M
Michaelo
Guest
I’ve already touched on this, but I will try to be more thorough. Also, I will continue to quote directly from sources so that I don’t lose anything in translation.Before you can lay claim to man-made anything, you need to show what changes occurred in the past in order to show why this change is somehow different.
With regards to past climate changes caused by natural factors:
Causes of Change Prior to the Industrial Era (pre-1780)
Known causes, “drivers” or “forcings” of past climate change include:
sourceCode:* **Changes in the Earth's orbit**: Changes in the shape of the Earth's orbit (or eccentricity) as well as the Earth's tilt and precession affect the amount of sunlight received on the Earth's surface. These orbital processes -- which function in cycles of 100,000 (eccentricity), 41,000 (tilt), and 19,000 to 23,000 (precession) years -- are thought to be the most significant drivers of ice ages according to the theory of Mulitin Milankovitch, a Serbian mathematician (1879-1958). The National Aeronautics and Space Administration's (NASA) Earth Observatory offers additional information about orbital variations and the Milankovitch Theory. * **Changes in the sun's intensity**: Changes occurring within (or inside) the sun can affect the intensity of the sunlight that reaches the Earth's surface. The intensity of the sunlight can cause either warming (for stronger solar intensity) or cooling (for weaker solar intensity). According to NASA research, reduced solar activity from the 1400s to the 1700s was likely a key factor in the “Little Ice Age” which resulted in a slight cooling of North America, Europe and probably other areas around the globe. (See additional discussion under The Last 2,000 Years.) * **Volcanic eruptions**: Volcanoes can affect the climate because they can emit aerosols and carbon dioxide into the atmosphere. o Aerosol emissions: Volcanic aerosols tend to block sunlight and contribute to short term cooling. Aerosols do not produce long-term change because they leave the atmosphere not long after they are emitted. According to the United States Geological Survey (USGS), the eruption of the Tambora Volcano in Indonesia in 1815 lowered global temperatures by as much as 5ºF and historical accounts in New England describe 1816 as “the year without a summer.” o Carbon dioxide emissions: Volcanoes also emit carbon dioxide (CO2), a greenhouse gas, which has a warming effect. For about two-thirds of the last 400 million years, geologic evidence suggests CO2 levels and temperatures were considerably higher than present. One theory is that volcanic eruptions from rapid sea floor spreading elevated CO2 concentrations, enhancing the greenhouse effect and raising temperatures. However, the evidence for this theory is not conclusive and there are alternative explanations for historic CO2 levels (NRC, 2005). While volcanoes may have raised pre-historic CO2 levels and temperatures, according to the USGS Volcano Hazards Program, human activities now emit 130 times as much CO2 as volcanoes (whose emissions are relatively modest compared to some earlier times).
And for more detail on each of these drivers…
- Changes in Earth’s orbit:
sourceIn addition to changes in energy from the sun itself, the Earth’s position and orientation relative to the sun (our orbit) also varies slightly, thereby bringing us closer and further away from the sun in predictable cycles (called Milankovitch cycles). Variations in these cycles are believed to be the cause of Earth’s ice-ages (glacials). Particularly important for the development of glacials is the radiation receipt at high northern latitudes. Diminishing radiation at these latitudes during the summer months would have enabled winter snow and ice cover to persist throughout the year, eventually leading to a permanent snow- or icepack. While Milankovitch cycles have tremendous value as a theory to explain ice-ages and long-term changes in the climate, they are unlikely to have very much impact on the decade-century timescale. Over several centuries, it may be possible to observe the effect of these orbital parameters, however for the prediction of climate change in the 21st century, these changes will be far less important than radiative forcing from greenhouse gases.