5 Global Atmospheric Changes

Jean Brainard

What is Climate

Traditionally, climate has been defined as the average weather: temperature, precipitation, cloudiness, and how these variables change throughout the year. Now, earth-system science leads to a much broader definition.

For many, the term “climate” refers to long-term weather statistics. However, more broadly and more accurately, the definition of climate is a system consisting of the atmosphere, hydrosphere, lithosphere, and biosphere. Physical, chemical, and biological processes are involved in interactions among the components of the climate system. Vegetation, soil moisture, and glaciers, for example, are as much a part of the climate system as are temperature and precipitation. Pielke (2008).

The Ocean Strongly Influence Earth’s Present Climate

The ocean drives the atmospheric circulation by heating the atmosphere, mostly in the tropics.

  1. Most of the sunlight absorbed by earth is absorbed at the top of the tropical ocean. The atmosphere does not absorb much sunlight. It is too transparent. Think of a cold, sunny, winter day at your school. All day long, the sun shines on the outside, but the air stays cold. But if you wear a black coat outside and stand out of the wind, the sun will quickly warm up your coat. Sunlight passes through the air and warms the surface of the ocean, just as it warms the surface of your coat. Most of the ocean is a deep navy blue, almost black. It absorbs 98% of the solar radiation when the sun is high in the sky.
     Heating of earth’s surface by solar radiation, in W/m2, calculated from the ECMWF 40-year reanalysis of atmospheric data. Notice that most of the heat absorbed by earth goes into the tropical ocean. From Kallberg et al 2005.
  2. The ocean loses heat by evaporation (the technical term is latent heat release). Think of this as the ocean sweating. Trade winds carry the evaporated water vapor to the Inter-Tropical Convergence Zone where it condenses as rain. Condensation releases the latent heat and warms the air. Warm air rises, further drawing in warm wet air, releasing more heat. Large areas of the tropical ocean get more than 3 m (115 inches) of rain each year (8 mm/day in the figure below).
    1. So much heat is released by rain in the Inter-Tropical Convergence Zone that it drives much of the atmospheric circulation. This circulation is called the Hadley circulation.
    2. Heat released by rain in higher latitudes drives storms and winds.
    3. Heat released by rain in hurricanes and thunderstorms drives these storms.
       25-year average of rain rate. From Japan Meteorological Agency, Japanese 25-year Reanalysis (JRA-25) Atlas.
       25-year average of heating of the atmosphere. Notice the high correlation with rain rate shown above. Rain and absorption of infrared radiation heats the atmosphere, mostly in the tropics. This heating drives the atmospheric circulation. From Japan Meteorological Agency, Japanese 25-year Reanalysis (JRA-25) Atlas.


      Upper: Rain in the tropics warms the atmosphere and drives the Hadley circulation. Image from The Why Files.

      Bottom: The Hadley cells (circulation) are a major part of the climate system. Click on image for a zoom. Image from NASA Earth Observatory, Fewer Clouds Found In Tropics.


  3. The ocean also loses heat by sending out infrared radiation (energy), mostly in the tropics. The infrared radiation is absorbed by water vapor in the tropical atmosphere, further heating the atmosphere.
  4. The winds drive ocean currents, and together they carry heat from the tropics to the polar regions. See The Climate System below.

The Ocean Influences Regional Climate

  1. The difference in temperature between the land and the ocean drives monsoons. During the winter, the center of a continent is much colder than the surrounding ocean. This causes cold air to flow out of the continent. During the summer, the center of continent is much hotter than the ocean. This draws moist air into the continent bring much needed summer rains. Monsoon winds are especially important for Asia and North America. Arizona, and the American southwest get summer rains. from the North American monsoon. India gets rain during the Asian monsoon.
     Arizona thunderstorm. Such storms in the American west are common in summer due to the North American monsoon. Click on the image for a zoom. From the National Weather Service Forecast Office Flagstaff Arizona’s article on the monsoon.
  2. Cities along coasts benefit from the sea breeze. It too is due to the difference in temperature between the land and the ocean. During the night the land is cooler, and during the day it is warmer. The contrast in temperature causes winds to blow toward the ocean at night, and toward the land during the day.

Everything Is Connected

From this simple discussion of the climate system, we can conclude that we must understand how earth, with its atmosphere, greenhouse gases, ocean, life, winds, and currents all interact to produce our climate. The ocean is one big part of the earth system. The ocean, atmosphere, and land are connected through the climate system. Changes in one area cause changes everywhere else. Everything is connected, and everything influences everything else.

