To: Bill who wrote (883810 ) 8/31/2015 1:26:26 PM From: Wharf Rat Respond to Where the globe is cooling due to global warmingAugust 31, 2015 Uncategorized dcraig Thanks to Mr. Robert Baker, a man of deep integrity, loyalty and incredible decency, for this one. thermohaline circulation system (THC). I had never heard of it and had to keep repeating it in my mind so I wouldn’t forget it. Thermo (heat) and haline (salt). Thermohaline.RealClimate. Climate science from climate scientists. And this latest study is from them. “The North Atlantic between Newfoundland and Ireland is practically the only region of the world that has defied global warming and even cooled. Last winter there even was the coldest on record – while globally it was the hottest on record. Our recent study (Rahmstorf et al. 2015) attributes this to a weakening of the Gulf Stream System, which is apparently unique in the last thousand years. “The whole world is warming. The whole world? No! A region in the subpolar Atlantic has cooled over the past century. So what’s so special about this region between Newfoundland and Ireland? “It happens to be just that area for which climate models predict a cooling when the Gulf Stream System weakens (experts speak of the Atlantic meridional overturning circulation or AMOC, as part of the global thermohaline circulation). That this might happen as a result of global warming is discussed in the scientific community since the 1980s – since Wally Broecker’s classical Nature article ‘ Unpleasant surprises in the greenhouse? ‘ Meanwhile evidence is mounting that the long-feared circulation decline is already well underway.” Wallace Broecker, by the way predicted global warming was coming way back in 1975 when he published an article in Science with this prescient title: “Climatic Change: Are We on the Brink of a Pronounced Global Warming?” VIDEO VIDEO “Climate models have long predicted such a slowdown – both the current 5th and the previous 4th IPCC report call a slowdown in this century “very likely”, which means at least 90% probability. When emissions continue unabated, the IPCC expects 12% to 54% decline by 2100. But the actual past evolution of the flow is difficult to reconstruct owing to the scarcity of direct measurements. Therefore, in our study we use data on sea surface temperatures in order to infer the strength of the flow: we use the temperature difference between the region most strongly influenced by the AMOC and the rest of the northern hemisphere.” “Now we are not the first to have inferred from temperature data that the flow must have weakened. “What is new is that we have used proxy reconstructions of large-scale surface temperature (Mann et al, 2009) previously published by one of us (study co-author and RealClimate co-founder Mike Mann) that extend back to 900 AD (see “What we can learn from studying the last millennium (or so)” ) to estimate the circulation (AMOC) intensity over the entire last 1100 years (Fig. 3). This shows that despite the substantial uncertainties in the proxy reconstruction, the weakness of the flow after 1975 is unique in more than a thousand years, with at least 99 per cent probability. This strongly suggests that the weak overturning is not due to natural variability but rather a result of global warming.” “Also in 2014 we again find a remarkable cold bubble over the northern Atlantic – as a look at the NASA website shows. 2014 was globally the warmest year on record, 1 °C warmer than the average for 1880-1920. But the subpolar Atlantic was 1-2 °C colder than that baseline. And even more recently, NOAA last week released the stunning temperature analysis for the past winter shown in Fig. 4. That winter was globally the warmest since records began in 1880. But in the subpolar North Atlantic, it was the coldest on record! That suggests the decline of the circulation has progressed even further now than we documented in the paper. “The consequences of a large reduction in ocean overturning would look nothing like the Hollywood film The Day After Tomorrow. But they would not be harmless either – e.g. for sea level (Levermann et al. 2005) particularly along the US east coast (Yin et al. 2009), marine ecosystems, fisheries and possibly even storminess in Europe (Woollings et al. 2012). We have studied these consequences some years ago in an interdisciplinary project with colleagues from Bremerhaven, Hamburg and Norway – the results are summarized in Kuhlbrodt et al. 2009. “If the circulation weakens too much it can even completely break down – the AMOC has a well-known ‘tipping point’ (Lenton et al., 2008). The latest IPCC report (just like the previous one) estimates a probability of up to 10% that this could happen as early as this century. However, this assessment is based on models that may underestimate the risk, as mentioned above. Expert surveys indicate that many researchers assess the risk higher than the (generally conservative) IPCC, as is the case for sea level. In a detailed survey (Kriegler et al 2009), the 16 experts interviewed saw already at moderate global warming (2-4 °C) a probability of a ‘tipping’ (major reorganisation) of the flow between 5 and 40 percent. With strong global warming (4-8 °C) this probability was even estimated as between 20 and 65 percent.” dcraig.blogs.redding.com
