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Two papers published this week by the American Geophysical Union once again indicate that the science of climate change remains exceedingly uncertain. More significantly, the models that try to predict the future of the Earth’s climate continue to appear unreliable, with such large margins of error that it is at this time foolish to make any policy based on their predictions.
The first paper took a close look at the deep water currents in the Atlantic to see if it could track changes to what the authors’ call the Atlantic meridional overturning circulation (AMOC), more generally referred to as the Atlantic conveyor belt. This conveyor belt begins with the sinking of salty dense water in the northeast Atlantic off of Europe and Africa. The deep water current then travels south and into the Indian and Pacific Oceans where it comes to the surface only to flow back to the Atlantic, traveling north along the coast of North America as the Gulf Stream, bringing with it the warm temperatures that make Europe’s climate much warmer than its latitude would normally suggest.
According to most global warming models, higher temperatures should cause the glaciers in the Arctic and Greenland to melt, thereby pouring an increased amount of fresh water into the North Atlantic. This infusion of fresh water is then expected to lower the salinity and density of the Atlantic water, thus preventing it from sinking and thus acting to slow the conveyor belt, and possibly even causing it to shut down. The consequence would be no more Gulf Stream to warm the climate of Europe.
In other words: Disaster! Death! Destruction! All caused by global warming!
Unfortunately for these global warming models, the paper above found no trend at all. The conveyor belt is not slowing, as predicted. To quote the paper’s abstract:
Concerning the debate about whether a slowdown of Atlantic meredional overturning circulation has already occurred under global warming, the observed North Brazil Current transport time series suggests strong multidecadal variability but no significant trend.
And from the paper’s conclusion:
A slowdown of the AMOC has been reported from analysis of 5 hydrographic sections over the past 50 years and, while those results are controversial because of the limited data on which they are based, almost all state‐of‐the‐art climate models project significant slowdown of the AMOC during this century in response to the increased greenhouse gas concentrations in the atmosphere. Our results on the other hand suggest that such an anticipated slowdown has not occurred yet even though global temperatures have been significantly higher since the 1970s. While the AMOC might have been weakened from the 1960s to the early 1970s, it has been strengthening since then to the end of last century as shown in our transport time series. [emphasis mine]
Obviously, the science here is not “settled,” no matter how many times Al Gore says it.
The second paper took a look at 20 different IPCC climate models that tried to predict the long term precipitation changes for the Murray-Darling Basin of southeast Australia. Sadly, they also found that none of the models were very good a predicting those changes. To quote the paper:
Of those, the IPSL‐CM4 model was ranked the best for precipitation. We used the difference‐variance framework to investigate the P annual time series in the (single) IPSL‐CM4 model run in considerable detail. We found that this particular time series was not very convincing. . . . We believe that there is, at least at the moment, some reason to be cautious about overinterpreting the results from single runs of a climate model. [emphasis mine]
These results do not reject the possibility of global warming. All they show is that the Earth’s climate is an extremely complicated thing, and that at present the data available does not yet explain fully that climate’s behavior. More importantly, the computer models that scientists have created to try to simulate this climate still do a very poor job of predicting what that climate will do.
We must therefore treat their pronouncements of doom with great skepticism.