For example, rain heats the atmosphere. The warm air rises, creating wind. Wind drives ocean currents. Currents help determine where phytoplankton live. Phytoplankton help determine where clouds are formed. Clouds influences where the atmosphere is heated. Heating determines where the ocean evaporates, and the amount of evaporation.

 There are many interacting parts in the earth system.

As a result of these connections:

  1. Earth has a surface temperature that is just right for life. Water vapor from the ocean is essential for setting the earth’s temperature.
  2. The tropical ocean supplies almost all the water that falls on land.
  3. The ocean absorbs half of the carbon dioxide released by our burning of fossil fuels. This reduces global warming caused by carbon dioxide.
  4. So much heat is absorbed by the oceans, that the the warming of earth’s surface by greenhouse gases is slowed down. 84% of the energy available to warm earth’s surface has gone into the ocean during the 48 years from 1955 to 2003; 5% has gone into the land; 4% has gone into the atmosphere; and the remainder has gone into melting ice. (Levitus, 2005).

The Carbon Dioxide Problem

The carbon dioxide problem can be stated relatively simply:

  1. More than six and a half billion people burn fuel to keep warm, to provide electricity to light their homes and to run industry, and to move about using cars, buses, boats, trains, and airplanes.
  2. The burning of fuel produces carbon dioxide, which is released to the atmosphere.
  3. The burning of fuels adds about 6 gigatons of carbon to the atmosphere each year.
  4. Carbon dioxide concentrations in the atmosphere have risen from about 270 parts per million (0.026%) before the industrial age to about 380 parts per million (0.038%) by 2006, a 41% increase over pre-industrial values, and a 31% increase since 1870.
  5. Carbon dioxide is a greenhouse gas, and the increased concentration of carbon dioxide in the atmosphere must influence earth’s radiation balance.

Measurements of Temperature and Carbon Dioxide

Measurements of carbon dioxide can be made at any location on earth remote from nearby local sources because the atmosphere is well mixed over periods of a few years. The two most famous sets of measurements were made at Mauna Loa in Hawai’i and at Vostok station in Antarctica.

  1. Charles Keeling began collecting flasks of air from an observatory at the summit of Mauna Loa in Hawai’i in 1959. Keeling, the first to confirm the rise of atmospheric carbon dioxide by very precise measurements that produced a data set now known widely as the “Keeling Curve.” Prior to his investigations, it was unknown whether the carbon dioxide released from the burning of fossil fuels and other industrial activities would accumulate in the atmosphere instead of being fully absorbed by the oceans and vegetated areas on land. From Charles David Keeling: Climate Science Pioneer.
     This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the Industrial Revolution. (Source: NOAA)
  2. The Vostok ice core is a cylinder of ice collected by drilling from the surface to near the bottom of the Antarctic ice sheet. Total length was 2083 meters, brought back in 4-6 meter sections. The core shows annual layers, which can be used to date the air bubbles trapped in the ice. Analysis of the gas content of the bubbles gives the concentration of carbon dioxide in the atmosphere when the ice formed. Ratios of oxygen isotopes and deuterium gives air temperature at the station at the time ice was formed.
    1.  Atmospheric carbon dioxide concentration calculated from air bubbles trapped in the Antarctic continental glacier and cored at the Vostok ice Station. Notice that present carbon dioxide concentrations far exceed all values for the past 400,000 years, and that the concentration is high when temperature is high. This does not imply cause or effect. Both carbon dioxide and temperature are linked through feedback loops. Both variables change over periods of around 100,000 years due to slow variations in earth’s orbit and spin axis. To learn more about the relation between carbon dioxide and temperature, we need other data and information. Image from UNESCO Introduction to Climate Change, GRID-Arendal.
    2. The page on Evidence for Global Warming has more information on ice cores and other sources of information.

Sources of Anthropogenic (Human-Produced) Carbon Dioxide

Anthropogenic (human-produced) carbon dioxide is mostly from the burning of fossil fuel: coal, oil, and natural gas. The burning of forests to produce agricultural land, and the burning of forest wood for heating and cooking add smaller amounts. The following information comes mostly from the Statistical Review of World Energy 2005 by British Petroleum.

