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AMS statement Climate Change March 2012
#1
I suppose this is best described as "government approved science".
Read it and weep.


Climate Change

An Information Statement of the American Meteorological Society


(Adopted by AMS Council on ? March 2012)


Bull. Amer. Met. Soc., 93

The following is an AMS Information Statement intended to provide a trustworthy, objective, and scientifically up-to-date explanation of scientific issues of concern to the public at large.

Background

This statement provides a brief overview of how and why global climate has changed in recent decades and will continue to change in the future. It is based on the peer-reviewed scientific literature and is consistent with the vast weight of current scientific understanding as expressed in assessments and reports from the Intergovernmental Panel on Climate Change, the U.S. National Academy of Sciences, and the U.S. Climate Change Science Program. Although the statement has been drafted in the context of concerns in the United States, the underlying issues are inherently global in nature.

How is climate changing?

Earth’s climate is now unambiguously warming, according to many different kinds of evidence. Observations show increases in globally averaged air and ocean temperatures, as well as widespread melting of snow and ice and rising globally averaged sea level. Temperature data for Earth as a whole, including readings over both land and ocean, show an increase of about 0.8°C (1.4°F) over the period 1901-2010 and about 0.5°C (0.9°F) over the period 1979-2010 (the era for which satellite-based temperature data are routinely available). Due to natural variability, not every year is warmer than the preceding year globally, but every decade since the 1970s has been warmer than the previous decade. All of the 10 warmest years in the global temperature records up to 2011 have occurred since 1997, with 2005 and 2010 being the warmest two years on record in more than a century of global records. The warming trend is greatest in northern high latitudes, over land, and at night. In the U.S., most of the observed warming has occurred in the West and in Alaska; for the nation as a whole, the last decade has seen more than twice as many record daily high temperatures as record daily low temperatures.
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The effects of this warming are especially evident in the planet’s polar regions. Arctic sea ice extent and volume have been decreasing for the past several decades. Both the Greenland and Antarctic ice sheets have lost significant amounts of mass. Most of the world’s glaciers are in retreat.

Other changes, globally and in the U.S., are also occurring at the same time. The amount of rain falling in very heavy precipitation events (the heaviest 1% of all precipitation events) has increased over the last 50 years throughout the U.S. Freezing levels are rising in elevation, with rain occurring instead of snow at mid-elevations of western mountains. Spring maximum snowpack is decreasing, snowmelt occurs earlier, and the spring runoff that supplies over two-thirds of western U.S. streamflow is reduced. Evidence for warming is also observed in seasonal changes across many areas, including earlier springs, longer frost-free periods, longer growing seasons, and shifts in natural habitats and in migratory patterns of birds.

Globally averaged sea level has risen by about 18 cm (7 inches) since 1900, with the rise accelerating since the early 1990s. About half of the sea level rise observed since the 1970s has been caused by water expansion due to increases in ocean temperatures. Sea level is also rising due to melting from continental glaciers and from ice sheets on both Greenland and Antarctica. Locally, sea level changes can depend also on slowly rising or falling land, which results in some local sea level changes much larger or smaller than the global average. Even small rises in sea level in coastal zones are expected to lead to potentially severe impacts, especially in small island nations and in other regions that experience storm surges associated with vigorous weather systems.

Why is climate changing?

There are multiple causes of climate change always operating, but it is widely accepted that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO


2), chlorofluorocarbons, methane, nitrous oxide, and ozone. The most important of these over the long term is CO2, whose concentration in the atmosphere is rising principally as a result of fossil fuel combustion, deforestation, and cement manufacture. While large amounts of CO2 enter and leave the atmosphere through natural processes, these human activities are increasing the total amount in the air. Approximately half of the CO2 put into the atmosphere through human activity
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in the past 250 years has been taken up by the ocean and terrestrial biosphere, with the other half remaining in the atmosphere. Since long-term measurements began in the 1950s, the atmospheric CO


2 concentration has been increasing at a rate much faster than for any observed period in the geological record. It would take a thousand years for the majority of the carbon dioxide added by humans to the atmosphere to be removed by natural processes, and much of it will remain for thousands of years.

Water vapor also is an important atmospheric greenhouse gas. Unlike other greenhouse gases, however, the concentration of water vapor is controlled by the global climate system through its hydrological cycle of evaporation-condensation-precipitation. Water vapor is highly variable in space and time with a short lifetime, because of weather variability. Observations indicate an increase in global average water vapor in the atmosphere in recent decades, and this is consistent with the response produced by climate models that simulate human-induced increases in greenhouse gases. This increase in water vapor also enhances the greenhouse effect, amplifying the impact of human-induced increases in other greenhouse gases.

