Unprecedented? – Part 2
As explained in the article “The rise and fall of the Hockey Stick” a central and critical plank of the alarmist global warming case is that the current phase of warming is unprecedented. One aspect of proving that the warming of the last three decades has been unusual and unique, and therefore unnatural, has been to try to prove that recent temperatures have been higher than in the recent past and the article “Unprecedented?” explained how this required that the Medieval Warm Period be eliminated from the climate history.
The other argument that the the climate alarmist have put forward to try to show that the recent temperature record has been unusual has been to argue that the rate of change of temperature in recent decades has been anomalous.
Since the the current warming started it has occurred in two distinct phases. The first period of warming that started around 1900 lasted up until around 1950, there was then a period of about 30 years when temperatures dropped back a bit and then around 1975 the most recent period of warming started.
The bulk of CO2 added to the atmosphere by human activity has been added since the end of the World War 2. Those who support the claim that CO2 is responsible for all the recent warming do not argue that the warming in the first half of the 20th was caused by CO2. Therefore it should be possible to compare the rate of change of temperatures in the first half of the 20th Century, which everyone agrees was natural, with the rate of change in the second half of the 20th Century, which some claim is not natural, and see if there is a difference between the two.
Below are two graphs that both show temperature changes over a 51 year period. Both use exactly the same format for displaying the data. One chart shows the period 1885 to 1946 and the other chart shows the period 1957-2008. One, it is agreed by everyone, is caused by nature and one, it is claimed by some, is unnatural. Can you tell which is which?
The answer is that the chart on the left is for 1957 – 2008 and is considered by the climate alarmists to show unprecedented warming. What do you think?