Causes and Consequences of a Warming Planet

AgMRC Renewable Fuels Monthly Report
December 2015
Don HofstrandDon Hofstrand
retired economist
Iowa State University

We are bombarded daily with information about global warming.  Most of it comes to us in bits and pieces though media outlets like newspapers and television.  Our challenge is to understand how this information affects global warming and the resulting impact it has on us, our friends and family, and humanity in general. 

To help us in this process, we need a clear understanding of global warming, including what’s causing it and what are its consequences. In other words, it requires an understanding of the entire picture of global warming. This allows us to fit these information pieces in their proper place to see how they impact the entire picture.  It is similar to fitting the pieces of a puzzle together so we can clearly see the picture the puzzle creates.

The purpose of this report is to provide an overview of the causes leading up to and the consequences resulting from the warming of the earth. As shown in Figure 1 there are six phases in this process. It starts with us (human activity) and ends with us (impact on humans).  It begs the question, “What are we doing to ourselves”?

Causes of Global warming and its consequesnces

The report below helps us understand these stages and how they are linked.  Only by understanding the total picture can we make reasonable decisions of how to mitigate the effects of global warming. 

Human Activity

The industrial revolution was a period of transition from producing things by hand to producing them by machine.  The machines were steam powered and required large amounts of coal to heat and convert water into steam.  This period, spanning the last half of the 18th century and first half of the 19th century and was a major step in the creation of our modern economy.  But a negative aspect of the industrial revolution was the carbon emissions from burning coal.

The early 20th century was marked by the transportation revolution where the mobility of people and products was greatly expanded through the use of crude oil to power the internal combustion engines. This advancement was another great step forward for our economy but also created carbon emissions.

The expanded use of fossil fuels such as coal, crude oil and natural gas has been a major factor in creating the standard of living we enjoy today.  But releasing carbon into the atmosphere that has been sequestered deep in the earth for millions of years is negatively impacting our world.

Greenhouse Gas Emissions (GHG)

Energy from the sun heats the earth’s surface.  Light rays hitting the earth’s surface are either reflected or absorbed.  Absorbed light is converted into heat. Some of the heat is absorbed by the earth’s surface, some is conducted to the atmosphere, and some is emitted back upward as infrared radiation (heat), which either finds its way into space or is absorbed by greenhouse gases in the atmosphere. Greenhouse gases absorb this heat and slowly radiates it back into the atmosphere. The amount of warming is related to the amount and type of greenhouse gases in the atmosphere. A simplified diagram of this process is shown in Figure 2.

The greenhouse effect diagram

Carbon dioxide makes up 76 percent of global greenhouse gas emissions as shown in Figure 3. It has an atmospheric life of several decades.  Methane, a major component of natural gas, is another greenhouse gas.  Methane is a potent greenhouse gas.  Other atmospheric greenhouse gases include nitrous oxide and chlorofluorocarbons.

Global greenhouse gas emissions

Water vapor is the most prevalent greenhouse gas but is not included in the gases in Figure 3 because it moves in and out of the atmosphere rapidly. The greenhouse gases that impact the gradual warming of the earth’s surface are those listed above because they stay in the atmosphere for a long period of time. But water vapor is important. As the atmosphere warms from the impact of the long-life greenhouse gases, it can hold more water vapor and subsequently increase the warming of the atmosphere even more. 

GHG Atmospheric Buildup

A common misunderstanding is that a reduction of greenhouse gas emissions will result in a decrease in the level of atmospheric greenhouse gases. However, due to the long life of greenhouse gases in the atmosphere, even declining emissions will continue to build up greenhouse gas levels in the atmosphere.

To understand the relationship between greenhouse gas emissions and the atmospheric concentration of greenhouse gases, think of the gas emissions as a bathtub water faucet and the atmosphere as the bathtub.  Gas emissions coming into the bathtub through the faucet increase the amount of gases in the bathtub.  As long as gas emissions come into the tub, the amount of gases in the tub will increase.
However, there is a small drain in the bathtub.  This is in the form of greenhouse gases absorbed by the earth and oceans (called sinks).  But the amount of gases pouring in through the faucet overwhelm the amount escaping through the drain. Reducing the amount of gases coming in through the faucet will slow the buildup of gases in the tub.  But as long as more gas is entering the tub than leaving the tub, the amount of gas in the tub will increase.   Only by stopping the gas emissions coming into the bathtub can we be assured that the buildup of greenhouse gases in the bathtub will stop. 

The buildup of atmospheric carbon dioxide (the most prevalent long-term greenhouse gas) is shown in Figure 4.  In 1960 the atmospheric concentration was less than 320 parts per million by volume (ppmv).  Currently, the concentration is about 400 ppmv, an increase of over 80 ppmv in 55 years.  The atmosphere now contains more carbon dioxide than at any time in the last 420,000 years and possibly the last 20 million years.  With strong economic growth and no limits on emissions, atmospheric concentration could reach 600 ppmv by 2050. Even with severe limits on carbon dioxide emissions, atmospheric concentration is expected to be at least 450 by 2050. 