  1. Global energy use from fossil fuels was approximately 8,260 million metric tons oil equivalent, which is approximately 9,623 X 109 m3 = a cube of oil 2.12 km on a side.
  2. Global oil consumption in 2003 was 76,800,000 barrels of oil per day. Most of the remainder of our energy comes from natural gas and coal.
  3. Per capita consumption of energy in the United States is about 57 barrels of oil equivalent per year. The energy is used to heat and light homes, offices, and stores, to power trucks and automobiles, and to operate machinery. 57 barrels of oil at $50/barrel = $2,850. If the energy were used entirely as electricity, it would cost about $7,300 per person per year.
  4. Consumption of energy in the United States was approximately:
    1. 89.4% from burning fossil fuels.
      1. 39.1% oil
      2. 25.9% natural gas
      3. 24.4% coal
    2. 8.1% from nuclear energy
    3. 2.5%from hydroelectric power plants
  5. The United States used approximately 24% of all the world’s energy, although we are only 4.6% of the world’s population.

Anthropogenic sources are a small part of the global carbon system. Their production mixes with carbon dioxide released by the respiration of plants and animals, and through the decay of carbon-based material from plants and animals.

Other Greenhouse Gases

Carbon dioxide is one of several greenhouse gases released in large quantities by human activities. The important gases are:

  1. Water vapor. This is by far the most important greenhouse gas. It evaporates mostly from the ocean, and it causes earth’s surface to be about 30°C warmer (out of the 33°C of warming caused by all greenhouse gases combined). See Ocean and Climate for a discussion of how much water warms the atmosphere.
  2. Carbon dioxide.
  3. Methane. It is produced by bacteria in wetlands and bogs, cattle, rice paddies, termites, landfills, and coal mining. About two thirds of the emissions into the atmosphere come from human activity, mostly in the northern hemisphere. Methane concentration was 1783 parts per billion in 2004, which was 155% larger than pre-industrial concentrations. The rise in methane appears to have leveled off, and concentrations have increased only 5 parts per billion since 1999. Methane does not remain long in the atmosphere, about 8 years (Fischer et al, 2008), so emissions and sinks are already close to balance. One pound of methane is 22 time more effective in absorbing infrered radiation than is a pound of carbon dioxide. The Department of Meteorology at the University of Maryland College Park has a web page listing the amounts emitted by various sources. x
  4. Nitrous oxide, from microbes in the soil and the ocean, and from burning fossil fuels at high temperatures, such as car engines. About one-third of the emissions into the atmosphere come from human activity. N2O concentrations were 319 parts per billion in 2004, which was 18% larger than pre-industrial concentrations. Its lifetime in the atmosphere is similar to that of carbon dioxide, about a century.
  5. Halocarbons such as refrigerants used in air conditioners .
  6. Tropospheric ozone, produced in smog.

How do greenhouse gases influence earth’s surface temperature?

Earth’s average surface is 32°C warmer than it would be if it had no atmosphere. A planet the size of earth at earth’s distance from the sun, and in thermodynamic equilibrium with solar energy (sunlight), would have an average surface temperature of -18°C. Earth’s mean, global surface temperature for the period 1901 to 2000 is 13.9°C, which is 32°C warmer. This increase in temperature is due to greenhouse gases in earth’s atmosphere.

 The greenhouse effect. From the Introduction to Climate Change written by the United Nations Environmental Program’s UNEP Global Resources Information Database (GRID) office in Arendal Norway.


The basic idea is: the atmosphere is transparent to solar radiation. It allows sunlight to reach and warm the earth’s surface. The atmosphere is mostly opaque to infrared radiation emitted from earth’s surface, hindering the emission of radiation from the surface to space, keeping the surface warm.

Now, let’s discuss the details of how greenhouse gases warm earth’s surface. They are:

  1. Sunlight reaches earth. It has an intensity of 1360 W/m2, and the average over all the earth is 343 W/m2. Remember, the average includes day and night, from the equator to the poles. Most solar energy has a wavelength close to 0.5 µm.
  2. 49% of the incoming sunlight goes straight through the atmosphere and it is absorbed by earth’s surface, mostly in the tropical ocean.
  3. 31% of the incoming sunlight is reflected back to space, 22% by clouds, and 9% by the surface.
  4. The remaining 20% is absorbed in the atmosphere.
  5. Sunlight that is absorbed by earth’s surface and atmosphere warms the surface and the atmosphere.

Thus greenhouse gases absorb radiant energy from earth’s surface, and reradiate most of it back to the surface, keeping the surface warm. If there were no greenhouse gases, the surface would rapidly radiate heat away to space. The figure below shows these values a little more clearly.

 The mean annual radiant energy and heat balance of the


What is the Evidence for Climate Change?


Carbon dioxide concentration in the atmosphere measured by David Keeling and colleagues at Mauna Loa, Hawai’i and from polar ice cores, with average global surface temperature of earth. Image from Woods Hole Research Center, presentation by Director John P. Holdren, The Scientific Evidence.

The plot above shows that earth surface is warming. Now let’s look at the evidence used to make the plot.

