Originally posted by Hand of Hecate
Climate change. I hate that crap. I also hate that some fundamentally basic concepts could be implemented to drastically reduce our dependence on fossil fuels. I also hate that our decision makers seem to have dug some extraordinarily deep and well funded holes to bury their heads in.
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions, or in the distribution of weather around the average conditions (i.e., more or fewer extreme weather events). Climate change is caused by factors such as biotic processes, variations in solar radiation received by Earth, plate tectonics, and volcanic eruptions. Certain human activities have also been identified as significant causes of recent climate change, often referred to as "global warming".[1]
Scientists actively work to understand past and future climate by using observations and theoretical models. A climate record — extending deep into the Earth's past — has been assembled, and continues to be built up, based on geological evidence from borehole temperature profiles, cores removed from deep accumulations of ice, floral and faunal records, glacial and periglacial processes, stable-isotope and other analyses of sediment layers, and records of past sea levels. More recent data are provided by the instrumental record. General circulation models, based on the physical sciences, are often used in theoretical approaches to match past climate data, make future projections, and link causes and effects in climate change.
Contents [hide]
1 Terminology
2 Causes
2.1 Internal forcing mechanisms
2.1.1 Ocean variability
2.1.2 Life
2.2 External forcing mechanisms
2.2.1 Orbital variations
2.2.2 Solar output
2.2.3 Volcanism
2.2.4 Plate tectonics
2.2.5 Human influences
3 Physical evidence
3.1 Temperature measurements and proxies
3.2 Historical and archaeological evidence
3.3 Glaciers
3.4 Arctic sea ice loss
3.5 Vegetation
3.6 Pollen analysis
3.7 Precipitation
3.8 Dendroclimatology
3.9 Ice cores
3.10 Animals
3.11 Sea level change
4 See also
5 Notes
6 References
7 Further reading
8 External links
Terminology
The most general definition of climate change is a change in the statistical properties of the climate system when considered over long periods of time, regardless of cause.[2] Accordingly, fluctuations over periods shorter than a few decades, such as El Niño, do not represent climate change.
The term sometimes is used to refer specifically to climate change caused by human activity, as opposed to changes in climate that may have resulted as part of Earth's natural processes.[3] In this sense, especially in the context of environmental policy, the term climate change has become synonymous with anthropogenic global warming. Within scientific journals, global warming refers to surface temperature increases while climate change includes global warming and everything else that increasing greenhouse gas levels will affect.[4]
Causes
On the broadest scale, the rate at which energy is received from the sun and the rate at which it is lost to space determine the equilibrium temperature and climate of Earth. This energy is distributed around the globe by winds, ocean currents, and other mechanisms to affect the climates of different regions.
Factors that can shape climate are called climate forcings or "forcing mechanisms".[5] These include processes such as variations in solar radiation, variations in the Earth's orbit, mountain-building and continental drift and changes in greenhouse gas concentrations. There are a variety of climate change feedbacks that can either amplify or diminish the initial forcing. Some parts of the climate system, such as the oceans and ice caps, respond slowly in reaction to climate forcings, while others respond more quickly.
Forcing mechanisms can be either "internal" or "external". Internal forcing mechanisms are natural processes within the climate system itself (e.g., the thermohaline circulation). External forcing mechanisms can be either natural (e.g., changes in solar output) or anthropogenic (e.g., increased emissions of greenhouse gases).
Whether the initial forcing mechanism is internal or external, the response of the climate system might be fast (e.g., a sudden cooling due to airborne volcanic ash reflecting sunlight), slow (e.g. thermal expansion of warming ocean water), or a combination (e.g., sudden loss of albedo in the arctic ocean as sea ice melts, followed by more gradual thermal expansion of the water). Therefore, the climate system can respond abruptly, but the full response to forcing mechanisms might not be fully developed for centuries or even longer.
Internal forcing mechanisms
Scientists generally define the five components of earth's climate system to include atmosphere, hydrosphere, cryosphere, lithosphere (restricted to the surface soils, rocks, and sediments), and biosphere.[6] Natural changes in the climate system ("internal forcings"😉 result in internal "climate variability".[7] Examples include the type and distribution of species, and changes in ocean currents.