Atmospheric carbon dioxide

A portion of atmospheric carbon dioxide has a natural cycle.  Large amounts of carbon pass back and forth between the atmosphere and the earth’s surface. For example, plants (e.g. crops and trees) grow through photosynthesis where carbon dioxide is taken in and separated into carbon and oxygen.  The carbon is used to build the plant and the oxygen is emitted back into the atmosphere.  When the plant dies and deteriorates, the carbon combines with atmospheric oxygen in the decomposition process to re-create carbon dioxide.  The wavy line in Figure 4is the cycle of annual plants in the northern hemisphere that take in carbon dioxide during the spring and summer and release it in the fall and winter.  These cycles do not impact the long-term uptrend in atmospheric carbon dioxide.

Global Warming

Global warming is the increase in the average temperature of Earth's near-surface air and oceans. As shown in Figure 5, there has been an overall upward trend in global temperature over the last 135 years, especially the last 45 years.  2015 is expected to be the warmest on record with 2011-2015 the warmest five year period on record. 2015 is expected to reach the 1 degree Celsius (1.8 degrees Fahrenheit) increase in global temperatures since the pre-industrial period.

Global temperatures

Is the global increase in temperature due to natural factors or is it man-made. There are natural drivers that heat and cool the earth. Two major natural drivers are the sun and volcanoes.  Solar energy heats the planet’s surface and atmosphere. Sunspots correlate to the changes in intensity of solar radiation reaching the earth. Sunspot activity goes through cycles and can both warm and cool the earth. Volcanic activity temporarily cools the earth.

Natural drivers alone cannot explain the rise in global temperature since the 1970s as shown in Figure 6.  Only when the anthropogenic (man-made) drivers and natural drivers are combined can the temperature rise be explained. 

Human and natural influenes on climate

Although the earth has warmed and will continue to warm, the temperature increase is not distributed evenly. For example, the arctic is warming twice as fast as the earth as a whole.  Also, the warming over land tends to be greater than the warming over oceans. The temperature increase that has occurred in the U.S. since 1900 is shown in Figure 7. The warming tends to be concentrated in certain parts of the country. Temperature has risen the most in the Southwest, New England and Alaska. 

Rate of temperature chane in the U.S.

Global warming will continue into the future.  The amount of warming will be determined by the amount of greenhouse gas emissions.  Figure 8 shows projections of warming from now until 2100 under four scenarios of greenhouse gas emissions.  The lines represent the average temperature under each scenario and the bars represent the range of possible outcomes at 2100.   The blue line indicates just a modest increase in temperature if emissions are severely restricted. Conversely, the red line shows a substantial increase in warming if emissions increase without restriction.  The orange and light blue lines represent scenarios of modest emissions restrictions.  Note that three of the scenarios represent more than a two degrees Celsius (3.6 degrees Fahrenheit) increase from pre-1970 temperatures.  Limiting warming to two degrees Celsius is the threshold at which warming is believed to create dangerous climate change.

Global temperature projections

Climate Change

As the earth warms it drives changes in the earth’s climate.  Expected changes in climate of the United States climate due to the warming of the earth are discussed below.

People often have difficulty understanding the relationship between climate and weather. Climate is a long-term phenomenon where weather is current.  If you are a baseball fan, think of a batter’s RBI as climate.  It is a record over the baseball season of the batters record of driving in runs.  If the batter has a hot streak the RBI will trend upward.  A batting slump will drive the RBI downward. By contrast, think of the batter being up-to-bat as weather.  Either the batter hits the ball into the field of play or strikes out.

Increase average temperature – Figure 9 shows projections of changes in the U.S. temperature by mid-century and end-of-century under scenarios of high and low greenhouse gas emissions. The maps show temperature impacts for various parts of the U.S under the different scenarios and time periods. The brackets on the thermometers represent the likely range of projections, though lower or higher outcomes are possible.

U.S. Temperature Projections

Influence the patterns and amounts of precipitation – Projected changes in U.S. precipitation patterns by the end of the century under a high emissions scenario are shown in Figure 10.  Confidence in the projected changes is highest in the areas marked with diagonal lines.  Changes in white are projected to be similar to natural variation. In spring and summer, northern areas of the United States are likely to get wetter and southern areas drier.

U.S. Precipitation Projections

Reduce ice, snow cover and permafrost -- Every two degrees Fahrenheit of warming results in about a 25 percent decrease in the area covered by Arctic sea ice at the end of summer. The coastal sections of the Greenland and Antarctic ice sheets are expected to continue to melt or slide into the ocean. Glaciers are expected to continue to decrease in size. Northern Hemisphere snow cover is expected to decrease by approximately 15 percent by 2100.  The snow season is projected to continue to shorten. Permafrost is expected to continue to thaw in northern latitudes.