  1. Where do we get our information?
  2. How do we know if the ocean or land temperatures are changing?
  3. What is the evidence?
  4. How good is the evidence?

Where do we get our information?

  1. On land, temperature is measured a hundreds of weather stations, somewhat unevenly distributed around the world, and on some oceanic islands.
     Map of land stations in the Global Historical Climatology Network where air temperature was measured on land and islands. From: NOAA National Climate Data Center.


  2. At sea, we get data from satellites and from ships. Satellite measurements of surface temperature come primarily from the Advanced Very High Resolution Radiometer (AVHRR) first launched in 1978 and operated continuously since then. The satellite data are calibrated using ship observations of surface temperature from the same time and place. Accuracy of the combined ship and satellite data set, the Reynolds Optimum Interpolation Sea-Surface Temperature maps is about +- 0.3 degrees C on a one-degree (horizontal) grid.
  3. Data from the AVHRR are available with horizontal resolution of about 1 km. Such maps show much more detail than the Reynolds maps. For example, look at a map of sea-surface temperature in the Gulf of Mexico produced by the Johns Hopkins University Applied Physics Laboratory, Ocean Remote Sensing Group. Click on a few of the thumbnails to bring up the image.
    • How was the map made?
    • What problems might we have if we tried to determine average temperature of the ocean before satellites were available, by using data from ships?
    • To learn more, look at the sample images of the Gulf Stream.
  4. Before 1978, all observations at sea were made from ships using thermometers to measure water samples collected in buckets (bucket temperature) or to measure water drawn into the ship to cool the engines (injection temperature). Approximately 185,000,000 observations have been collected, evaluated, and tabulated through the International Comprehensive Ocean Atmosphere Data Set (ICOADS) for the period 1784 to 2002. The data set is the monthly summaries of the observations. The monthly time series are available at 2-degree (1800-2002) and 1-degree (1960-2002) spatial resolutions. Very few observations are available before about 1850, and most are from 1900.
     Number of reports of marine weather reports each year included in the International Comprehensive Ocean-Atmosphere Data Set (From NOAA Climate Diagnostics Center).
 Number of reports of marine weather reports each year included in the International Comprehensive Ocean-Atmosphere Data Set in the period 1936 to 2005 in release 2.3 of the data set. Click on the image for a zoom. From International ICOADS.


Sources of error. Several sources contribute errors to the plot of earth’s surface temperature temperature.

  1. One important error is due to the large variability in the the land and ocean temperature from region to region and month to month. Temperatures on land vary up to approximately 15-20 degrees C during the day at mid latitudes, and by up to approximately 50 degrees C from summer to winter. Over the oceans, the range is much smaller, approximately 7 degrees C from summer to winter.
  2. The biggest error in the calculation is called the sampling error. We do not have enough measurements to determine if temperature is changing before about 1850, and we barely have enough even today. The error leads to some the year-to-year variability in the plot of global averaged surface temperature as as a function of time. Also read about the sampling error in oceanography (scroll down to find the box on sampling error.
  3. Smith and Reynolds report that the 95% confidence uncertainty for the near-global average is 0.48C or more in the nineteenth century, near 0.28C for the first half of the twentieth century, and 0.18C or less after 1950.
     Global average of sea-surface temperature calculated using Smith and Reynolds techniques, with edtimates of errors in the values. From NOAA National Climate Data Center Climate 2005 Annual Report.
  4. Instruments have some error. For example, water in buckets made of canvas used from 1900 to 1940 cooled off quickly compared with water in wooden buckets used before 1900. This introduced systematic, small errors into global averages of sea-surface temperature. See Box 2.2: Adjustments and Corrections to Marine Observations in measurements of sea surface temperature and ocean air temperature in Climate Change 2001.
  5. The urban heat island effect. Most measurements on land are made near cities. As cities grow, they heat the atmosphere over and near the city. This heating is due to the city, not to global warming. About 50% of the warming in the US may be due to heat islands and land use changes (Kalnay, 2003).

Evidence from the past 400,000 years.

