By Nir J. Shaviv (D.Sc.)
On Sunday last week, a global warming debate was held at the Hebrew University, in front of a large public audience. The speakers included myself, and Prof. Nathan Paldor from the HU, on the so called sceptic side, and Prof. Dan Yakir (Weizmann) and Prof. Colin Price (Tel-Aviv Univ.) on the anthropogenic greenhouse gas (AGHG) side...
Although it was called a debate, it wasn't really one. It included 4 short presentations (about 12 mins each + 3 min for clarifying questions) and then another 45 mins of questions from the audience.
In my short presentations, I stressed a few major issues. First, there are no fingerprints proving that 20th century warming is necessarily human. Second, once you check the details, you find that there are notable inconsistencies. In particular, the AGHG theory predicts warming over the whole troposphere, while in reality, only the ground appears to have warmed over the past few decades, and that Earth's climate response to volcanic eruptions is significantly smaller than predicted by computer models. This is because these models tend to have an exaggerated climate sensitivity. Third, the only reason we can attribute the warming to humans, is because allegedly there is nothing else to blame, but there is, the increasing activity of the sun. And then I quickly showed some of the evidence showing that the sun affects climate through the cosmic ray climate link.
The second speaker was Prof. Dan Yakir. He started by saying that there is really no place or need to hold such debates anymore since the vast majority of scientists believe that the warming is anthropogenic. He mentioned Gore's nobel prize (yes, committees are to decide about scientific truths), Oreskes findings that from a 1000 papers, none contradict anthropogenic global warming, etc. He then attempted to debunk the cosmic ray - climate theory, some of his claims were supposed inconsistencies in the theory, and some were simply non-scientific arguments. Since I was not given a chance to address these claims, the response to each and every point raised can be found below.
The third speaker was Prof. Nathan Paldor. He emphasized the large uncertainties in our current understanding of climate systems. One such example was that of global dimming. Because of these large uncertainties, computer based modeling of 20th century warming or predictions of future climate change is mostly pointless at this time. He mentioned the 70's during which scientists urged Nixon to prepare the US for the upcoming ice-age, especially considering that the Soviets are better prepared for it!
The fourth speaker was Prof. Price, who emphasized the agreements between computer model predictions of AGHG theory and the observations. He showed, for example, that computer models trying to model 20th warming with only natural radiative forcings cannot explain the observed temperature trend, and models with anthropogenic contributions added, can explain. He then continued by trying to debunk the cosmic-ray climate theory. He mentioned several inconsistencies in the cosmic ray climate link (at least so he supposed). He also showed that for the cosmic ray climate mechanism to work, it rests on many links, some of which he doubted.
Before addressing the critiques, let me add that neither Yakir nor Price brought any evidence proving the standard anthropogenic scenario. Yakir did not attempt to prove anything (there is no need since the majority of scientists anyway support it), and Price did bring supporting evidence, but evidence that in reality does not prove anything about the validity of the AGHG theory.
The main claim raised by Price was that when computer models are used to fit 20th century warming, they do a very lousy job if you include all the natural forcing only, but they do a wonderful job if you include the anthropogenic forcing as well. This supposedly implies that one needs the large anthropogenic contribution to explain the warming. The key point here is that the natural forcings included all the known forcings, and not the unknown forcings, or specifically, the large indirect solar/climate link which these models fail to include, because the modelers bluntly neglect this mechanism. More about it here.
Although Yakir and Price did have a chance to address the critiques I raised about the AGHG (unlike the opposite), they chose not to.
Much more here -- including lots of lovely graphs.
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