Q. What are climate change and global warming, and how are they related?
A. Global warming refers to an increase in average global temperatures, which in turn causes climate change.
A. Global warming refers to an increase in average global temperatures, which in turn causes climate change.
Climate change refers to changes in seasonal temperature, precipitation, wind, and humidity for a given area. Climate change can involve cooling or warming.
Temperature readings taken around the world in recent decades, and scientific studies of tree rings, corals, and ice cores, show that average global temperatures have risen since the industrial revolution began, with increases accelerating over the past few decades. The overwhelming consensus among climate scientists is that most of the increase is due to human economic activity, especially the burning of fossil fuels and deforestation. These activities contribute to a build-up in carbon dioxide (CO2) and other gases in Earth’s atmosphere.
Our atmosphere is made up of gases, such as nitrogen, oxygen, and CO2, and water vapor, which act like a “blanket” draped around the planet. Some of these gases—such as CO2, water vapor, and methane—absorb heat, reducing the amount that escapes to space, and increasing global temperatures. This is what is called the “greenhouse effect,” and these gases are often referred to as “greenhouse gases.”
Without this process, the temperature of Earth’s atmosphere would average about 30 degrees Celsius (50 degrees Fahrenheit) colder than it is today, making it difficult for Earth to sustain life as we know it. However, if this blanket were to become too “thick,” with too many gases trapping too much heat, Earth would be uninhabitable. In the atmosphere of Venus, for example, a buildup of carbon dioxide has led to a broiling temperature of 500 degrees Celsius.
Q. What is abrupt climate change?
A. While most climate change generally happens slowly over time, there is evidence that episodes of rapid cooling have occurred in the past, with temperatures falling dramatically over periods of 10 to 20 years. Scientists have found evidence that this has happened at least twice within the past 12,700 years.
Q. What is the scientific consensus on the causes and consequences of climate change?
A. Global warming is real. The global average temperature in 2003 was the third hottest since record keeping began in the late 1800s (1998 was the first, 2002 was second), and the ten warmest years on record have occurred since 1990. The 1990s was the warmest decade in the Northern Hemisphere in the past 1,000 years.
A. Global warming is real. The global average temperature in 2003 was the third hottest since record keeping began in the late 1800s (1998 was the first, 2002 was second), and the ten warmest years on record have occurred since 1990. The 1990s was the warmest decade in the Northern Hemisphere in the past 1,000 years.
What some scientists continue to debate is the extent to which humans are affecting global temperatures and causing climate change. But the majority of scientists who study these issues around the world—including those with the World Meteorological Organization, the Intergovernmental Panel on Climate Change (IPCC), and the U.S. National Academy of Sciences—agree that humans are the main force behind the sharp global warming trend of the past century.
Most scientists agree that the climate changes caused by global warming will never be completely predictable, but that they present serious risks—more extreme temperatures (hot and cold), greater storm intensity and frequency, more frequent droughts and floods, and rising sea levels—that warrant immediate efforts to reduce emissions from fossil fuels.
Q. What role does human activity play in the current global warming trend?
A. A variety of heat trapping—or “greenhouse”—gases collect in Earth’s atmosphere and keep the planet warm enough to sustain life. This occurs through natural processes. For example, humans and animals inhale oxygen and exhale carbon dioxide (CO2). Plants absorb CO2 while growing, but release it as they decompose. The decomposition of cattle manure and peat releases methane, an even stronger, but shorter-lived heat-trapping gas.
A. A variety of heat trapping—or “greenhouse”—gases collect in Earth’s atmosphere and keep the planet warm enough to sustain life. This occurs through natural processes. For example, humans and animals inhale oxygen and exhale carbon dioxide (CO2). Plants absorb CO2 while growing, but release it as they decompose. The decomposition of cattle manure and peat releases methane, an even stronger, but shorter-lived heat-trapping gas.
Human activities also produce greenhouse gases. Carbon dioxide is released when we burn fossil fuels to produce electricity; heat our homes with oil, coal or gas; drive our cars; or switch on our natural gas stoves for cooking. And landfills release methane into the air as our garbage decomposes. Such activities have significantly increased the quantity of several heat-trapping gases in the atmosphere over the past few centuries. For example, carbon dioxide concentrations in the Earth’s atmosphere are 34 percent higher today than they were at the onset of the industrial revolution in 1750—higher than at any time in the last 400,000 years.