Raise sea level – Sea level rise is shown in Figure 11.  The orange line at right shows the projected range of expected sea level rise by 2100.  The projected rise of one to four feet is a combination of melted snow and ice and warming of the oceans (as water warms it expands). Snow and ice already in the water do not raise sea level as they melt (e.g. icebergs). Snow and ice over land do raise sea level as they melt.  Examples are snow and ice over Greenland and Antarctica.  

Project seal level rise

Increase the acidity of the oceans -- As atmospheric carbon dioxide dissolves in the oceans, the oceans become acidic. As the acidity of the oceans increases, the availability of calcium carbonate declines.  Calcium carbonate is an important building block for sea life with shells and skeletons. Ocean acidity is already a problem and the level of acidity is expected to continue to increase in the future as the level of atmospheric carbon dioxide rises. 

Increase the frequency, intensity, and/or duration of extreme events – Weather events with heavy precipitation will likely increase. Heavy downpours that currently occur about once every 20 years are projected to occur two to five times more often by 2100. More precipitation will fall as rain rather than snow. The intensity of Atlantic hurricanes is likely to increase as the ocean warms. The number of strong hurricanes is also expected to increase. Rainfall rates in hurricanes are expected to increase. Cold-season storm tracks are expected to shift northward with the strongest cold-season storms becoming stronger and more frequent.

Impact on Humans

No one will be exempt from the impacts of climate change.  The climate in which we live is our home. We are well suited to live in our climate home. However, as global warming increases, the home in which we and our children live will change. Even, if by chance, the climate in which some of us live does not change, the climate in most of the rest of the world will change and impact us and our children. The more the earth warms, the more the climate will change and the greater will be the negative impact on our lives.

The warming earth and the resulting changes in climate will have a variety of negative impacts on humans.  The impacts will be on basic needs such as food, water, health, shelter and security. Although climate change is a global issue, the impact will not be felt equally around the earth. Some countries will suffer more than others.  Some countries may actually benefit. Groups of people especially vulnerable to the impacts of climate change include the elderly, children and low-income communities.

Impacts on Agriculture and Food – Climate change will have a significant impact on food production. Droughts, floods, heat and other stressors will negatively impact crop and livestock production.  Areas with limited water supply may suffer from even less water.  Although crops grown in the mid to high latitudes may benefit, those at lower latitudes will suffer.   The resulting food shortages could increase the risk of a humanitarian crises in various parts of the world.

Impacts on Cities -- Fifteen of the world's twenty megacities are vulnerable to sea level rise and increased coastal storm surges.  These changes threaten the lives and property of millions of people.

Impacts on Human Health -- Climate can play a significant role in people’s health. Temperature increases result in more frequent and severe heat stress, leading to more heat-related illnesses. Climate changes can influence infectious diseases. Groups of people in low-income countries are especially at-risk due to adverse health effects from climate change.

Impacts on Poverty -- About one quarter of the people of the developing world live in extreme poverty. These people are the most vulnerable to climate change as they already live on the edge and have limited ability to cope with changing climate. 

Impacts on National Security -- Floods, droughts, hurricanes and other extreme weather events will negatively impact groups of people and lead to conflicts resulting in the migration of people within and between countries. This disruption may lead to political instability and conflicts that result in threats to the U.S.

What Does the Future Hold?

Apparent from the information above, the impact of global warming and climate change starts with human activity and ends with the impact on humans.  The solution is obvious.  Move away from fossil fuels that increase the level of atmospheric greenhouse gases.  However, humans don’t tend to address a problem until it has become severe. 

Long time lag -- There is a long time lag (decades) between harmful human activities and the resulting negative impact on humans.  So, it is difficult to convince ourselves to take corrective action when the negative consequences lie far in the future.  Viewed from another perspective, once the negative effects become severe, it may be too late to take corrective actions.

Feedback Loops – An important aspect of global warming is the feedback loops in the system.  Some of these have the ability to negatively impact our ability to control global warming. 

An example involves the melting of arctic snow and ice cover.  When the sun’s rays hit snow and ice, only a small amount of the sun’s rays are absorbed as heat.  Most of the rays are reflected back in the sky. However, if snow and ice do not form due to global warming, the sun’s rays hit open water where much of the resulting heat is absorbed by the water. As more snow and ice melt, more water is exposted to the suns rays, which results in the absorption of more heat by the oceans.  A feedback loop is formed that takes on a life of its own.   

Another example involves the huge amount of carbon locked-up in the permafrost of the arctic.  As the earth warms, the permafrost begins to melt which releases the lock-up carbon into the atmosphere primarily in the form of methane (CH4), a very powerful greenhouse gas.  The increased level of methane leads to more warming which melts more permafrost and releases more carbon to make more methane in the atmosphere. Once again a feedback loop is formed that takes on a life of its own.

Feedback loops like these and others may become drivers of global warming that are independent of what we do to restrict fossil fuels.  The warming of the earth and its impact on climate may become beyond our ability to stop.  The first stage “Human Activity” in Figure 1 at the beginning of this report could be replaced with “Human Activity and Uncontrollable Feedback Loops” as shown in Figure 12.

Drivers of global warming and its consequences