The instrumental record based on direct measurements of temperature made by thermometers and satellite instruments goes back only a hundred and fifty years. To learn about more about earlier climate change we need to use proxy data, measurements of phenomena that depend on climate. Various types of proxy data are used:

  1. Cores of the sea floor made by the Integrated Ocean Drilling Program IODP. For example, Expeditions 303 and 306 collected data on climate variability in the North Atlantic over tha past few million years. The data is used with data cores from the Greenland Ice Sheet.
     Location of proposed drill sites. Blue circles = primary sites planned for Expedition 303, red circles = primary sites planned for Expedition 306, and open circles = alternate sites. From Expeditions 303 and 306 Scientific ProspectusIntroduction.
  2. Ice cores from thick ice sheets in Greenland, Antarctica, and mountain glaciers from around the world provide many different types of data:
    1. The layers give the age of the ice. For the latest ten thousand years of longer, counting the layers gives age.
    2. Learn more about evidence collected from ice cores by reading Deciphering Mysteries of Past Climate From Antarctic Ice Cores.
    3. Stable isotopic composition, especially the ratio (18O/16O) where 18O is the concentration of the oxygen 18 isotope, and 16O is the concentration of oxygen 16 isotope, and the concentration of duterium. The oxygen isotope ratio and the duterium concentration give the temperature at which H2O condensed as water or snow on the surface of the ice sheet.
    4. Air bubbles trapped in the ice gives atmospheric gas content, especially the concentration of carbon dioxide.
    5. Dust content in the ice depends on windiness over land upwind of the ice sheet.
    6. Salt content in the ice depends on windiness over the ocean upwind of the ice sheet.
    7. Sulphuric acid content of the ice depends on volcanic activity.
  3. Dendrochronology uses measurements of the width of tree rings to determine relative changes in environmental conditions influencing the growth of trees. Change sin width provide information on droughts and temperature changes. See also dendrochronology at the Minnesota State University’s E-Museum.
  4. Analysis of pollen deposited in layered sediments in lakes gives the type of plants growing in the vicinity of the lake at different times. Types of plants depends on climate, and their types and abundance give information about past climates.

How Serious Is the Threat?

Scientific evidence for warming is convincing. Earth’s surface is warming. The future is less certain. Do we even want to stop global warming?

Given that the climate is changing because of inadvertent consequences of human activities, the question arises as to whether efforts should be made to deliberately change climate to counteract the warming. Aside from the wisdom and ability to do such a thing economically, the more basic question is the ethical one…Who makes the decision on behalf of all humanity and other residents of planet earth to change the climate deliberately? Climate change is not necessarily bad. Frosch and Trenberth (2009).

Our understanding of the importance of global warming depends on the accuracy of climate forecasts. Forecast accuracy depends on how well we understand earth’s carbon cycle, economics, and politics. All influence warming. All are uncertain.

Direct Physical Effects

  • Melting of glaciers and a consequent rise in sea level, already documented
  • Sea level rise of 18-59 cm predicted by 2100
  • River flooding followed by drought
  • Coastal flooding and shoreline erosion

Glacial melting (left) and a rise in sea level (right) are two consequences of global warming. The left image shows the Larsen Ice Shelf B, which broke up during February of 2002 after bordering Antarctica for as long as 12,000 years. Excluding polar ice caps, 50% of glacial areas have disappeared since the turn of the century. Although sea levels have risen since the end of the last Ice Age, rates increased by a factor of 10 beginning about 1900.

  • Melting permafrost, leading to release of bog methane (CH4) increasing warming via positive feedback*
  • Changing patterns of precipitation
  • Regional drought
  • Regional flooding
  • Ocean warming, leading to increased evaporation
  • Increasing rainfall
  • Increasing erosion, deforestation, and desertification
  • Release of sedimentary deposits of methane (CH4) hydrates – positive feedback*
  • Ocean acidification: 0.1 pH unit drop already documented; 0.5 more predicted by 2100
  • Loss of corals
  • Loss of plankton and fish
  • Temperature extremes
  • Increasing severity of storms such as tropical cyclones, already documented
  • Further reductions in the Ozone Layer (due to cooling of the stratosphere)

The proportion of hurricanes reaching category 4 or 5 increased from 20% in the 1970s to 35% in the 1990s. The EPA and the World Meteorological Organization connect this increase to global warming, and NOAA scientists predict a continuing increase in frequency of category 5 storms as greenhouse gases rise.

Ecosystem Effects

  • Contributions to the Sixth Extinction reaching as much as 35% of existing plant and animal species
  • Decline in cold-adapted species such as polar bears and trout
  • Increase in forest pests and fires
  • Change in seasonal species, already documented
  • Potential increase in photosynthesis, and consequent changes in plant species
  • Loss of carbon to the atmosphere due to
  • Increasing fires, which together with deforestation lead to positive feedback
  • Increasing decomposition of organic matter in soils and litter

Socioeconomic Threats Result From Some of the Above Changes

In determining policy, the cost of future damages C due to climate change must be converted to their present value Ct, where:

  1. Present value is the value on a given date of a future payment or series of future payments, discounted to reflect the time value of money and other factors such as investment risk. Present value calculations are widely used in business and economics to provide a means to compare cash flows at different times on a meaningful “like to like” basis. From Wikipedia article on Present Value.