Human activity also affects climate through changes in the number and physical properties of tiny solid particles and liquid droplets in the atmosphere, known collectively as atmospheric aerosols, and through changes in the land surface. Atmospheric aerosols include dust, sea salt, and air pollution. Aerosols have a variety of effects: They absorb and redirect solar energy from the sun and heat energy emitted by Earth, emit energy themselves, and modify the ability of clouds to reflect sunlight and to produce precipitation. Aerosols can both strengthen and weaken greenhouse warming, depending on their characteristics. Most aerosols originating from human activity act to cool the planet and so partly counteract greenhouse gas warming effects. Aerosols lofted into the stratosphere (between about 13 km/7 miles and 50 km/30 miles altitude above the surface) by occasional large sulfur-rich volcanic eruptions can reduce global surface temperature for several years. By contrast, carbon soot from incomplete combustion of fossil fuels and plants warms the planet, so that decreases in soot would reduce warming. Aerosols have lifetimes in the troposphere (up to approximately 13 km/7 miles from the surface in the middle latitudes) on the order of one week, much shorter than that of most greenhouse gases, and their prevalence and properties can vary widely by region.

Changes in the land surface also change its exchanges of water and energy with the atmosphere. Humans alter land surface characteristics by carrying out irrigation, removing and
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introducing forests, changing vegetative land cover through agriculture, and building cities and reservoirs. These changes can have significant effects on regional and local climate patterns, which adds up to a small impact on global energy balance as well.

How can climate change be projected into the future?

Factors that have altered climate throughout history, both human (such as human emission of greenhouse gases) and natural (such as variation of solar irradiance and volcanic eruptions), will continue to alter climate in the future. Climate projections for decades into the future are made using complex numerical models of the climate system that account for changes in the flow of energy into and out of the Earth system on time scales much longer than the prediction limit for individual weather systems of about two weeks.. These models simulate the important aspects of climate and climate change based on fundamental physical laws of motion, thermodynamics, and radiative transfer. Projections of future climate typically cover a range of possibilities, in part because of differences among models, in part because long-term predictions of natural variations (e.g., volcanic eruptions and El Niño events), are not possible, and in part because it is not known exactly how greenhouse gas emissions will evolve in future decades. Future emissions will depend on global social and economic development, and on the extent and impact of mitigation activities designed to reduce greenhouse gas and black carbon emissions. As a result, climate scientists investigate a range of "scenarios" for future emissions and report how climate would change in response to each scenario.

Changes in the means and extremes of temperature and precipitation in response to increasing greenhouse gases can be projected over decades to centuries, even though the timing of individual weather events cannot be predicted on this time scale. Because it would take many years for nature to verify whether a future climate projection is correct, researchers establish confidence in these projections by using historical and paleoclimate evidence and through careful study of observations of the causal chain between energy flow changes and climate pattern responses. A valuable demonstration of the validity of current climate models is that when they include all known natural and human-induced factors that influence the global atmosphere on a large scale, the models reproduce many important aspects of observed changes of 20


th-century climate, including (1) global, continental, and sub-continental mean and extreme temperatures, (2) Arctic sea ice extent, (3) the latitudinal distribution of precipitation, (4) extreme precipitation frequency.
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Model limitations include inadequate representations of some important processes and details. For example, the complex dynamical, radiative, and microphysical processes involved in the evolution of a cloud or the spatially variable nature of soil moisture are not yet able to be treated fully by a typical climate model. In spite of these limitations, climate models have demonstrated skill in reproducing past climates, and they agree on the broad direction of future climate.

How is the climate expected to change in the future?

Future warming of the climate is inevitable for many years, due to the greenhouse gases already added to the atmosphere and the heat that has been taken up by the oceans, unless carbon capture and storage measures or other geoengineering approaches such as reflecting sunlight can be devised. However, the potential risks of geoengineering may be quite large, and more study of the topic is needed (see AMS statement on geoengineering).

The projections in the rest of this section largely are based on simulations conducted with climate models, and assume that the amount of greenhouse gas in the atmosphere will continue to increase due to human activity. In general, many of the trends in the climate system observed in recent decades are projected to continue. Confidence in the projections is higher for temperature than for other climate elements such as rainfall, and higher at the global and continental scales than for the regional and local scales. The model projections show that the largest warming will occur in northern polar regions, over land areas, and in the winter season, consistent with observed trends.

In the coming century, global sea level also will continue to rise. With its large mass and high capacity for heat storage, the ocean will continue to slowly warm to greater depths and thus thermally expand for several centuries. Model simulations project about 20 cm (8 inches) of sea level rise due to thermal expansion in the 21


st century. Moreover, paleoclimatic observations and ice sheet modeling indicate that melting of the Greenland and the West Antarctic ice sheets will eventually cause global sea level to rise several additional meters if warming continues at its present rate beyond the 21st century. Even greater sea level rise would occur further into the future as long as greenhouse gas concentrations continue to increase.
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Atmospheric water vapor and liquid water content will increase globally, consistent with warmer temperatures, and consequently the global hydrological cycle will continue to accelerate. For many areas, model simulations suggest there will be a tendency towards more intense rain and snow events separated by longer periods without precipitation. However, changes in precipitation patterns are expected to differ considerably by region and by season. In some regions, the accelerated hydrological cycle will likely act to reinforce existing patterns of precipitation, leading to more severe droughts and floods. Further poleward, the greater warming at high latitudes and over land likely will change the large-scale atmospheric circulation, leading to significant regional shifts in precipitation patterns. For example, the model simulations suggest that precipitation will likely increase in the far northern parts of North America and decrease in the southwest and south central United States.

