“GLOBAL WARMING VS. CLIMATE CHANGE”
The Important Differences Between "Climate Change" and "Global Warming''
Many people in the media (and elsewhere) use the terms "climate change" and "global warming" interchangeably, as if they were the same thing. But there are differences between the meanings of the two terms. Getting a better handle on the definitions of and differences between "global warming" and "climate change" will help us understand why the threat caused by continued warming of the planet is so serious.
GLOBAL WARMING AND CLIMATE CHANGE
Definitions
Global Warming — An overall warming of the planet, based on average
temperature over the entire surface.
Climate Change — Changes in regional climate characteristics, including temperature, humidity, rainfall, wind, and severe weather events.
CLIMATE CHANGE VS. GLOBAL WARMING
Global Warming — The Heat is On
Planet Earth's current warming trend is based largely on natural warming and cooling cycles that have been
happening for eons; as well as human-caused additions to greenhouse gases, which are boosting the atmosphere's ability to trap heat in the biosphere. Minor factors like an overall increase in the sun's solar intensity play a smaller role.
While greenhouse gases are an essential component of a livable planet—they're what keep Earth from being a lifeless ball of ice—humans are causing greenhouse gas levels to increase so quickly that it's causing the average global temperature to rise much faster than it would naturally.
This warming is predicted to lead to a variety of negative effects, including:
- Melting (and possible disappearance) of glaciers and mountain snow caps that feed the world's rivers and supply a large portion of the fresh water used for drinking and irrigation.
- A rise in sea levels due to the melting of the land-based ice sheets in Greenland and Antarctica, with many islands and coastal areas ending up more exposed to storm damage or even underwater.
- Increases in vector-borne infectious diseases like malaria and Lyme Disease.
- Large numbers of extinctions of higher-level species due to their inability to adapt to rapidly changing climate and habitat conditions.
The first two of these effects are mostly related to increasing average temperatures. Items 3-6 are related to heat too, but also playing a role are non-temperature factors—i.e. "climate-change factors."
DIFFERENCES BETWEEN GLOBAL WARMING AND CLIMATE CHANGE
Climate Change—Beyond Withering Weather
Climate change is about much more than how warm or cool our temperatures are. Whereas "global warming" refers to increasing global temperatures, "climate change" refers to regional conditions. Climate is defined by a number of factors, including:
- Average regional temperature as well as day/night temperature patterns and seasonal temperature patterns.
- Humidity.
- Precipitation (average amounts and seasonal patterns).
- Average amount of sunshine and level of cloudiness.
- Air pressure and winds.
- Storm events (type, average number per year, and seasonal patterns).
To a great extent, this is what we think of as "weather." Indeed, weather patterns are predicted to change in response to global warming:
- some areas will become drier, some will become wetter;
- many areas will experience an increase in severe weather events like killer heat waves, hurricanes, flood-level rains, and hail storms.
It's tempting to think that al
l of these changes to the world's climate regions will average out over time and geography and things will be fine. In fact, colder climates like Canada may even see improved agricultural yields as their seasonal temperatures rise. But overall, humanity has made a huge investment in "things as they are now, where they are now." Gone are the days of millennia ago when an unfavorable change in climate might cause a village to pack up their relatively few belongings and move to a better area. We have massive societal and industrial infrastructure in place, and it cannot be easily moved. Climate-change effects will generally not be geographically escapable in the time-frame over which they happen, at least not for the majority of humans and species.
How Does Your Garden Grow ... In a Desert?
Beyond mere "weather," we can also think of a region's climate as a place in which things live—a la, "a hospitable climate." Therein lies the real danger of global warming—climate change will affect the success or failure of how plants and animals live in a given geographic area, including food crops.
We think of the Central Valley of California as a lush, agriculturally productive landscape, but central California's climate is actually quite dry. Without intensive use of irrigation, the land would not produce the volume or variety of food it does now. So, what if increasing temperatures cause less snow pack to accumulate in the mountains each year, leading to lower river flows and less water available for irrigation in California's agricultural areas? What if changes in rainfall patterns make central California's
climate even drier? How much would crop output fall?
This is just one example of how global warming could lead to a regional climate change that would cause a big difference in local economics and the national food supply.