Ocean variability
Main article: Thermohaline circulation
Pacific Decadal Oscillation 1925 to 2010
The ocean is a fundamental part of the climate system, some changes in it occurring at longer timescales than in the atmosphere, massing hundreds of times more and having very high thermal inertia (such as the ocean depths still lagging today in temperature adjustment from the Little Ice Age).[clarification needed][8]
Short-term fluctuations (years to a few decades) such as the El Niño-Southern Oscillation, the Pacific decadal oscillation, the North Atlantic oscillation, and the Arctic oscillation, represent climate variability rather than climate change. On longer time scales, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat by carrying out a very slow and extremely deep movement of water and the long-term redistribution of heat in the world's oceans.
A schematic of modern thermohaline circulation. Tens of millions of years ago, continental plate movement formed a land-free gap around Antarctica, allowing formation of the ACC which keeps warm waters away from Antarctica.
Life
Life affects climate through its role in the carbon and water cycles and such mechanisms as albedo, evapotranspiration, cloud formation, and weathering.[9][10][11] Examples of how life may have affected past climate include: glaciation 2.3 billion years ago triggered by the evolution of oxygenic photosynthesis,[12][13] glaciation 300 million years ago ushered in by long-term burial of decomposition-resistant detritus of vascular land plants (forming coal),[14][15] termination of the Paleocene-Eocene Thermal Maximum 55 million years ago by flourishing marine phytoplankton,[16][17] reversal of global warming 49 million years ago by 800,000 years of arctic azolla blooms,[18][19] and global cooling over the past 40 million years driven by the expansion of grass-grazer ecosystems.[20][21]
External forcing mechanisms
Increase in atmospheric CO
2 levels
Milankovitch cycles from 800,000 years ago in the past to 800,000 years in the future.
Variations in CO2, temperature and dust from the Vostok ice core over the last 450,000 years
Orbital variations
Main article: Milankovitch cycles
Slight variations in Earth's orbit lead to changes in the seasonal distribution of sunlight reaching the Earth's surface and how it is distributed across the globe. There is very little change to the area-averaged annually averaged sunshine; but there can be strong changes in the geographical and seasonal distribution. The three types of orbital variations are variations in Earth's eccentricity, changes in the tilt angle of Earth's axis of rotation, and precession of Earth's axis. Combined together, these produce Milankovitch cycles which have a large impact on climate and are notable for their correlation to glacial and interglacial periods,[22] their correlation with the advance and retreat of the Sahara,[22] and for their appearance in the stratigraphic record.[23]
The IPCC notes that Milankovitch cycles drove the ice age cycles, CO2 followed temperature change "with a lag of some hundreds of years," and that as a feedback amplified temperature change.[24] The depths of the ocean have a lag time in changing temperature (thermal inertia on such scale). Upon seawater temperature change, the solubility of CO2 in the oceans changed, as well as other factors impacting air-sea CO2 exchange.[25]
Solar output
Main article: Solar variation
Variations in solar activity during the last several centuries based on observations of sunspots and beryllium isotopes. The period of extraordinarily few sunspots in the late 17th century was the Maunder minimum.
The Sun is the predominant source of energy input to the Earth. Both long- and short-term variations in solar intensity are known to affect global climate.
Three to four billion years ago the sun emitted only 70% as much power as it does today. If the atmospheric composition had been the same as today, liquid water should not have existed on Earth. However, there is evidence for the presence of water on the early Earth, in the Hadean[26][27] and Archean[28][26] eons, leading to what is known as the faint young Sun paradox.[29] Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist.[30] Over the following approximately 4 billion years, the energy output of the sun increased and atmospheric composition changed. The Great Oxygenation Event – oxygenation of the atmosphere around 2.4 billion years ago – was the most notable alteration. Over the next five billion years the sun's ultimate death as it becomes a red giant and then a white dwarf will have large effects on climate, with the red giant phase possibly ending any life on Earth that survives until that time.
Solar output also varies on shorter time scales, including the 11-year solar cycle[31] and lon...
14 May '14 21:11
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