    The present value Ct of a future expense C is calculated from Ct = C (1 + i)–t, where t is the time in years, and i is the cost of money, usually an assumed interest rate that could be earned if the money were invested. The assumed interest rate is controversial because a small change in the rate makes a large difference in the present value if time is several decades or a century. For example, a cost of $1000 that will be incurred in 50 years has a present value of $87.20 if i = 5%, and a value of $54.29 if i = 6%. For more on this problem, read the Hoover Digest article An Economist Looks at Global Warming by Gary S. Becker, who was awarded the Nobel Prize for Economics in 1992.

Possible socioeconomic issues include:

  • Crop losses due to climate and pest changes and desertification
  • Increasing ranges for disease vectors (e.g., mosquitoes – malaria and dengue fever)
  • Losses of buildings and development in coastal areas due to flooding
  • Interactions between drought, desertification, and overpopulation leading to increasing conflicts (Figure below)

A camp in Sudan houses refugees from the far western province of Darfur, who fled from genocide intensified by severe drought. The Darfur conflict echoes predictions that global warming may increase drought and desertification in overpopulated regions and result in more such tragedies.

  • Costs to the insurance industry as weather-related disasters increase
  • Increased costs of maintaining transportation infrastructure
  • Interference with economic development in poorer nations
  • Water scarcity, including pollution of groundwater
  • Heat-related health problems

Threats to Political Stability

  • Migrations due to poverty, starvation, and coastal flooding
  • Competition for resources

Note that at least three(*) of the direct physical effects – melting permafrost, ocean warming, and forest fires/deforestation – can potentially accelerate global warming, because temperature increases result in release of more greenhouse gases, which increase temperatures, which result in more greenhouse gases – a positive feedback system aptly termed a “runaway greenhouse effect.” Here’s how it could work: rising temperatures are warming the oceans and thawing permafrost. Both oceans and permafrost currently trap huge quantities of methane – beneath sediments and surface – which would undergo massive releases if temperatures reach a critical point. Recall that methane is one of the most powerful greenhouse gases, so the next step would be further increase in temperatures. Warmer oceans and more thawed permafrost would release more quantities of methane – and so on. These compounding effects are perhaps the most convincing arguments to take action to reduce greenhouse gas emission and global warming.

What measures have been considered?

Preventing Climate Change

Basically, greenhouse gases are products of fossil fuel combustion; according to the EPA, more than 90% of U.S. greenhouse gas emissions come from burning oil, coal, and natural gas. Therefore, energy use is the primary target for attempts to reduce future global warming. In Figure below you can see the sources of emission for three major greenhouse gases in 2000, when CO2 was 72% of the total, CH4 18%, and NO 9%. Chlorofluorocarbons (CFCs, HCFCs, and HFCs) are also greenhouse gases; refer to the lesson on The Atmosphere for more information about them.

Global greenhouse emissions during 2002 show sources for each of the three major greenhouse gases. Knowing the causes makes finding solutions clear, but not necessarily easy!

Knowing the causes of climate change allows us to develop potential solutions. Direct causes include combustion of fossil fuels, deforestation and other land use changes, cattle production, agriculture, and use of chlorofluorocarbons. Runaway effects can result from temperature-dependent release of methane from permafrost and ocean sediments, and forest fires or intentional burning. Unfortunately, the best way to avoid runaway effects is to prevent temperature increases. Prevention, then, should address as many of these causes as possible. A partial list of solutions being considered and adopted follows.

  1. Reduce energy use.
  2. Switch to cleaner “alternative” energy sources, such as hydrogen, solar, wind, geothermal, waste methane, and/or biomass.
  3. Increase fuel efficiencies of vehicles, buildings, power plants, and more.
  4. Increase carbon (CO2) sinks, which absorb CO2 – e.g., by planting forests.
  5. Cap emissions release, through national and/or international legislation, alone or in combination with carbon offset options (see below).
  6. Sell or trade carbon offsets or carbon credits. Credits or offsets exchange reductions in CO2 or greenhouse emissions (tree-planting, investment in alternative energy sources, methane capture technologies) for rights to increase CO2 (personally, as for air travel, or industry-wide).
  7. Key urban planning to energy use, e.g., efficient public transportation.
  8. Develop planetary engineering: radical changes in technology (such as building solar shades of dust, sulfates, or microballoons in the stratosphere), culture (population control), or the biosphere (e.g. iron-seeding of the oceans to produce more phytoplankton to absorb more CO2).
  9. Legislate Action: International agreements such as the 2005 Kyoto Protocol (which the US has not yet ratified), or national carbon taxes or caps on emissions. Interestingly, in the U.S., some States and groups of States are taking the lead here.
  10. Set goals of carbon neutrality: in 2007, the Vatican announced plans to become the first carbon-neutral state.
  11. Support developing nations in their efforts to industrialize and increase standards of living without adding to greenhouse gas production.