Scientists have determined that as atmospheric levels of carbon dioxide have increased, largely due to human activities, the average global temperature has risen significantly. In 2003, the average global temperature was the third highest ever recorded, just slightly below the 1998 and 2002 averages. Scientists predict that average surface temperatures will increase during this century at rates unprecedented in the past 10,000 years.
Q. What role do natural forces play in the current global warming trend?
A. While some scientists continue to believe that global warming could be due to changes in sun spots, natural cycles of warming and cooling, or other factors, most scientists who study this issue now agree that it’s extremely unlikely that these changes in temperature are wholly natural in origin. Instead, they believe the warming we are experiencing today is due to rising concentrations of heat-trapping gases that form a “blanket” around Earth. These gases are put into the atmosphere primarily by human activities—particularly the burning of fossil fuels.
A. While some scientists continue to believe that global warming could be due to changes in sun spots, natural cycles of warming and cooling, or other factors, most scientists who study this issue now agree that it’s extremely unlikely that these changes in temperature are wholly natural in origin. Instead, they believe the warming we are experiencing today is due to rising concentrations of heat-trapping gases that form a “blanket” around Earth. These gases are put into the atmosphere primarily by human activities—particularly the burning of fossil fuels.
Q. Will climate change actually bring benefits to some areas?
A. As a result of global warming and climate change, some regions—such as Siberia—will likely become warmer and more habitable. The growing seasons in some regions will lengthen, as spring arrives earlier and winter frosts set in later.
But betting on the climate is like a game of Russian roulette. Our planet’s climate is a highly complex system that we still don’t fully understand. Likewise, we do not know exactly what the impacts of climate change will be on particular countries or regions. Even an area that welcomes warmer days and lighter jackets might also experience more frequent and intense storm activity, or the arrival of tropical diseases like malaria. At the same time, other places might experience problems like rising sea levels or more extreme heat or cold. And as temperatures rise and become more “comfortable” in some regions of the U.S. or Europe, for example, the number and range of agricultural pests such as insects and diseases will increase, counterbalancing benefits due to warming.
Developing countries will likely be hit hardest as warming continues because they have fewer resources with which to address and adapt to the impacts of climate change. But residents of the United States and other industrial countries will also experience negative consequences, such as increased coastal flooding and more frequent and intense heat waves, droughts, storms, and wildfires as well as the associated economic and health costs.
Most scientists believe that, at least on a global basis, the costs of climate change will far outweigh any benefits that it might bring to a given region.
Q. What are some of the impacts we can expect from climate change?
A. The impacts of climate change will vary from place to place, but we can expect more severe and frequent storms (such as hurricanes and ice storms), heat waves, floods, droughts and wildfires. Warmer temperatures will increase the range of disease-bearing mosquitoes, while also increasing the range and numbers of insects and other agricultural pests, such as weeds. Melting glaciers and expanding sea water (water expands as it warms) will further raise sea level, inundating low-lying islands and flooding coastal areas, while warmer ocean temperatures will kill many if not most of the world’s coral reefs. Such events, in turn, will influence our food supply, our access to clean water, our health, and the economic and social conditions of families and communities around the world.
A. The impacts of climate change will vary from place to place, but we can expect more severe and frequent storms (such as hurricanes and ice storms), heat waves, floods, droughts and wildfires. Warmer temperatures will increase the range of disease-bearing mosquitoes, while also increasing the range and numbers of insects and other agricultural pests, such as weeds. Melting glaciers and expanding sea water (water expands as it warms) will further raise sea level, inundating low-lying islands and flooding coastal areas, while warmer ocean temperatures will kill many if not most of the world’s coral reefs. Such events, in turn, will influence our food supply, our access to clean water, our health, and the economic and social conditions of families and communities around the world.
As ecosystems become further stressed by climate change, species extinction will accelerate. Many of the species lost will be seemingly “insignificant” plants and insects, but we will also lose plants that could cure diseases, and large animals such as polar bears, which rely on winter ice as a platform to hunt for food. Warmer winters could mean reduced snow pack for some regions, reducing water supplies and the output of hydropower dams in the northwestern U.S., for example, and shortening if not eliminating ski seasons in some regions such as New England. The regional or national economic impacts of such changes could be significant.