Climate Change – Currently Very Uncool
Even though the main threat right now is warming planetary temperatures, climate change can also mean global cooling. The last Ice Age was part of a globally cool period and it featured some rather severe "climate change" characteristics.
| It's worth remembering that global warming is based on an in creasing average global temperature. Some parts of the planet (such as the Arctic) are getting warmer much faster than other areas. It's even possible that some regions could actually experience regional cooling at the same time the planet as a whole is experiencing global warming. Here's how. The "thermohalinecirculation" in the world's oceans is part of the planet's temperature regulation system. It can warm or cool regional climates to make their average temperatures different that they would be normally based on their latitude. The most notable example of this is how the Gulf Stream brings warm water up from the tropics to make Europe much warmer than it would be naturally. This part of the thermohaline circulation is dependent on regular additions of fresh water from melting Arctic ice (which is replaced every year through additional snowfall). If the flow of fresh Arctic water decreases enough, it could slow or even stop the thermohaline circulation, leading to cooler temperatures in Europe—even at the same time other areas are experiencing severe temperature increases. |
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Global Warming vs. The Next Ice Age
Those who are skeptical about the threat posed by global warming often point to the fact that a few decades ago, some scientists were warning us that a new ice age could wipe us all out. After all, during the last Ice Age—which ended 10,000 years ago or so—much of North America was covered with an impenetrable sheet of ice. A repeat of that would indeed be big trouble.
Because of scientists' previous warnings that a new Ice Age might be in our future, global warming skeptics sometimes say that scientists can't make up their mind—first it's global cooling, then it's global warming. But let's remember three things:
(1) Back in the 1970s, at the same time a few scientists were warning of a possible new Ice Age, other scientists were already warning about the emerging evidence of global warming.
(2) The scientific community is now overwhelmingly in agreement that there is a threat from global warming and that there is no threat of another Ice Age, at least not in the timeframe that counts.
(3) The amount of temperature increase predicted from now to the end of the century is roughly the same as the temperature difference between now and the last Ice Age. (Yes, really!) It would be foolish to think that an equivalent but opposite move in temperature might be a good thing.
Global Warming vs. The Next Ice Age
Those who are skeptical about the threat posed by global warming often point to the fact that a few decades ago, some scientists were warning us that a new ice age could wipe us all out. After all, during the last Ice Age—which ended 10,000 years ago or so—much of North America was covered with an impenetrable sheet of ice. A repeat of that would indeed be big trouble.
Because of scientists' previous warnings that a new Ice Age might be in our future, global warming skeptics sometimes say that scientists can't make up their mind—first it's global cooling, then it's global warming. But let's remember three things:
(1) Back in the 1970s, at the same time a few scientists were warning of a possible new Ice Age, other scientists were already warning about the emerging evidence of global warming.
(2) The scientific community is now overwhelmingly in agreement that there is a threat from global warming and that there is no threat of another Ice Age, at least not in the timeframe that counts.
(3) The amount of temperature increase predicted from now to the end of the century is roughly the same as the temperature difference between now and the last Ice Age. (Yes, really!) It would be foolish to think that an equivalent but opposite move in temperature might be a good thing.
Wrap-Up
There are important differences between global warming and climate change, but the two are closely intertwined in determining the climate futures for the regions where we live. Predictions of regional impacts are beginning to emerge from climate models. There are regions that will get some benefits, but most of the predicted effects around the world are bad—bad enough that we need to quickly start fixing our greenhouse gas emissions.
There are solutions, but most leaders today are offering only low-impact solutions that will not truly solve the problem. We need to be talking about how to cut greenhouse gas emiss
ions by 50%-80% over the next few decades, not dithering over minimalist efforts like how to get back to 1990 levels by the year 2020.
Some leaders just offer excuses about why no action is possible, citing "the economy" as a reason to continue ignoring the problem. But a report from the British government about the economic damage that will be caused by inaction on climate change makes it clear that continued delay is unwise, even from an economic standpoint.
Many of the actions necessary to solve the global warming problem must be attacked at the national and international levels. But in the US, states and cities are thus far in the lead on implementing solutions. In the end, total success will have to be built on our actions as individuals (regardless of country), from energy conservation to vehicle choices to what we demand of our leaders. You too can be part of these global warming solutions!
Causes of Global Warming
Photograph by Peter Essick
What Causes Global Warming?
Scientists have spent decades figuring out what is causing global warming. They've looked at the natural cycles and events that are known to influence climate. But the amount and pattern of warming that's been measured can't be explained by these factors alone. The only way to explain the pattern is to include the effect of greenhouse gases (GHGs) emitted by humans.
To bring all this in format
ion together, the United Nations formed a group of scientists called the International Panel on Climate Change, or IPCC. The IPCC meets every few years to review the latest scientific findings and write a report summarizing all that is known about global warming. Each report represents a consensus, or agreement, among hundreds of leading scientists.
One of the first things scientists learned is that there are several greenhouse gases responsible for warming, and humans emit them in a variety of ways. Most come from the combustion of fossil fuels in cars, factories and electricity production. The gas responsible for the most warming is carbon dioxide, also called CO2. Other contributors include methane released from landfills and agriculture (especially from the digestive systems of grazing animals), nitrous oxide fro
m fertilizers, gases used for refrigeration and industrial processes, and the loss of forests that would otherwise store CO2.
Different greenhouse gases
s have very different heat-trapping abilities. Some of them can even trap more heat than CO2. A molecule of methane
produces more than 20 times the warming of a molecule of CO2. Nitrous oxide is 300 times more powerful than CO2. Other gases, such as chlorofluorocarbons (which have been banned in much of the world because they also degrade the ozone layer), have heat-trapping potential thousands of times greater than CO2. But because their concentrations are much lower than CO2, none of these gases adds as much warmth to the atmosphere as CO2 does.
In order to understand the effects of all the gases together, scientists tend to talk about all greenhouse gases in terms
of the equivalent amount of CO2. Since 1990, yearly emissions have gone up by about 6 billion metric tons of "carbon dioxide equivalent" worldwide, more than a 20% increase.
Causes of climate change
The earth's climate is dynamic and always changing through a natural cycle. What the world is more worried about is that the changes that are occurring today have been speeded up because of man's activities. These changes are being studied by scientists all over the world who are finding evidence from tree rings, pollen samples, ice cores, and sea sediments. The causes of climate change can be divided into two categories - those that are due to natural causes and those that are created by man.
Natural causes
There are a number of natural factors responsible for climate change. Some of the more prominent ones are continental drift, volcanoes, ocean currents, the earth's tilt, and comets and meteorites. Let's look at them in a little detail.
You may have noticed something peculiar about South America and Africa on a map of the world - don't they seem to fit into each other like pieces in a jigsaw puzzle?
About 200 million years ago they were joined together! Scientists believe that back then, the earth was not as we see it today, but the continents were all part of one large landmass. Proof of this comes from the similarity between plant and animal fossils and broad belts of rocks found on the eastern coastline of South America and western coastline of Africa, which are now widely separated by the Atlantic Ocean. The discovery of fossils of tropical plants (in the form of coal deposits) in Antarctica has led to the conclusion that this frozen land at some time in the past, must have been situated closer to the equator, where the climate was tropical, with swamps and plenty of lush vegetation.
The continents that we are familiar with today were formed when the landmass began gradually drifting apart, millions of years back. This drift also had an impact on the climate because it changed the physical features of the landmass, their position and the position of water bodies. The separation of the landmasses changed the flow of ocean currents and winds, which affected the climate. This drift of the continents continues even today; the Himalayan range is rising by about 1 mm (millimeter) every year because the Indian land mass is moving towards the Asian land mass, slowly but steadily.
When a volcano erupts it throws out large volumes of sulfur dioxide (SO2), water vapor, dust, and ash into the atmosphere. Although the volcanic activity may last only a few days, yet the large volumes of gases and ash can influence climatic patterns for years. Millions of tonnes of sulfur dioxide gas can reach the upper levels of the atmosphere (called the stratosphere) from a major eruption. The gases and dust particles partially block the incoming rays of the sun, leading to cooling. Sulfur dioxide combines with water to form tiny droplets of sulfuric acid. These droplets are so small that many of them can stay aloft for several years. They are efficient reflectors of sunlight, and screen the ground from some of the energy that it would ordinarily receive from the sun. Winds in the upper levels of the atmosphere, called the stratosphere, carry the aerosols rapidly around the globe in either an easterly or westerly direction. Movement of aerosols north and south is always much slower. This should give you some idea of the ways by which cooling can be brought about for a few years after a major volcanic eruption.
Mount Pinatobu, in the Philippine islands erupted in April 1991 emitting thousands of tonnes of gases into the atmosphere. Volcanic eruptions of this magnitude can reduce the amount of solar radiation reaching the Earth's surface, lowering temperatures in the lower levels of the atmosphere (called the troposphere), and changing atmospheric circulation patterns. The extent to which this occurs is an ongoing debate.
Another striking example was in the year 1816, often referred to as "the year without a summer." Significant weather-related disruptions occurred in New England and in Western Europe with killing summer frosts in the United States and Canada. These strange phenomena were attributed to a major eruption of the Tambora volcano in Indonesia, in 1815.
The earth makes one full orbit around the sun each year. It is tilted at an angle of 23.5° to the perpendicular plane of its orbital path. For one half of the year when it is summer, the northern hemisphere tilts towards the sun. In the other half when it is winter, the earth is tilted away from the sun. If there was no tilt we would not have experienced seasons. Changes in the tilt of the earth can affect the severity of the seasons - more tilt means warmer summers and colder winters; less tilt means cooler summers and milder winters.
The Earth's orbit is somewhat elliptical, which means that the distance between the earth and the Sun varies over the course of a year. We usually think of the earth's axis as being fixed, after all, it always seems to point toward Polaris (also known as the Pole Star and the North Star). Actually, it is not quite constant: the axis does move, at the rate of a little more than a half-degree each century. So Polaris has not always been, and will not always be, the star pointing to the North. When the pyramids were built, around 2500 BC, the pole was near the star Thuban (Alpha Draconis). This gradual change in the direction of the earth's axis, called precession is responsible for changes in the climate.
The oceans are a major component of the climate system. They cover about 71% of the Earth and absorb about twice as much of the sun's radiation as the atmosphere or the land surface. Ocean currents move vast amounts of heat across the planet - roughly the same amount as the atmosphere does. But the oceans are surrounded by land masses, so heat transport through the water is through channels.
Winds push horizontally against the sea surface and drive ocean current patterns.
Certain parts of the world are influenced by ocean currents more than others. The coast of Peru and other adjoining regions are directly influenced by the Humboldt current that flows along the coastline of Peru. The El Niño event in the Pacific Ocean can affect climatic conditions all over the world.
Another region that is strongly influenced by ocean currents is the North Atlantic. If we compare places at the same latitude in Europe and North America the effect is immediately obvious. Take a closer look at this example - some parts of coastal Norway have an average temperature of -2°C in January and 14°C in July; while places at the same latitude on the Pacific coast of Alaska are far colder: -15°C in January and only 10°C in July. The warm current along the Norwegian coast keeps much of the Greenland-Norwegian Sea free of ice even in winter. The rest of the Arctic Ocean, even though it is much further south, remains frozen.
Ocean currents have been known to change direction or slow down. Much of the heat that escapes from the oceans is in the form of water vapour, the most abundant greenhouse gas on Earth. Yet, water vapor also contributes to the formation of clouds, which shade the surface and have a net cooling effect.
Any or all of these phenomena can have an impact on the climate, as is believed to have happened at the end of the last Ice Age, about 14,000 years ago.
Human causes
The Industrial Revolution in the 19th century saw the large-scale use of fossil fuels for industrial activities. These industries created jobs and over the years, people moved from rural areas to the cities. This trend is continuing even today. More and more land that was covered with vegetation has been cleared to make way for houses. Natural resources are being used extensively for construction, industries, transport, and consumption. Consumerism (our increasing want for material things) has increased by leaps and bounds, creating mountains of waste. Also, our population has increased to an incredible extent.
All this has contributed to a rise in greenhouse gases in the atmosphere. Fossil fuels such as oil, coal and natural gas supply most of the energy needed to run vehicles, generate electricity for industries, households, etc. The energy sector is responsible for about ¾ of the carbon dioxide emissions, 1/5 of the methane emissions and a large quantity of nitrous oxide. It also produces nitrogen oxides (NOx) and carbon monoxide (CO) which are not greenhouse gases but do have an influence on the chemical cycles in the atmosphere that produce or destroy greenhouse gases.
