Friday, August 24, 2007 ... Deutsch/Español/Related posts from blogosphere

Ivan Janković: Why climate change skeptics should applaud hockey stick?

The author has sent a screenshot of the visitor #1,500,000 but the actual visitor #1,500,000 was, according to the Sitemeter, from Bonn, Germany and came to the main page of this blog from a German physics website

Hockey stick graph from IPCC TAR 2001 is often cited as an important paleoclimatological piece of evidence of unprecedented climate change in 20th Century. Graph, showing flat temperature trend in most of previous millenium with sudden upward swing in the last Century, is widely advertised in schools, media, and by advocacy groups, as a reason to believe in man-made global warming. No surprise, many climate change realists or skeptics, on the other side, tend to reject this graph and underlying study as bogus and scientifically invalid. Well-known hockey stick scientific controversy in previous years was about how reliable are Mann et al. results in their 1998 and 1999 reconstruction(s) of North Hemispheric temperature variations in the past millenium. From the very beginning of the controversy, implicit for both sides involved was belief that to affirm hockey stick was to affirm human induced global warming in the last Century, and vice versa – in order to refute anthropogenic warming thesis you should refute hockey stick conclusions as well. As prof. David Deming has pointed out, probably the very motivation of alarmistis to "abolish Medieval warm period" was to make human induced climate change more intuitively acceptable as a concept; if MWP realy didn't exist, i.e. if current climate is by far warmest one in the past millenium, and if that warming occurred suddenly and anomalously in 20th Century, than it must be something more than ordinary natural variability at work, that "forces" climate to change so tremendously; most probably – human influence. Conversely, for skeptics, to abolish this "abolishing of MWP" would mean to vindicate their basic claim that in 20th Century climate there is not anything unusual or unprecedented, and thereby that human influence on global temperature is probably negligible.

But, problem with this whole debate was that it was wrong way rounded from its inception. Hockey stick results had nothing to do with attribution of 20th Century warming to anthropogenic causes at all. At the contrary, were those results correct, they would only demonstrate that NATURAL warming in 20th Century was unprecedented. Both sides were wrong in prevailing motivations for debate.

Let us take a closer look to the hockey stick reconstruction to better understand this. The reconstruction encompasses period since 1000 AD to 1980. Period of "unprecedented warming" which hockey stick refers to is the period 1900-1980 (reconstrucion stops in 1980, and some cynical explanations of that fact point to assumption that climate proxies from period after 1980 do not show much warming – so called "divergence problem" – so it was quite inconvinient for authors to include them in the study purporting to suggest human guilt for "unprecedented" warming in 20 th Century). By and large, according to IPCC, anthropogenic influence on global climate became dominant only in the second half of 20th Century. In other words, "mainstream" climatological analysis, including IPCC, considers warming before approximately 1950 to be dominantly caused by natural factors.

How this fits into the wider picture of hockey stick implications? The answer is pretty straightforward. We had a fluctuating temperature since 1900-1915, then from 1915-1945 fast global warming at rate 0.16 degrees C per decade (warming that must be, according to IPCC, dominantly due to the natural factors). And then from 1945-1976/77 we had a minor global cooling, whatever factors were principal drivers of global climate and temperature in that period. So, the only period of "unprecedented warming in 20 th Century" covered by Hockey stick reconstruction, is basically large NATURAL warming from 1915-1945. This reconstruction doesn't deal with period 1976 onwards which is the only period of warming that, according to the mainstream scientific assessment, must be, or at least should be, driven primarily by human influence!

Obvious conclusion from the above is that Hockey Stick reconstruction clearly attributes "unprecedented" warming in 20th Century to NATURAL CAUSES, and not to human ones (if one takes IPCC findings as paramount). So, we are left with following choice: either MWP was warmer than 20th Century natural warming, or 20 th Century naturally occuring warmth was warmer than MWP. In either case, there is not much "useful" implications for anthropogenic climate change thesis to be drawn from the Hockey stick reconstruction. In the Hockey stick context, anthropogenic warming simply doesn't play any significant role!

Let me be clear: I think this reconstruction is fatally flawed, as many scientists already have demonstrated. Most of the other reconstructions and historical evidence we have, strongly support thesis of Medieval warm period being significantly warmer then the present climate. But, the point is – even if we accept hockey stick analysis as correct, it only would prove that natural forces, driving temperature increase in the first part of 20th Century, were anomalously strong. And frankly, climate "skeptic" (person advocating thesis that present global warming is mostly of natural and not anthropogenic origin) has all reasons to be satisfied with such an outcome. The same natural forces causing climate to warm up so greatly in the first half of 20th Century probably are at work even now (whatever they are), and we have not much reason to believe in dubious greenhouse theories. Occam's razor cuts them off.

Add to Digg this Add to reddit

snail feedback (1) :

reader Angee said...

This issue has been the subject of arduous debates for more than 20 years. And most of the claims say that modern civilization is responsible for the higher atmospheric temperatures, which were caused by man-made greenhouse gases. The Inter-Governmental Panel on Climate Change (IPCC), active since 1988, is the main supporter of this thesis.

The carbon dioxide (CO2) is the main argument of the IPCC. Proud to convey the “consensus” of hundreds of top scientists from around the world, this organisation has hardly ever hesitated to confirm its belief in the Assessments Reports and their correctness.

The IPCC Report from 1990 states:

“Emission resulting from human activities is substantially increasing the atmospheric concentration of the greenhouse gases: carbon dioxide, methane, chlorofluorocarbons (CFCs) and nitrous oxide. These increases will enhance the greenhouse effect, resulting on average in additional warming of the earth’s surface. The main greenhouse gas, water vapour, will increase in response to global warming and further enhance it”.

Not everybody agrees with IPCC and its “consensus” thesis. While most of the scientists and climatologists support it, there are also voices which contradict the conclusions of IPCC. The most important document in this regard is the “Oregon Petition” of 1998, signed by 17,000 scientists who were protesting against the Kyoto Agreement. The petition requested the acknowledgement of the following statement:

There is no convincing scientific evidence that human release of carbon dioxide, methane, or other greenhouse gases is causing or will, in the foreseeable future, cause catastrophic heating of the Earth's atmosphere and disruption of the Earth's climate. Moreover, there is substantial scientific evidence that increases in atmospheric carbon dioxide produce many beneficial effects upon the natural plant and animal environments of the Earth”.

Neither the IPCC nor the Oregon Petition’s claims are satisfactory enough. They don’t reflect a correct assessment and analysis of the Earth’s climate during the last 150 years.

You can find here a graphof CO2 emissions: