of the Oceans
The ocean is a carbon sink, meaning that it absorbs CO2 from the atmosphere. Hydrogen atoms from CO2 lower the pH of the water, making it more acidic. Increased levels of acidity impede the ability of ocean organisms to form hard shells and skeletons from calcium carbonate and may be tied to coral bleaching. Click here to learn more about Ocean acidification.
Extreme Weather Events
Beginning in 1970, scientists have noted increased tropical storm activity in the North Atlantic. Documentation has shown that the frequency, intensity, and duration of extreme weather events are evident. Tropical storms intensify when surface water temperature and humidity increase. The number and severity of heat waves since 1950 has also increased. Additionally, the extent of regions affected by drought has also risen. Globally, the numbers of heavy daily precipitation events that lead to flooding have increased.
Although it is hard at this point to confidently attribute such extreme events to recent climate warming, in 2007, IPCC climate change scientists stated with 90% confidence that there will be more frequent warm spells, heat waves, heavy rainfall, droughts, tropical cyclones, and extreme high tides.
Disruption of Ecosystems
Increases in surface temperatures change ecosystems forever, such as the thawing of permafrost in the Arctic to the shrinking of glaciers. A recent study in the journal Nature observed that both plants and animals across the globe have been shifting their geographic distributions in response to changes in temperature.
Spread of Tropical Disease
An increase in temperature expands the range of biting insects, increases their breeding rates, and accelerates the maturation of the pathogens they carry. Populations who had no previous exposure to malaria, dengue fever, and yellow fever are being affected by diseases heretofore unknown to them.
Certain populations, regions, and ecosystems are disproportionately affected by climate change. The most vulnerable are people with limited incomes who are directly dependent on natural resources, and have few social, political, and economic safety nets. Disruptions in weather patterns are expected to be the most severe in the Arctic, Africa, the large river deltas in Asia and Africa, and small island nations (like Kiribati, Tokelau, and Tuvalu).