Carbon dioxide is undoubtedly, the most important greenhouse gas in the atmosphere. Changes in land use pattern, deforestation, land clearing, agriculture, and other activities have all led to a rise in the emission of carbon dioxide.
Methane is another important greenhouse gas in the atmosphere. About ¼ of all methane emissions are said to come from domesticated animals such as dairy cows, goats, pigs, buffaloes, camels, horses, and sheep. These animals produce methane during the cud-chewing process. Methane is also released from rice or paddy fields that are flooded during the sowing and maturing periods. When soil is covered with water it becomes anaerobic or lacking in oxygen. Under such conditions, methane-producing bacteria and other organisms decompose organic matter in the soil to form methane. Nearly 90% of the paddy-growing area in the world is found in Asia, as rice is the staple food there. China and India, between them, have 80-90% of the world's rice-growing areas.
Methane is also emitted from landfills and other waste dumps. If the waste is put into an incinerator or burnt in the open, carbon dioxide is emitted. Methane is also emitted during the process of oil drilling, coal mining and also from leaking gas pipelines (due to accidents and poor maintenance of sites).
A large amount of nitrous oxide emission has been attributed to fertilizer application. This in turn depends on the type of fertilizer that is used, how and when it is used and the methods of tilling that are followed. Contributions are also made by leguminous plants, such as beans and pulses that add nitrogen to the soil.
All of us in our daily lives contribute our bit to this change in the climate. Give these points a good, serious thought:
- Electricity is the main source of power in urban areas. All our gadgets run on electricity generated mainly from thermal power plants. These thermal power plants are run on fossil fuels (mostly coal) and are responsible for the emission of huge amounts of greenhouse gases and other pollutants.
- Cars, buses, and trucks are the principal ways by which goods and people are transported in most of our cities. These are run mainly on petrol or diesel, both fossil fuels.
- We generate large quantities of waste in the form of plastics that remain in the environment for many years and cause damage.
- We use a huge quantity of paper in our work at schools and in offices. Have we ever thought about the number of trees that we use in a day?
- Timber is used in large quantities for construction of houses, which means that large areas of forest have to be cut down.
- A growing population has meant more and more mouths to feed. Because the land area available for agriculture is limited (and in fact, is actually shrinking as a result of ecological degradation!), high-yielding varieties of crop are being grown to increase the agricultural output from a given area of land. However, such high-yielding varieties of crops require large quantities of fertilizers; and more fertilizer means more emissions of nitrous oxide, both from the field into which it is put and the fertilizer industry that makes it. Pollution also results from the run-off of fertilizer into water bodies.
FAQ:
How do we know that humans are the major cause of global warming?
The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) states: it is a greater than a 90 percent certainty that emissions of heat-trapping gases from human activities have caused “most of the observed increase in globally averaged temperatures since the mid-20th century.” We all know that warming—and cooling—has happened in the past, and long before humans were around. Many factors (called “climate drivers”) can influence Earth’s climate—such as changes in the sun’s intensity and volcanic eruptions, as well as heat-trapping gases in the atmosphere.
So how do scientists know that today’s warming is primarily caused by humans putting too much carbon in the atmosphere when we burn coal, oil, and gas or cut down forests?
- There are human fingerprints on carbon overload. When humans burn coal, oil and gas (fossil fuels) to generate electricity or drive our cars, carbon dioxide is released into the atmosphere, where it traps heat. A carbon molecule that comes from fossil fuels and deforestation is “lighter” than the combined signal of those from other sources. As scientists measure the “weight” of carbon in the atmosphere over time they see a clear increase in the lighter molecules from fossil fuel and deforestation sources that correspond closely to the known trend in emissions.
- Natural changes alone can’t explain the temperature changes we’ve seen. For a computer model to accurately project the future climate, scientists must first ensure that it accurately reproduces observed temperature changes. When the models include only recorded natural climate drivers—such as the sun’s intensity—the models cannot accurately reproduce the observed warming of the past half century. When human-induced climate drivers are also included in the models, then they accurately capture recent temperature increases in the atmosphere and in the oceans. [4][5][6] When all the natural and human-induced climate drivers are compared to one another, the dramatic accumulation of carbon from human sources is by far the largest climate change driver over the past half century.
