JANUARY 1790 The average or medium temperature of this month was 44 degrees This is the mildest month of January on record. Fogs prevailed very much in the morning but a hot sun soon dispersed them and the mercury often ran up to 70 in the shade at mid day. Boys were often seen swimming in the Delaware and Schuylkill rivers. There were frequent showers as in April some of which were accompanied by thunder and lightning The uncommon mildness of the weather continued until the 7th of February.
Compare that to January, 2009 with an average temperature of 27F, 17 degrees cooler than 1790. One month of course is not indicative of the climate, so let us look at the 30 year period from 1790-1819 and compare that to the last 10 “hot” years.
According to several of the most widely quoted climate scientists in the world, winters were much colder 200 years ago than now - yet the boys swimming in the Delaware in January, 1790 apparently were unaware.
Another interesting fact which can be derived from Charles Pierce’s data, is that January temperatures cooled dramatically during the period 1790-1819 - as can be seen in the graph below. The cooling rate was 13F/century. What could have caused this cooling? We are told by some experts that variations in solar activity can only affect the earth’s temperature by a few tenths of a degree. CO2 levels had been rising since the start of the industrial age. The downward trend is fairly linear and does not show any sharp downward spikes, so it is unlikely to be due to volcanic activity. What other “natural variability” could have caused such a dramatic drop in temperature?