Many such changes are already being seen around the world. For example, the number of weather-related disasters experienced worldwide every year has been increasing over the past few decades. In the United States, the number of such disasters experienced each decade has risen fivefold since the 1970s. During the course of this century, average global surface temperatures are projected to increase at a rate unprecedented over at least the past 10,000 years, and scientists believe that rising temperatures could further increase the intensity and frequency of extreme weather events.
Q. What is the greenhouse effect, and is it affecting our climate?
A. The greenhouse effect is unquestionably real and helps to regulate the temperature of our planet. It is essential for life on Earth and is one of Earth's natural processes. It is the result of heat absorption by certain gases in the atmosphere (called greenhouse gases because they effectively 'trap' heat in the lower atmosphere) and re-radiation downward of some of that heat. Water vapor is the most abundant greenhouse gas, followed by carbon dioxide and other trace gases. Without a natural greenhouse effect, the temperature of the Earth would be about zero degrees F (-18°C) instead of its present 57°F (14°C). So, the concern is not with the fact that we have a greenhouse effect, but whether human activities are leading to an enhancement of the greenhouse effect by the emission of greenhouse gases through fossil fuel combustion and deforestation.
Q. Why do human-made greenhouse gases matter when water vapor is the most potent greenhouse gas?
A. The Earth's surface temperature would be about 34°C (61°F) colder than it is now if it were not for the natural heat trapping effect of greenhouse gases like carbon dioxide, methane, nitrous oxide, and water vapor. Indeed, water vapor is the most abundant and important of these naturally occurring greenhouse gases. In addition to its direct effect as a greenhouse gas, clouds formed from atmospheric water vapor also affect the heat balance of the Earth by reflecting sunlight (a cooling effect), and trapping infrared radiation (a heating effect).
However, just because water vapor is the most important gas in creating the natural greenhouse effect does not mean that human- made greenhouse gases are unimportant. Over the past ten thousand years, the amounts of the various greenhouse gases in the Earth's atmosphere remained relatively stable until a few centuries ago, when the concentrations of many of these gases began to increase due to industrialization, increasing demand for energy, rising population, and changing land use and human settlement patterns.
Accumulations of most of the human-made greenhouse gases are expected to continue to increase, so that, over the next 50 to 100 years, without control measures, they will produce a heat-trapping effect equivalent to more than a doubling of the pre-industrial carbon dioxide level.
Increasing amounts of human-made greenhouse gases would lead to an increase in the globally averaged surface temperature. However, as the temperature increases, other aspects of the climate will alter, including the amount of water vapor in the atmosphere. While human activities do not directly add significant amounts of water vapor to the atmosphere, warmer air contains more water vapor. Since water vapor is itself a greenhouse gas, global warming will be further enhanced by the increased amounts of water vapor. This sort of indirect effect is called a positive feedback.
It has been suggested that as greenhouse gases accumulate, the atmospheric events that generate cumulus clouds in tropical areas would cause a drying rather than moistening of the upper layers of the troposphere (the lowest region of the atmosphere). However, observations of the current atmosphere provide evidence for the conclusion that on a global scale, a warmed atmosphere will moisten and this will enhance greenhouse warming.
Clouds are another important factor in determining climate. The increased levels of water vapor in the atmosphere, as well as changes in temperatures and winds, will also cause changes in clouds that will alter the amount of energy from the sun that is absorbed and reflected by the Earth, at some locations enhancing and at others diminishing the warming due to greenhouse gases. The response of clouds to global warming is a major uncertainty in determining the magnitude and distribution of climate change.
Q. Are greenhouse gases increasing?
A. Human activity has been increasing the concentration of greenhouse gases in the atmosphere (mostly carbon dioxide from combustion of coal, oil, and gas; plus a few other trace gases). There is no scientific debate on this point. Pre-industrial levels of carbon dioxide (prior to the start of the Industrial Revolution) were about 280 parts per million by volume (ppmv), and current levels are greater than 380 ppmv and increasing at a rate of 1.9 ppm yr-1 since 2000. The global concentration of CO2 in our atmosphere today far exceeds the natural range over the last 650,000 years of 180 to 300 ppmv. According to the IPCC Special Report on Emission Scenarios (SRES), by the end of the 21st century, we could expect to see carbon dioxide concentrations of anywhere from 490 to 1260 ppm (75-350% above the pre-industrial concentration).