- Lower-level atmosphere—which contains the carbon load—is expanding. The boundary between the lower atmosphere (troposphere) and the higher atmosphere (stratosphere) has shifted upward in recent decades. See the ozone FAQ for a figure illustrating the layers of the atmosphere. [6][7][8]This boundary has likely changed because heat-trapping gases accumulate in the lower atmosphere and that atmospheric layer expands as it heats up (much like warming the air in a balloon). And because less heat is escaping into the higher atmosphere, it is likely cooling. This differential would not occur if the sun was the sole climate driver, as solar changes would warm both atmospheric layers, and certainly would not have warmed one while cooling the other.
Figure 2. Twentieth Century History of Climate Drivers
(Click to image to enlarge) Heat-trapping emissions (greenhouse gases) far outweigh the effects of other drivers acting on Earth’s climate. Source: Hansen et al. 2005, figure adapted by Union of Concerned Scientists.
Why does CO2 get most of the attention when there are so many other heat-trapping gases (greenhouse gases)?
Global warming is primarily a problem of too much carbon dioxide in the atmosphere. This carbon overload is caused mainly when we burn fossil fuels like coal, oil and gas or cut down and burn forests. There are many heat-trapping gases (from methane to water vapor), but CO2 puts us at the greatest risk of irreversible changes if it continues to accumulate unabated in the atmosphere. There are two key reasons why.
CO2 has caused most of the warming and its influence is expected to continue. CO2, more than any other climate driver, has contributed the most to climate change between 1750 and 2005.[1, 2, 3] The Intergovernmental Panel on Climate Change (IPCC) issued a global climate assessment in 2007 that compared the relative influence exerted by key heat-trapping gases, tiny particles known as aerosols, and land use change of human origin on our climate between 1750 and 2005.[3] By measuring the abundance of heat-trapping gases in ice cores, the atmosphere, and other climate drivers along with models, the IPCC calculated the “radiative forcing” (RF) of each climate driver—in other words, the net increase (or decrease) in the amount of energy reaching Earth’s surface attributable to that climate driver. Positive RF values represent average surface warming and negative values represent average surface cooling. CO2 has the highest positive RF (see Figure 1) of all the human-influenced climate drivers compared by the IPCC. Other gases have more potent heat-trapping ability molecule per molecule than CO2 (e.g. methane), but are simply far less abundant in the atmosphere and being added more slowly.
Figure 1. How Does CO2 Compare To Other Climate Drivers?
What is the latest climate science?
Major developments in climate change science have been reported since the publication of the comprehensive 2007 Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC).[1] Recent publications indicate that the consequences of climate change are already occurring at a faster pace and are of greater magnitude than the climate models used by the IPCC projected. A few of the most compelling findings are summarized below.
More CO2 Remains in the Atmosphere
Human activities have pumped excessive amounts of carbon dioxide (CO2) into the atmosphere. Natural processes that absorb CO2 cannot keep up. As the ocean absorbs carbon dioxide, it becomes more acidic. This combined with increasing ocean temperatures, diminishes its ability to continue absorbing CO2. As a result, more CO2 stays in the atmosphere. In 1960, a metric ton (1,000 kilograms; ~2,205 pounds) of CO2 emissions resulted in around 400 kilograms (~881 pounds) of CO2 remaining in the atmosphere (Figure 1). In 2006, a metric ton of CO2 emissions results in around 450 kilograms (~992 pounds) remaining in the atmosphere.[2] Hence a ton of CO2 emissions today results in more heat-trapping capacity in the atmosphere than the same ton emitted decades ago.
Figure 1. Today’s Ton Is Worse Than a Ton Emitted Decades Ago
The natural processes that have helped clean up the excess CO2 pumped into the atmosphere by human activities have not been able to keep up at the same rate.
Does air pollution—specifically particulate matter (aerosols)—affect global warming?
