Policy statement of the AMS

[Old Rocks]

This is what the American Meteorological Society has to say on global warming.

2012 AMS Information Statement on Climate Change

How is climate changing?

Warming of the climate system now is unequivocal, 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. Surface 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. Nevertheless, 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 in more than a century of global records. The warming trend is greatest in northern high latitudes and over land. In the U.S., most of the observed warming has occurred in the West and in Alaska; for the nation as a whole, there have been twice as many record daily high temperatures as record daily low temperatures in the first decade of the 21st century.

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 ice. 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 more frequently 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 and insects.

 

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The assessment of the American Chemical Society

Global Climate Change

The range of observed and potential climate change impacts identified by the ACC assessment include a warmer climate with more extreme weather events, significant sea level rise, more constrained fresh water sources, deterioration or loss of key land and marine ecosystems, and reduced food resources— many of which may pose serious public health threats. (NRC, 2010a) The effects of an unmitigated rate of climate change on key Earth system components, ecological systems, and human society over the next 50 years are likely to be severe and possibly irreversible on century time scales.

 

[Old Rocks]

The Geological Society of America. Pretty unequivacal statement from geologists.

The Geological Society of America - Position Statement on Climate Change

Greenhouse gases remain as the major explanation for the warming. Observations and climate model assessments of the natural and anthropogenic factors responsible for this warming conclude that rising anthropogenic emissions of greenhouse gases have been an increasingly important contributor since the mid-1800s and the major factor since the mid-1900s (Meehl et al., 2004). The CO2 concentration in the atmosphere is now ~30% higher than peak levels that have been measured in ice cores spanning 800,000 years of age, and the methane concentration is 2.5 times higher. About half of Earth’s warming has occurred through the basic heat-trapping effect of the gases in the absence of any feedback processes. This “clear-sky” response to climate is known with high certainty. The other half of the estimated warming results from the net effect of feedbacks in the climate system: a large positive feedback from water vapor; a smaller positive feedback from snow and ice albedo; a negative feedback from aerosols, and still uncertain,feedbacks from clouds. The vertical structure of observed changes in temperature and water vapor in the troposphere is consistent with the anthropogenic greenhouse-gas “fingerprint” simulated by climate models (Santer et al., 2008). Considered in isolation, the greenhouse-gas increases during the last 150 years would have caused a warming larger than that actually measured, but negative feedback from aerosols and possibly clouds has offset part of the warming. In addition, because the oceans take decades to centuries to respond fully to climatic forcing, the climate system has yet to register the full effect of gas increases in recent decades.

These advances in scientific understanding of recent warming form the basis for projections of future changes. If greenhouse-gas emissions follow predicted trajectories, by 2100 atmospheric CO2 concentrations will reach two to four times pre-industrial levels, for a total warming of 2 °C to 4.5 °C compared to 1850. This range of changes in greenhouse gas concentrations and temperature would substantially alter the functioning of the planet in many ways. The projected changes involve risk to humans and other species: (1) continued shrinking of Arctic sea ice with effects on native cultures and ice-dependent biota; (2) less snow accumulation and earlier melt in mountains, with reductions in spring and summer runoff for agricultural and municipal water; (3) disappearance of mountain glaciers and their late-summer runoff; (4) increased evaporation from farmland soils and stress on crops; (5) greater soil erosion due to increases in heavy convective summer rainfall; (6) longer fire seasons and increases in fire frequency; (7) severe insect outbreaks in vulnerable forests; (8) acidification of the global ocean; and (9) fundamental changes in the composition, functioning, and biodiversity of many terrestrial and marine ecosystems. In addition, melting of Greenland and West Antarctic ice (still highly uncertain as to amount), along with thermal expansion of seawater and melting of mountain glaciers and small ice caps, will cause substantial future sea-level rise, affecting densely populated coastal regions, inundating farmland and dislocating large populations. Because large, abrupt climatic changes occurred within spans of just decades during previous ice-sheet fluctuations, the possibility exists for rapid future changes as ice sheets become vulnerable to large greenhouse-gas increases. Finally, carbon-climate model simulations indicate that 10–20% of the anthropogenic CO2 “pulse” could stay in the atmosphere for thousands of years, extending the duration of fossil-fuel warming and its effects on humans and other species. The acidification of the global ocean and its effects on ocean life are projected to last for tens of thousands of years.

 

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http://sciencepolicy.agu.org/files/2013/07/AGU-Climate-Change-Position-Statement_August-2013.pdf

Human‐Induced Climate Change Requires Urgent Action

Humanity is the major influence on the global climate change observed over the past 50 years. Rapid societal responses can significantly lessen negative outcomes. Human activities are changing Earth’s climate. At the global level, atmospheric concentrations of carbon dioxide and other heat‐trapping greenhouse gases have increased sharply since the Industrial Revolution. Fossil fuel burning dominates this increase. Human‐caused increases in greenhouse gases are responsible for most of the observed
global average surface warming of roughly 0.8°C (1.5°F) over the past 140 years. Because natural processes cannot quickly remove some of these gases (notably carbon dioxide) from the atmosphere, our past, present, and future emissions will influence the climate system for millennia.

Extensive, independent observations confirm the reality of global warming. These observations show atmospheric water vapor; they document decreases in the extent of mountain glaciers, snow cover, permafrost, and Arctic sea ice. These changes are broadly consistent with long understood physics and predictions of how the climate system is expected to respond to human‐caused increases in greenhouse gases. The changes are inconsistent with explanations of climate change that rely on known natural influences.