These simulations further indicate that heavy precipitation events will very likely continue to intensify, and so increase precipitation totals from the strongest storms, with important implications for water resource management and flooding. The simulations also indicate the likelihood of longer dry spells between precipitation events in the subtropics and lower middle latitudes, with shorter dry spells projected for higher latitudes where mean precipitation is expected to increase. Continued warming also implies a reduction of winter snow accumulations in favor of rain in many places, and thus a reduced spring snowpack. Rivers now fed by snowmelt will experience earlier spring peaks and reduced dry-season flows. Widespread retreat of mountain glaciers is expected to eventually lead to reduced dry season flows for glacier-fed rivers. Drought is projected to increase over the North American continental interior, and particularly the southwest United States. However, decadal-scale variations in world ocean conditions could offset or enhance such changes in the next few decades. For the longer-term, paleoclimatic observations suggest that droughts lasting decades are possible and that these prolonged droughts could occur with little warning.

Weather patterns will continue to vary from day to day and from season to season, but the frequency of particular patterns and extreme weather and climate events may change. Model simulations project an increased global proportion of hurricanes that are in the strongest categories, namely 4 and 5 on the Saffir-Simpson scale, though the total counts of hurricanes may not change or may even decrease. Some regional variations in these trends are possible.. Simulations also indicate that midlatitude storm tracks will shift poleward.. Interannual variations of important large-scale climate conditions (such as El Niño and La Niña) will also continue to
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occur, but there may be changes in their intensity, frequency, and other characteristics, resulting in different responses by the atmosphere. Heat waves and cold snaps, and the weather conditions giving rise to them, will continue to occur, but proportionately more extreme warm periods and fewer cold periods are expected. Indeed, what many people consider a cold wave is already changing towards less severe conditions. Frost days (those with minimum temperature below freezing) will be fewer and growing seasons longer. Drier conditions in summer, such as those anticipated for the southern United States and southern Europe, are expected to contribute to more severe episodes of extreme heat. Critical thresholds of daily maximum temperature, above which ecosystems and crop systems (e.g., food crops such as rice, corn, and wheat) suffer increasingly severe damage, are likely to be exceeded more frequently.

The Earth system is highly interconnected and complex, with many processes and feedbacks that only slowly are becoming understood. In particular, the carbon cycle remains a large source of uncertainty for the projection of future climate. It is unclear if the land biosphere and oceans will be able to continue taking up carbon at their current rate into the future; one issue is whether soil and vegetation will become a global source rather than a sink of carbon as the planet warms. The portion of the increased CO


2 release that is absorbed by the world ocean is making the ocean more acidic, with negative implications for shell- and skeleton-forming organisms and more generally for ocean ecosystems. There are indications that large regions of permafrost in parts of Alaska and other northern polar areas are already melting, with the potential to release massive amounts of carbon into the atmosphere beyond those being added by human activity. These processes are only now being quantified by observation and introduced into climate models, and significant research is required to fully understand their potential impact.

Final remarks

There is unequivocal evidence that Earth’s atmosphere, ocean, and land surface are warming; sea level is rising; and snow cover, mountain glaciers, and Arctic sea ice are shrinking. The overwhelmingly dominant cause of the warming since the 1950s is widely accepted to be human activities. The observed warming will be irreversible for many years into the future, and even greater warming will occur as greenhouse gases continue to accumulate in the atmosphere. Avoiding even part of this future warming will require a large and rapid reduction in
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global greenhouse gas emissions. The ongoing warming will increase risks to human societies, economies, ecosystems, and wildlife through the 21


st century and beyond, making it imperative that society adapt to a changing climate. To inform decisions on adaptation and mitigation, it is critical that we improve our understanding of the global climate system and our ability to project future climate through continued and improved monitoring and research. This is especially true for smaller (seasonal and regional) scales and weather and climate extremes, and for important hydroclimatic variables such as precipitation and water availability.

Technological, economic, and policy choices in the near future will determine the extent of future impacts of climate change. Policy decisions are seldom made in a context of absolute certainty. The policy debate should include consideration of the best ways to both adapt to and mitigate climate change. Mitigation will reduce the amount of future climate change and the risk of impacts that are potentially large and dangerous. At the same time, some continued climate change is inevitable, and policy responses should include adaptation to climate change. Prudence dictates extreme care in managing our relationship with the only planet known to be capable of sustaining human life.
[This statement is considered in force until March 2017 unless superseded by a new statement issued by the AMS Council before this date.]
The whole aim of practical politics is to keep the populace alarmed
(and hence clamorous to be led to safety)
by menacing it with an endless series of hobgoblins, all of them imaginary.

H. L. Mencken.  

The hobgoblins have to be imaginary so that
"they" can offer their solutions, not THE solutions.
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#2
""This statement is considered in force until March 2017. . . .""

The only bit that made me smile. As for the rest of the statement, I consider it in the class of "Crime against humanity". Angry
Environmentalism is based on lies and the lies reflect an agenda that regards humanity as the enemy of the Earth. - Alan Caruba
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