Science Forums 2

[InfiniteNow]

I want to thank Turtle for bringing an opposing viewpoint. It's helpful to consider different perspectives when approaching an issue so complex.

I do though assert with confidence that the strawman/red herring argument of censorship and presumed heresy is one which I find hardly applies to the area of global climate change research. I shared some of my reasons for this viewpoint previously in this thread. Primarily, nobody is censoring deniers. It's just that nearly every attempt they make to refute the data fails upon scrutiny.



The recent posts above regarding volanism are important, but they do nothing to negate evidence surrounding human contributions of CO₂ to the atmosphere and the consequent impact on global climate. Volcanic forcing has been demonstrated to be a significantly smaller forcing factor than human emissions. Volcanic forcing must be considered, but it in no way negates the overall dominance of the impact humans contributions have on climate.


As I have said repeatedly in this thread, these issues have already been addressed by my sources. Nobody has argued against volcanism's impact, just the relative scope of it. Please also note that nobody has succesfully challenged the validity of any of the data I have provided. It's unfortunate people are not reading them (or, completely ignoring them), and it's further unfortunate that so many false claims have been presented here to our readers.


Speaking specifically to the issue of volcanism, please see the excerpts below. I welcome challenges to the data. I welcome healthy debate. I discourage logical fallacies like strawmen, red herrings, false dichotomies, ad hominems, and all types of appeals (to ignorance, to shame, to ridicule, etc.).


If you wish to challenge the data I've presented, please do so. Posting of links from non-peer reviewed sources or from articles that have already thoroughly been debunked should be avoided.



http://www.ipcc.ch/pdf/assessment-re...1-chapter2.pdf

The combined anthropogenic RF is estimated to be +1.6 [–1.0, +0.8]2 W m^–2, indicating that, since 1750, it is extremely likely that humans have exerted a substantial warming influence on climate. This RF estimate is likely to be at least five times greater than that due to solar irradiance changes. For the period 1950 to 2005, it is exceptionally unlikely that the combined natural RF (solar irradiance plus volcanic aerosol) has had a warming influence comparable to that of the combined anthropogenic RF.

Since the start of the industrial era (about 1750), the overall effect of human activities on climate has been a warming influence. The human impact on climate during this era greatly exceeds that due to known changes in natural processes, such as solar changes and volcanic eruptions.

http://www.ipcc.ch/pdf/assessment-re...1-chapter9.pdf

Simulations of global mean 20th-century temperature change that accounted for anthropogenic greenhouse gases and sulphate aerosols as well as solar and volcanic forcing were found to be generally consistent with observations. In contrast, a limited number of simulations of the response to known natural forcings alone indicated that these may have contributed to the observed warming in the first half of the 20th century, but could not provide an adequate explanation of the warming in the second half of the 20th century, nor the observed changes in the vertical structure of the atmosphere.

Differences in the temporal evolution and sometimes the spatial pattern of climate response to external forcing make it possible, with limitations, to separate the response to these forcings in observations, such as the responses to greenhouse gas and sulphate aerosol forcing. In contrast, the climate response and temporal evolution of other anthropogenic forcings is more uncertain, making the simulation of the climate response and its detection in observations more difficult. The temporal evolution, and to some extent the spatial and vertical pattern, of the climate response to natural forcings is also quite different from that of anthropogenic forcing. This makes it possible to separate the climate response to solar and volcanic forcing from the response to anthropogenic forcing despite the uncertainty in the history of solar forcing noted above.

It is very unlikely that the 20th-century warming can be explained by natural causes. The late 20th century has been unusually warm. Palaeoclimatic reconstructions show that the second half of the 20th century was likely the warmest 50-year period in the Northern Hemisphere in the last 1300 years. This rapid warming is consistent with the scientific understanding of how the climate should respond to a rapid increase in greenhouse gases like that which has occurred over the past century, and the warming is inconsistent with the scientific understanding of how the climate should respond to natural external factors such as variability in solar output and volcanic activity.

Nevertheless, ozone, solar and volcanic forcing changes are generally not found to have made a large contribution to the observed NAM trend over recent decades (Shindell et al., 2001a; Gillett et al., 2003a).

Although natural internal climate processes, such as El Niño, can cause variations in global mean temperature for relatively short periods, analysis indicates that a large portion is due to external factors. Brief periods of global cooling have followed major volcanic eruptions, such as Mt. Pinatubo in 1991. In the early part of the 20th century, global average temperature rose, during which time greenhouse gas concentrations started to rise, solar output was probably increasing and there was little volcanic activity. During the 1950s and 1960s, average global temperatures levelled off, as increases in aerosols from fossil fuels and other sources cooled the planet. The eruption of Mt. Agung in 1963 also put large quantities of reflective dust into the upper atmosphere. The rapid warming observed since the 1970s has occurred in a period when the increase in greenhouse gases has dominated over all other factors.

In addition, differences in the timing of the human and natural external influences help to distinguish the climate responses to these factors. Such considerations increase confidence that human rather than natural factors were the dominant cause of the global warming observed over the last 50 years.

Estimates of Northern Hemisphere temperatures over the last one to two millennia, based on natural ‘thermometers’ such as tree rings that vary in width or density as temperatures change, and historical weather records, provide additional evidence that the 20th-century warming cannot be explained by only natural internal variability and natural external forcing factors. Confidence in these estimates is increased because prior to the industrial era, much of the variation they show in Northern Hemisphere average temperatures can be explained by episodic cooling caused by large volcanic eruptions and by changes in the Sun’s output. The remaining variation is generally consistent with the variability simulated by climate models in the absence of natural and human-induced external factors. While there is uncertainty in the estimates of past temperatures, they show that it is likely that the second half of the 20th century was the warmest 50-year period in the last 1300 years. The estimated climate variability caused by natural factors is small compared to the strong 20th-century warming.

Chapter 2 concludes that it is exceptionally unlikely that the combined natural (solar and volcanic) radiative forcing has had a warming influence comparable to that of the combined anthropogenic forcing over the period 1950 to 2005.

Since my previous posts seem to have gone ignored, I hope the above is specific enough to warrant attention and due consideration.