General warming will create cooling in some areas due to changes in weather patterns caused by shifts in the jet stream and ocean currents.

If the Gulf stream continues to slow due to dilution of the sea waters by the melting ice pack at its northern subduction zone, northern Europe will cool as a result.

While it is true that warming and cooling have occurred throughout history with carbon dioxide levels following those temperature swings, it is the rate of increase that points to other than natural causes.

One scenario not much publicized involves the methane ice at the bottom of the deep oceans. It will take only a small rise in deep ocean temperature to cause this methane to be released adding significantly to the greenhouse gas levels.

It is just such releases that are theorized to be at the root of the Bermuda Triangle ship sinkings and aircraft disappearances. (The bubbles released cause ships to lose bouancy and methane in the air intake of aircraft engines has been shown to stall them even in very low concentrations.)

Digg user M0b1u5 writes:

The IPCC hockey stick has been well and truly debunked numerous times. They still keep using it. Bad data and worse analysis does not make a convincing case. Buried as inaccurate.

First of all, the MBH98 construction (”hockey stick graph”) is not proprietary of the IPCC. It does feature prominently in the AR4 report. Secondly, it has not been “well and truly debunked” even once.

MBH stands for Mann, Bradley, and Hughes, the authors of the study which produced this graph of temperature/composition data. Their methods focused on records from coral, the ice cores, and tree rings in addition to the contemporary instrumental record. While the MBH study has been constructively criticised on methodological and statistical grounds, never has it been “debunked.”

One of the studies most critical of MBH98 was conducted by Stephen McIntyre (a consultant to the minerals industry) and Ross McKitrick (an economist). Their biggest criticism of MBH98 was that it exaggerated 20th Century warming by using data sets which suppressed climatic variations over the past 1000 years, specifically the “Medieval Warm Period” and the later “Little Ice Age.”

The US Congress commissioned evaluations of MBH98 based largely on the McInture/McKitrick paper. One evaluation conducted by the National Research Council found that, while there were problems with the methodology used by Mann et al., the overall aberrations resulting from these uncertainties were “small in effect.”

The other major study into MBH was commissioned by Representative Joe Barton (R), an outspoken global warming skeptic. Conducted by the Committee on Energy and Commerce (red flag?) and known as the “Wegman Report,” this report supported the M/M paper from a statistical angle. However, the Wegman Report has been criticized in that it was never subject to formal peer review; that studies employing different methodologies from those used in MBH98 produced similar results; and that fixing the errors alleged by the Wegman Report did not produce markedly different results.

The IPCC would hardly place such great value in MBH98 if it were the only study of its kind. The IPCC is, after all, not a research body but a reviewing body. Numerous studies based on similar data and on computer models of varying configurations have, to varying extents, confirmed its findings.

There is certainly room for constructive criticism of MBH98, and future IPCC reports and studies by other organizations will likely improve upon the methodologies involved in such studies. But to claim that MBH98 has been debunked is to invoke polemics inconsistent with the scientific consensus and inconsistent even with critical statements from dissenters. To call MBH98 “bad data” without further qualification is, at best, a bit obtuse. As to the quality of analysis, well, that’s up in the air. Constructive criticism is certainly welcome.

User MacGregor writes:

Civilizations have risen and fallen for thousands of years due to climate change. No need to sacrifice the virgin because we don’t recognize this. Mars is having a climate change right now also. It’s not us.

This is an awfully stoic viewpoint, founded on what I would consider a straw man argument that is itself without historical basis. Civilizations have risen and fallen for thousands of years, but to what extent did “climate change” play a role in any of these scenarios? Misallocation of resources, warfare, and disease are more persistent culprits in civilizational collapses. Climate change almost certainly played a role in species extinction in the past, but we’re discussing the potentials of human-accelerated or aggravated climate change on a much shorter timescale.

The idea that Mars is experiencing “climate change” that parallels that potentially occurring on Earth is increasingly widespread but unfounded. This argument is based on observations of instability in the southern polar cap; this instability is well-documented and is known to fluctuate in a much more volatile way than we observe on Earth. The implication of this argument is that this polar instability is a new discovery; it is not, and it is associated with regional climate peculiarities that are endemic to Mars and without a clear analogy on Earth. See this article at RealClimate.org.

User Newbee70 had this crypticism to offer:

Still claiming global warming with Fantasy Science. The Alarmists will not admit their crying wolf; they can’t afford to keep losing the arguments: first global cooling; now global warming.

This is a faulty analogy and a possible case of post hoc ergo propter hoc. Global cooling was indeed a major concern in the press through the 1970s, but never had a scientific consensus behind it to rival those which support theories of human-accelerated global warming. Furthermore, there have been major improvements in climatological methodologies and understanding since the 1970s. It is true that the sensationalist fanfare in the press which surrounded global cooling provide a valuable caveat which is applicable to global warming, in that press depictions of global warming science are generally absent of the predicating precautions which are present in scientific reporting on the subject. Concern over global warming is centered on its manifestations in future centuries; the global cooling “scare” was associated with faulty datasets taken out of context, specific to the period from roughly 1945-1970.

User magicjava posted a thorough set of denunciations of the IPCC reports and methodologies. Some of this is constructive criticism, and some of it is polemical lambasting. It is essential to recognize the uncertainties and discontinuities in research methods behind such documentation as the IPCC AR4, and to recognize that the politicization of science is certainly not limited to either side of the debate. But regurgitating dissenting opinions does not transform them into the representation of a credible majority—all available evidence indicates that global warming skeptics remain a small minority in the scientific community at large.