Air pollution occurs when the air contains gases, dust, fumes or odor in harmful amounts—aerosols are a subset of air pollution that refers to the tiny particles suspended everywhere in our atmosphere. These particles can be both solid and liquid and are collectively referred to as ‘atmospheric aerosol particles’ [1]. Most are produced by natural processes such as erupting volcanoes, and some are from human industrial and agricultural activities (see Figure 1). Those particles in the lowest layer of the atmosphere, where our weather occurs, usually stay relatively close to the source of emissions and remain in the atmosphere only a few days to a week before they fall to the ground or are rained out; those higher up in the atmosphere travel farther and may linger in the atmosphere for a few years.
Light-colored aerosol particles can reflect incoming energy from the sun (heat) in cloud-free air and dark particles can absorb it. Aerosols can modify how much energy clouds reflect and they can change atmospheric circulation patterns—in short, aerosols can modify our climate [2].
Several climate engineering (so-called ‘geoengineering’) strategies for reducing global warming propose using atmospheric aerosol particles to reflect the sun’s energy away from Earth. Because aerosol particles do not stay in the atmosphere for very long—and global warming gases stay in the atmosphere for decades to centuries—accumulated heat-trapping gases will overpower any temporary cooling due to short-lived aerosol particles.
Figure 1. Small Particles (Aerosols) in the Atmosphere
Small particles suspended in the Earth’s atmosphere (aerosols) include fine aerosols such as pollution and smoke (red) and coarse aerosols such as dust and sea-salt (green). Image shows aerosol levels on April 13, 2001 as seen by a NASA satellite. Source: NASA
How does the sun affect our climate?
The sun is the source of most of the energy that drives the biological and physical processes in the world around us—in oceans and on land it fuels plant growth that forms the base of the food chain, and in the atmosphere it warms air which drives our weather. The rate of energy coming from the sun changes slightly day to day. Over many millennium in the Earth-Sun orbital relationship can change the geographical distribution of the sun’s energy over the Earth’s surface. It has been suggested that changes in solar output might affect our climate—both directly, by changing the rate of solar heating of the Earth and atmosphere, and indirectly, by changing cloud forming processes.
Over the time-scale of millions of years the change in solar intensity is a critical factor influencing climate (e.g., ice ages). However, changes in solar heating rate over the last century cannot account for the magnitude and distribution of the rise in global mean temperature during that time period and there is no convincing evidence for significant indirect influences on our climate due to twentieth century changes in solar output.
Figure 1. Record of Minimal Variation in Sun’s Energy
(Click to image to enlarge) Figure 1. Two and a half solar cycles of Total Solar Irradiance (TSI), also called 'solar constant'. This composite, compiled by the VIRGO team at the Physikalisch-Meteorologisches Observatorium / World Radiation Center Davos, Switzerland, shows TSI as daily values plotted in different colors for the different originating experiments. The difference between the minima values is also indicated, together with amplitudes of the three cycles. Image courtesy of SOHO consortium a project of international cooperation between ESA and NASA.
Is there a connection between the hole in the ozone layer and global warming?
Ozone (O3) high in the atmosphere absorbs ultraviolet radiation from the sun, thereby protecting living organisms below from this dangerous radiation. The term ‘ozone hole’ refers to recent depletion of this protective layer over Earth's polar regions. People, plants, and animals living under the ozone hole are harmed by the solar radiation now reaching the Earth's surface—where it causes health problems from eye damage to skin cancer.
The ozone hole, however, is not the mechanism of global warming. Ultraviolet radiation represents less than one percent of the energy from the sun—not enough to be the cause of the excess heat from human activities. Global warming is caused primarily from putting too much carbon into the atmosphere when coal, gas, and oil are burned to generate electricity or to run our cars. These gases spread around the planet like a blanket, capturing the solar heat that would otherwise be radiated out into space. (For more detail on the basic mechanism of global warming, see carbon dioxide FAQ.)
Both of these environmental problems do, however, have a common cause—human activities that release gases into and alter the atmosphere. Ozone depletion occurs when chlorofluorocarbons (CFCs)—formerly found in aerosol spray cans and refrigerants—are released into the atmosphere. These gases, through several chemical reactions, cause the ozone molecules to break down, reducing ozone's ultraviolet (UV) radiation-absorbing capacity.
Because our atmosphere is one connected system, it is not surprising that ozone depletion and global warming are related in other ways. For example, evidence suggests that climate change may contribute to thinning of the protective ozone layer.
