During a Congressional hearing for U.S. House of Representatives Committee on Science Space and Technology, Dr. John Christy made the following statement:During a Congressional hearing for U.S. House of Representatives Committee on Science Space and Technology, Dr. John Christy made the following statement:
"I think there's been too much jumping to conclusions about seeing something happening in the climate and saying 'well the only way that can happen is human effects"
But are scientists really jumping to conclusions? Scientists are well aware that the recent climate events, or any climate events for that matter, can be caused by variability in the natural world. It is well established that human emissions are not the only variable in forcing the climate to change. For example, slow changes occur constantly due to orbital factors and the Earth's tilt; and faster changes occur due to natural cycles like the El Nino Southern Oscillation (ENSO), but the questions that this committee set out to answer were (i) whether or not humans are likely to have caused recent climate responses, and even more important, (ii) will humans likely cause further and more rapid changes to our global climate system. If one looks at the conglomeration of evidence, it appears Christy in the minority with answering the former question and judging from other statements he has made, the same is true of the latter.
In the IPCC AR4 WGI, the scientific consensus of the modeling work completed, concluded the following:
"Climate simulations are consistent in showing that the global mean warming observed since 1970 can only be reproduced when models are forced with combinations of external forcings that include anthropogenic forcings (Figure 9.5). This conclusion holds despite a variety of different anthropogenic forcings and processes being included in these models (e.g., Tett et al., 2002; Broccoli et al., 2003; Meehl et al., 2004; Knutson et al., 2006). In all cases, the response to forcing from well-mixed greenhouse gases dominates the anthropogenic warming in the model. No climate model using natural forcings alone has reproduced the observed global warming trend in the second half of the 20th century. Therefore, modelling studies suggest that late 20th-century warming is much more likely to be anthropogenic than natural in origin, a finding which is confirmed by studies relying on formal detection and attribution methods"
Even further, through the use of detection and attribution studies, the IPCC said:
"The detection of an anthropogenic signal is also robust to using different methods. For example, Bayesian detection analyses (Appendix 9.A.2) robustly detect anthropogenic influence on near-surface temperature changes (Smith et al., 2003; Schnur and Hasselmann, 2005; Min and Hense, 2006a,b). In these studies, Bayes Factors (ratios of posterior to prior odds) are used to assess evidence supporting competing hypotheses (Kass and Raftery, 1995; see Appendix 9.A.2). A Bayesian analysis of seven climate models (Schnur and Hasselman, 2005) and Bayesian analyses of MMD 20C3M simulations (Min and Hense, 2006a,b) find decisive evidence for the influence of anthropogenic forcings. Lee et al. (2005), using an approach suggested by Berliner et al. (2000), evaluate the evidence for the presence of the combined greenhouse gas and sulphate aerosol (GS) signal, estimated from CGCM1 and CGCM2 (Table 8.1; McAvaney et al., 2001), in observations for several five-decade windows, beginning with 1900 to 1949 and ending with 1950 to 1999."
Scientists have also documented the human fingerprint on the type of warming happening as being consistent with what would be expected by an increased greenhouse effect, not solar or internal heat exchange. The "It's Not Us" argument becomes very unlikely when we look at observed diurnal temperature range, stratospheric temperature change, tropopause height, upper atmosphere cooling and contracting, ocean heat content, and sea level pressure.
All of this has led to one of the main conclusions of the conservative consensus of the IPCC:
"Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."
Dr. John Christy did not produce any work of significant merit or abundance, or highlight anyone else's, to refute these basic findings on multiple lines of evidence, through differing methodologies, of the human influence on the global temperature change. It is unequivocal that the climate is changing and it very likely our own doing. Because of this, we will likely harm ourselves. Fortunately, the future consequences are very likely up to us. These are statements of probability based on the best available human knowledge, and not a case of scientists jumping to conclusions, as Christy opines.
I'll end with a comment also said at the Congressional hearing:
"...[B]eware those who deride predictive science in its entirety, for they are also making a prediction: that we have nothing to worry about. And above all, do not shoot the messenger, for this is the coward’s way out of openly and honestly confronting the problem."
- Dr. Kerry A. Emanuel
Posted by grypo on Sunday, 10 April, 2011
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