Every potential solution has costs and benefits which must be carefully considered. Human health, cultural diversity, socioeconomics, and political impacts must be considered and kept in balance. For example, nuclear power involves fewer greenhouse gas emissions, but adds the new problems of longterm radioactive waste transport and storage, danger of radiation exposure to humans and the environment, centralization of power production, and limited supplies of “clean” uranium fuels. Studies of costs and benefits can result in solutions which make effective tradeoffs and therefore progress toward the goal of lowering greenhouse gases and minimizing future global warming.

We have reached the point where we understand how and the extent to which our activities have destabilized the Earth’s atmosphere and reduced and threatened its ecosystem services. Now we need to move one step further, and put our knowledge to work in the form of action.

The Precautionary Principle

Faced with the uncertainty in our ability to predict future climate change, many argue in favor of the precautionary principle.

When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically. From The New Uncertainty Principle.

Policymakers need to take a precautionary approach to environmental protection … We must acknowledge that uncertainty is inherent in managing natural resources, recognize it is usually easier to prevent environmental damage than to repair it later, and shift the burden of proof away from those advocating protection toward those proposing an action that may be harmful. From New Jersey governor Christine Todd Whitman In an October 2000 speech at the National Academy of Sciences in Washington, D.C.

The precautionary principle has been interpreted in many ways. In its strongest form

The principle can be interpreted as calling for absolute proof of safety before allowing new technologies to be adopted. For example, the World Charter for Nature (1982) states “where potential adverse effects are not fully understood, the activities should not proceed.” If interpreted literally, no new technology could meet this requirement. From “Science and the Precautionary Principle.”

The strong form stifles progress. If the principle had been applied when fire was invented, we would still be eating our food raw. “If applied to aspirin, it would never have been licensed for sale.” writes Helene Guldberg in Challenging the Precautionary Principle.

The principle is more useful in a weaker form. We need only require that present activity be modified if the future costs of present activity may greatly exceed the cost of changing present activity. For example, if the future cost of climate change may greatly exceed the cost of reducing emissions of greenhouse gases, then we ought to reduce the emissions.

When applied to climate change and global warming the important points are:

  1. We have only one earth.
  2. If greenhouse gas emissions cause large changes in climate, we may not be able to return to our present climate for centuries. CO2 concentrations will remain high for more than 100 years, and temperature will continue to rise even if we stopped all emissions today, even if we do not know how much temperature will rise.
  3. The economic and environmental costs of abrupt climate change far exceed the costs of slowly reducing greenhouse gas emissions (over the next two decades).
  4. Therefore we ought to reduce emissions even if we are not sure they will cause abrupt climate change.
  5. Two decades from now we will know much more about climate change, and at that time we can reassess our activity.

The principle may also apply in trying to reduce greenhouse gas. Reducing greenhouse gas to their pre-industrial level may not return earth to a pre-industrial climate.

In a highly nonlinear feedback-controlled system like global climate, we would expect complex hysteresis effects: Decreasing a control variable such as greenhouse gas will not necessarily lead the climate back along some path like the one it followed when the control variable was increased. The end state of the control-variable manipulation may not at all resemble the original state before the control variable was increased, nor will it necessarily be a state we want to be in. Frosch and Trenberth (2009).

The Kyoto Protocol: A Framework for International Cooperation

Most of the governments of the world, are considering ways to reduce greenhouse gas emissions. The first global step toward reductions was the Kyoto Protocol. On February 16, 2005, the Kyoto Protocol entered into force without ratification by the United States. By July 10, 2006 164 nations and economic regional integration organizations had ratified the Protocol.

