Tamino describes the period since 1975 as the “period of modern warming” – implying that CO2 has altered the behaviour of the climate. But we can see in the HadCRUT Northern Hemisphere video above that the warming from 1910 to 1940 was nearly identical to the post 1975 trend. This in spite of the fact that CO2 levels were well below Hansen’s safe 350 ppm, and were rising very slowly.
This similarity in itself is enough to show that Hansen’s theories about 1980s warming are highly questionable.
The eventual warming for these gases added during the 1970s is about 0.2C if the climate sensitivity is near 2C for doubled C02, but almost 0.4C if the sensitivity is near 4C.
Therefore, although the observed warming in the 1970s (Figure 2-1) is consistent with the increased trace gas abundances, the changes cannot be confidently ascribed to the greenhouse effect. However, if the abundance of the greenhouse gases continue to increase with at least the rate of the 1970s, their impact on global temperature may soon begin to rise above the noise level. For such a rate of Climate Sensitivity to Increasing Greenhouse Gases increase the total warming at equilibrium due to gases added in the 1970s and 1980s would be about 0.5C, for a climate sensitivity of 3C.
Moreover, one would expect that for a 20 year period, a large part of the equilibrium warming would appear by the end of the period. This possible warming should be compared to the standard deviation of observed temperatures, which is about 0.15C for a 20 year period. This comparison is the basis for anticipating that significant warming is likely to occur by 1990
Now, let’s take this one step further. Earlier I discussed how older temperatures have been adjusted downwards, and recent temperatures have been adjusted upwards. This creates the effect of a rotation.
What happens if we rotate the shifted HadCrut graph in the opposite direction of the data manipulations?
Interesting!! The second half of the Hadley graph becomes a repeat of the first half.
It looks to me like the “period of modern warming” is primarily a combination of natural variability and highly questionable data manipulation.