Climate Forcings and Feedbacks
For convenience and clarity, climate scientists separate things that affect climate change into two categories, forcings and feedbacks. Radiative forcing is generally defined as the change in net irradiance between different layers of the atmosphere. It is a way to quantify an energy imbalance imposed on the climate system either externally or by human activities. Climate forcings are different factors that affect the Earth's climate. These "forcings" drive or "force" the climate system to change, according to the National Oceanic and Atmospheric Administration (NOAA). There are natural forcings and man-made forcings. A positive forcing (more incoming energy) tends to warm the system, while a negative forcing (more outgoing energy) tends to cool it. Climate feedbacks are processes that change as a result of a change in forcing, and cause additional climate change. A feedback that increases an initial warming is called a 'positive feedback.’ A feedback that reduces an initial warming is a 'negative feedback.'
The forcings that were probably the most important during the last millennium were: changes in the output of energy from the sun, volcanic eruptions, and changes in the concentration of greenhouse gases in the atmosphere. The National Aeronautics and Space Administration (NASA) Goddard Institute for Space Studies’ (GISS) graph images of the radiative forcings and the net forcings shows the changes in effectiveness of the main radiative forcings since 1880. In the radiative forcings graph image, greenhouse gases are shown to have the greatest sustained positive forcing on the climate system. Stratospheric aerosols from volcanic eruptions can also have a strong, negative cooling influence, but it is very short term. There is a small influence of solar irradiance changes since 1880. However, the indirect cooling impact of the release of man-made aerosols is also having a significant impact. In the NASA GISS image that shows the overall Net Forcing since 1880, one can clearly see the trend toward the positive, which is clearly due to the increasing amount of well-mixed greenhouse gases into the Earth's atmosphere. (http://data.giss.nasa.gov/modelforce/)
As the PBS Global Climate Change webpage stated, “…the National Academies examined the knowledge regarding the climate forcings associated with gases, aerosols, land use, and solar variability and to identify relevant research needs.” Solar irradiance, aerosols, dust, smoke, and soot are examples of forcings occurring today. Clouds, the carbon cycle, ocean circulation, precipitation, and sea level rise are examples of specific feedbacks.
Aerosols, dust, smoke, and soot is the forcings category that is prevalent here in Las Vegas. These come from both human and natural sources. They also have very different effects on climate. Sulfate aerosols, which result from burning coal, biomass, and volcanic eruptions, tend to cool the Earth. The reason that aerosols is more prevalent here in Vegas is because of the big coal mining industry here and the constant flux of people coming here and emitting poisonous gas fumes from their vehicles. Basically, it is because of the overproduction of fossil fuels. Blackstone Group LP, NV Energy, and White Pine Energy Associates are all energy giants that have coal-fired power plants here in Nevada.
As the Global Climate Change articles stated, “Increasing industrial emissions of sulfates is believed to have caused a cooling trend in the Northern Hemisphere from the 1940s to the 1970s. But other kinds of particles have the opposite effect. The global distribution of aerosols has only been tracked for about a decade from the ground and from satellites, but those measurements cannot yet reliably distinguish between types of particulates. So aerosol forcing is another substantial uncertainty in predictions of future climate.”
Currently, natural processes such as the carbon cycle remove about half of each year's human carbon dioxide emissions from the atmosphere, although this varies a bit year to year according to the Global Climate Change article. However, the forcings is causing loss of carbon from terrestrial ecosystems, leading to an increase of atmospheric carbon dioxide levels. Desertification is the degradation of land in dry lands caused by a variety of factors, such as climate change and human activities and it is one of the most significant global environmental problems, according to Helmut Geist. The “Biological Feedbacks in Global Desertification” article stated that desertification is a consequence of global warming in some environments. Desert soils, which Las Vegas is nothing but desert, contain little humus, and support little vegetation. As a result, transition to desert ecosystems is typically associated with excursions of carbon. In the article by Nature News, “Greenhouse effect has 'significantly dried' the western United States”, it stated that snowpack in mountain ranges such as the Rockies is diminishing, average minimum temperatures are rising, and spring run-off in major rivers such as the Colorado river is happening earlier. All these changes seem set to make dry summers even harsher for residents of thirsty cities such as Las Vegas in Nevada. Therefore, there is a serious concern in Las Vegas that there is an unbalance in carbon dioxide. As the Global Climate change article stated, “There is also some evidence that the ability of the Earth system to continue absorbing carbon may decline as the world warms, leading to faster accumulation in the atmosphere.” This seems to be the case here in Las Vegas.
The resources I have located to help me and my students understand climate forcings and feedbacks are:
This video segment adapted from NOVA/FRONTLINE examines the greenhouse effect, its role in keeping Earth habitable, and the industrial changes that have led to an increase in the planet's average temperature
This video segment adapted from NOVA/FRONTLINE demonstrates the physical property of carbon dioxide that causes the greenhouse effect
Students examine the issue of global warming. They calculate how much carbon dioxide all the machines they use produce in one day.
Lesson Plan for Grades 9-12
In this media-rich student activity, learn about the causes and impacts of global warming, as well as potential solutions, and then plan to produce a video response to this pressing issue.
Students study past climate change, explore the effect of greenhouse gases on Earth's atmosphere today, and consider human impact on global warming.
This video segment from Race to Save the Planet: "Only One Atmosphere" discusses the greenhouse effect and global warming
A Global Journey
60.00Interactive/Online Activity
Investigate the roots and hazards of climate change while exploring this interactive world map by topic or by region. Learn about the causes and effects of global warming, the search for solutions and what humans can do to remedy the problem
Asia and Africa: Living on the Edge
60.00Video
Uncover the devastating effects of climate change in Asia and Africa. Focus on the melting Himalayan glaciers, which feed the region's great rivers, drought-stricken Africa and the warming waters of the South East Atlantic
Research resources:
Schlesinger, W. H.; Reynolds, J. F.; Cunningham, G. L.; Huenneke, L. F.; Jarrell, W. M.; Virginia, R. A.; Whitford, W. G. (1990). "Biological Feedbacks in Global Desertification". Science 247 (4946): 1043.
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