  1. What is being proposed? The primary document is the Kyoto Protocol to the United Nations Framework Convention on Climate Change. According to the protocol “The Parties included in Annex I [the developed countries of the world] shall, individually or jointly, ensure that their aggregate anthropogenic carbon dioxide equivalent emissions of the greenhouse gases listed in Annex A do not exceed their assigned amounts, calculated pursuant to their quantified emission limitation and reduction commitments inscribed in Annex B and in accordance with the provisions of this Article, with a view to reducing their overall emissions of such gases by at least 5 per cent below 1990 levels in the commitment period 2008 to 2012.” From Article 3 of the Kyoto Protocol.
  2. How sound are the arguments that support or oppose the proposals?
    1. Read the US Congressional Research Service (CRS) abstract of their report on Global Climate Change: Major Scientific and Policy and the report (104 kByte pdf file) which gives a good overview of the policy issues up to 11 August 2006. The Kyoto Protocol became legally binding on 16 February 2005 at midnight New York time (0500 GMT). The countries that ratified the protocol agreed to cut their greenhouse gas emissions between 2008 to 2012 to levels that are 5.2 per cent below 1990 levels.
    2. Then go the the Energy Information Administration’s Analysis and Report and read about the implications for the US economy.
    3. The United States has ratified the United Nations Framework Convention on Climate Change, but we have not ratified the Kyoto Protocol. The primary reasons for not ratifying the protocol include:
      1. It excludes the world’s most populous countries, China and India, because they are developing countries. The US wanted meaningful participation by all countries.
      2. There is no clear statement of penalties for failure to implement the protocol.
      3. The protocol emphasizes sources of greenhouse gases, but atmospheric concentration depends on sources and sinks. The protocol did not give sufficient weight to implementing new sinks of greenhouse gases. For example, reforestation removes carbon dioxide from the atmosphere. Or, carbon dioxide could be removed from the atmosphere and injected into deep wells. To what extent can which carbon sequestration by forests, soils and agricultural practices be counted toward a country’s emission reductions?
      4. It was not clear how much of a country’s obligation to reduce emissions can be met through purchasing credits from outside, vs. taking domestic action.
      5. The role of emissions trading was not clear. The US would like to use emissions trading to meet a significant percentage of our required reduction in greenhouse gas emissions.
      6. It penalizes the US more than other countries because our economy has been growing strongly compared with other countries that have ratified the protocol.
    4. Although some of these problems were mitigated through later meetings of the Conference of the Parties (COP), the problems are still not completely solved.
    5. Economists point out that the cost of reducing emissions now exceed the cost of reducing emissions in the future when we know more about the consequences of global warming.
    6. Economists also point out that the cost of global warming is about equal to the benefits. Canada and Russia will gain, other economies will lose. “Given reasonable inputs, most cost-benefit models show that dramatic and early carbon reductions cost more than the good they do.”– Stern Review: The dodgy numbers behind the latest warming scare. The Kyoto Protocol is a symbolically important expression of governments’ concern about climate change. But as an instrument for achieving emissions reductions, it has failed. It has produced no demonstrable reductions in emissions or even in anticipated emissions growth. And it pays no more than token attention to the needs of societies to adapt to existing climate change. Time to Ditch Kyoto. Prins (2007)
  3. What are the implications for TAMU students?
     Carbon price needed to meet Kyoto goals in the US. Price increases encourage a reduction in the use of energy services (heating, lighting, and travel, for example), the adoption of more energy-efficient equipment, and a shift to less carbon-intensive fuels. The carbon price reflects the amount fossil fuel prices in the US, adjusted for the carbon content of the fuel, must rise to achieve the removal of the last ton of carbon emissions that meets the carbon reduction target in each case. From; Energy Information Agency. Note: 10 barrels of oil contain about 1 metric ton of carbon. US EPA Green Power Equivalency Calculator Methodologies.

Ways to Reduce Greenhouse gas Emissions

The Kyoto Protocol sets a goal for reducing greenhouse gas emissions. Each country must determine how to reach the goal. Three approaches are taken.

  1. Command and control. The government decides what must be done. For example, the US Congress is proposing to set limits on gasoline mileage for cars. This approach is rarely effective. Drivers in the US switched from small cars to large, less-fuel efficient cars, despite government regulations on fuel efficiency, because the larger vehicles are safer and they are able to carry children and sport equipment used by children. Historical experience since 1800 shows that increased energy efficiency usually leads to more energy consumption.
  2. Economic incentives. European and other governments provide economic incentives such as reduced taxes and funding to those who produce electricity from wind turbines or solar cells.
  3. Use market-based incentives such as taxation to encourage reductions. For example, tax the emission of green-house emissions, allowing each user to determine how best to avoid the tax. This is the approach preferred by economists. The market place is almost always wiser than any politician or government, and it can act much faster and more efficiently.

The different approaches have very different costs, and governments often make popular but costly choices.

 The cost of different ways to cut emissions of carbon dioxide in euros per ton of carbon dioxide. Insulation improvements are the least expensive, and switching from coal to gas for production of electricity is one of the most expensive. From The Economist, 3 June 2007 page 9.


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