Figure 1. Seasonal thinning of the ozone layer above Antarctica.
Source: NASA.
What is the best source of scientific information on global warming?
In 1988, the United Nations Environment Programme and the World Meteorological Organization set up the Intergovernmental Panel on Climate Change (IPCC) to examine the most current scientific information on global warming and climate change. More than 1,250 authors and 2,500 scientific experts reviewers from more than 130 countries contributed to the panel's most recent report, Climate Change 2007: The Fourth Assessment Report (the full report will be released in November 2007). These scientists reviewed all the published and peer-reviewed scientific information produced during the previous few years to assess what is known about the global climate, why and how it changes, what it will mean for people and the environment, and what can be done about it.
The IPCC Fourth Assessment Report is the most comprehensive evaluation of global warming that serves as the basis for international climate negotiations. The most up-to-date assessment for the United States was released in June 2009 by 13 federal agencies participating in the U.S. Global Change Research Program (USGCRP). For impacts in American’s back yards the report “Global Climate Change Impacts in the United States” is a valuable resource.
Will responding to global warming be harmful to our economy?
Reducing oil dependence. Strengthening energy security. Creating jobs. Tackling global warming. Addressing air pollution. Improving our health. The United States has many reasons to make the transition to a clean energy economy. What we need is a comprehensive set of smart policies to jump-start this transition without delay and maximize the benefits to our environment and economy. Climate 2030: A National Blueprint for a Clean Energy Economy (“the Blueprint”) answers that need.
To help avoid the most dangerous consequences of climate change, ranging from extreme heat, droughts, and storms to acidifying oceans and rising sea levels, the United States must play a lead role and begin to cut its heat-trapping emissions today—and aim for at least an 80 percent drop from 2005 levels by 2050. Blueprint policies lower U.S. heat-trapping emissions to meet a cap set at 26 percent below 2005 levels in 2020, and 56 percent below 2005 levels in 2030.
The nation achieves these deep cuts in carbon emissions while saving consumers and businesses $465 billion annually by 2030. The Blueprint also builds $1.7 trillion in net cumulative savings between 2010 and 2030. Blueprint policies stimulate significant consumer, business, and government investment in new technologies and measures by 2030. The resulting savings on energy bills from reductions in electricity and fuel use more than offset the costs of these additional investments. The result is net annual savings for households, vehicle owners, businesses, and industries of $255 billion by 2030.
Under the Blueprint, every region of the country stands to save billions. Households and businesses—even in coal-dependent regions—will share in these savings.
What are the options for the vast stores of coal around the world?
If the countries of the world continue burning coal the way they do today, it will be impossible to achieve the reductions in carbon emissions needed to have a reasonable chance of preventing the worst consequences of global warming. Coal-fired power plants represent the United States’ largest source of carbon dioxide (CO2, the main heat-trapping gas building up in our atmosphere and causing climate change).[1,2] While existing coal power technologies are incompatible with climate protection, advanced coal technologies not yet in widespread use may provide an opportunity for the world’s coal reserves to continue playing a role in the energy mix of the future.
Figure 1. Rising Coal Emissions Compared with Needed U.S. Economy-wide Emissions Reductions by 2050
Is global warming already happening?
Yes. The IPCC concluded in its Fourth Assessment Report, that nearly 90 percent of the 29,000 observational data series examined revealed changes consistent with the expected response to global warming, and the observed physical and biological responses have been greatest in the regions that warmed the most.
The kinds of changes already observed that create this consistent picture include the following:
Examples of observed climatic changes
- Increase in global average surface temperature of about 1°F in the 20th century
- Decrease of snow cover and sea ice extent and the retreat of mountain glaciers in the latter half of the 20th century
- Rise in global average sea level and the increase in ocean water temperatures
- Likely increase in average precipitation over the middle and high latitudes of the Northern Hemisphere, and over tropical land areas
- Increase in the frequency of extreme precipitation events in some regions of the world
Examples of observed physical and ecological changes
- Thawing of permafrost
- Lengthening of the growing season in middle and high latitudes
- Poleward and upward shift of plant and animal ranges
- Decline of some plant and animal species
- Earlier flowering of trees
- Earlier emergence of insects
- Earlier egg-laying in birds
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