Q. Are El Niños related to global warming?
A. El Niños are not caused by global warming. Clear evidence exists from a variety of sources (including archaeological studies) that El Niños have been present for thousands, and some indicators suggest maybe millions, of years. However, it has been hypothesized that warmer global sea surface temperatures can enhance the El Niño phenomenon, and it is also true that El Niños have been more frequent and intense in recent decades. Whether El Niño occurrence changes with climate change is a major research question.
Q. Is the atmospheric/oceanic circulation changing?
A. A rather abrupt change in the El Niño - Southern Oscillation behavior occurred around 1976/77. Often called the climatic shift of 1976/77, this new regime has persisted. There have been relatively more frequent and persistent El Niño episodes rather than the cool episode La Niñas. This behavior is highly unusual in the last 130 years (the period of instrumental record). Changes in precipitation over the tropical Pacific are related to this change in the El Niño - Southern Oscillation, which has also affected the pattern and magnitude of surface temperatures. However, it is unclear as to whether this apparent change in the ENSO cycle is related to global warming.
Q. Is sea level rising?
A. Global mean sea level has been rising at an average rate of 1.7 mm/year (plus or minus 0.5mm) over the past 100 years, which is significantly larger than the rate averaged over the last several thousand years. Depending on which greenhouse gas increase scenario is used (high or low) projected sea-level rise is projected to be anywhere from 0.18 (low greenhouse gas increase) to 0.59 meters for the highest greenhouse gas increase scenario. However, this increase is due mainly to thermal expansion and contributions from melting alpine glaciers, and does not include any potential contributions from melting ice sheets in Greenland or Antarctica. Larger increases cannot be excluded but our current understanding of ice sheet dynamics renders uncertainties too large to be able to assess the likelihood of large-scale melting of these ice sheets.
A. Wealthier industrial countries contribute the most to global warming since they use most of the world’s fossil fuels. Europe, Japan, and North America—with roughly 15 percent of the world’s current population—are estimated to account for two-thirds of the carbon dioxide now in the atmosphere. With less than five percent of world population, the United States is the single-largest source of carbon from fossil fuels—emitting 24 percent of the world’s total. U.S. automobiles (more than 128 million, or one quarter of the world’s cars) emit roughly as much carbon as the entire Japanese economy, the world’s fourth-largest carbon emitter in 2000. China, despite being home to one-fifth of the world’s population and its heavy dependence on coal, ranks a distant second behind the U.S., emitting 12 percent of the global total. The average person in China produces less than one-eighth as much carbon dioxide as the average American.
Q. What is the Kyoto Protocol and what can it do to curb climate change?
A. The Kyoto Protocol is an international agreement, initially negotiated by government representatives meeting in Kyoto, Japan, in 1997, that sets targets to reduce the greenhouse gas emissions causing climate change. It requires a variety of actions by governments, including specific emission reduction requirements for industrial countries, as well as provisions to assist developing countries in limiting their emissions.
A. The Kyoto Protocol is an international agreement, initially negotiated by government representatives meeting in Kyoto, Japan, in 1997, that sets targets to reduce the greenhouse gas emissions causing climate change. It requires a variety of actions by governments, including specific emission reduction requirements for industrial countries, as well as provisions to assist developing countries in limiting their emissions.
For the Protocol to “enter into force,” it must be ratified by at least 55 nations representing 55 percent of industrial-country 1990 carbon dioxide emissions. As of as of 15 April 2004, 122 countries (representing 44.2 percent of industrial country 1990 emissions) had ratified or acceded to the Kyoto Protocol, including those of the European Union, Canada, Japan, and a host of developing countries. But because the world’s largest emitter—the United States—withdrew from Kyoto, the 55 percent threshold that allows the treaty to enter into force will be crossed only if Russia ratifies the agreement.
According to many studies, enforcing the Kyoto Protocol would protect the environment, reduce air pollution, and create new jobs in industries such as energy conservation, solar energy, wind power, and hydrogen technology, all of which could become powerful growth sectors in the decades ahead.
The Kyoto Protocol, during its first phase (through 2012) is a modest, yet important first step. Perhaps its greatest contribution in the short term will be to put in place mechanisms that can be built on, such as emissions trading and the transfer of clean technologies (such as renewable energy) to the developing world. Even though it hasn’t yet entered into force, it is already spurring corporations and governments to action, from the U.S. to the E.U. to Japan, and many developing countries as well.
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