Links. Tyler Cowen edition: global warming, economics exam, manure.
1) On the Marginal Revolution blog, Tyler Cowen links to this post about global warming. The denialist reactions to this link inspired me to tinker a bit with a graph from this post. As far as I can gauge, the hypothesis that medium run global temperatures are well described by a symmetrical thin tailed distribution with an upward shifting mean seems pretty plausible, the only real problem is, roughly, the second part of the 1930’s. I.e.: yes, global warming was and still is real (technical detail: the red and the green line connect highest highs and highest lows, the pink line divides the resulting space in two roughly equal parts, taking account of the 1930’s anomaly, this is inspired by Kuznets ‘freehand regression‘ method). Before I forget: global warming is heating up. 
2) He also links to a 1953 Harvard economics exam. And Krugman is right. When you read the exam you will concede that, nowadays, we are indeed living in dark ages of macro-economics and have forgotten a lot. Especially about the fact that much of macro-economics is about the flow of money and spending and monetary relations like wages, profits, interest rates and the like. And economics should, like this exam and as Peter Radford argues, about economies, not about ‘economics’ itself. 3) He also links to a book about the value of manure. More about this totally important subject (before 1900, and even afterwards, manure influenced the fate of regions and maybe even nations in a decisive way…) here.
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Real-World Economics Review Blog 
On the anomaly, an interesting hypothesis to test should be 2nd world war (but also for the first one).
As the articles in the May 30, 2008 issues of Nature explain:
http://www.nature.com/nature/journal/v453/n7195/full/nature06982.html
and
http://www.nature.com/news/2008/080528/full/453569a.html
Climate anomaly is an artefact
Glitch in the twentieth-century climate record is explained.
Quirin Schiermeier
The humble bucket turns out to be at the bottom of a perplexing anomaly in the climate records for the twentieth century.
The time series of land and ocean temperature measurements, begun in 1860, shows a strange cooling of about 0.3 °C in the global mean temperature in 1945, relative to the 1961–90 average. The sharpness of the drop stands out even more if the signatures of internal climate variability, such as those associated with El Niño events, are filtered from the record.
This cooling at the end of the Second World War is one of several temperature drops in the record. But unlike others, such as the 1991 cooling caused by the eruption of Mount Pinatubo in the Philippines, it is limited to ocean temperatures and is not associated with any known climatic or geological phenomenon. The nuclear explosions in 1945 over Hiroshima and Nagasaki were ruled out as a possible cause because they are thought to have had no impact on global temperature. Other theories proposed as explanations for the cooling include a massive 1940s El Niño event that had somehow slipped attention, or that it was the result of sulphate aerosols from burning dirty coal. But neither of these was convincing.
A US–British team of climate scientists has now found a surprisingly simple explanation for the long-standing conundrum (page 646). It turns out that the mysterious drop is due to differences in the way that British and US ships’ crews measured the sea surface temperature (SST) in the 1940s.
Only a few SST measurements were made during wartime, and almost exclusively by US ships. Then, in the summer of 1945, British ships resumed measurements. But whereas US crews had measured the temperature of the intake water used for cooling the ships’ engines, British crews collected water in buckets from the sea for their measurements. When these uninsulated buckets were hauled from the ocean, the temperature probe would get a little colder as a result of the cooling effect of evaporation. US measurements, on the other hand, yielded slightly higher temperatures due to the warm engine-room environment.
The standard logbook entries made at the time contain no information about how the measurements were taken, so the cause was overlooked, says David Thompson, first author on the paper and an atmospheric scientist at Colorado State University in Fort Collins. As a result, the bias — which, although small, was large enough to produce the sharp drop in global mean temperature — was never adjusted for.
“The time series is one of the great climate records we have,” Thompson says. “During a sabbatical in Britain, I revisited work that I had started a long time ago, and it suddenly occurred to me that the mid-1940s cooling might not necessarily have physical causes.”
Thompson discovered the explanation after questioning maritime experts from different countries about the history of shipping, and searching the scientific literature and international databases for scattered bits of relevant information.
“We always thought the observed cooling was real,” says Phil Jones, a climate researcher at the University of East Anglia, Norwich, UK, who carried out the study with Thompson. “We did know that there were fewer measurements during the war than before and thereafter, but we simply made wrong assumptions on how and by whom the measurements were taken,” he says. “It is pretty clear now that the bias is instrumental.”
It is welcome news for climate modellers. The post-war temperature anomaly has been grossly outside the range of all computer-based climate reconstructions considered by the Intergovernmental Panel on Climate Change (IPCC), and it was prominently featured in the group’s 2007 summary for policy-makers.
“The unusual up and down in SSTs in the 1940s stood out like a sore thumb in the past,” says Susan Solomon, a senior scientist at the US National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, and co-chair of the IPCC working group on the physical basis of climate change. “We couldn’t explain it, so we showed all the fingers, sore thumb and all,” she says.