http://dailycaller.com/2017/11/29/study-satellites-show-no-acceleration-in-global-warming-for-23-years/
Thanks for that, Slobodan. Here's an extract from the article which I think gets to the crux of the matter.
"Two major volcanoes — El Chichon in 1982 and Pinatubo in 1991 — caused global average temperature to dip as a result of volcanic ash, soot and debris reflecting sunlight back into space.
Those eruptions meant there was more subsequent warming in the following years, making the rate of warming appear to be rising as a result of man-made emissions or other factors, Christy said.
While volcanic eruptions are natural events, it was the timing of these that had such a noticeable effect on the trend. If the same eruptions had happened near the more recent end of the dataset, they could have pushed the overall trend into negative numbers, or a long-term cooling,” Christy said."It's clear from the historical and geological record that certain regions of the planet have undergone warming and cooling trends in the recent past, during this period we could call the 'Anthropocene'.
For example, it was rather cold during the Iron Age, from around 900 BC to 300 BC; then it was rather warm during the period in which the Roman Empire flourished, from around 250 BC to 400 AD; then it was rather cold again during the period known as the Dark Ages, which were really miserable.
The Medieval Warm Period started around 900 AD and resulted in favourable conditions in Greenland for the migration of the Vikings from Iceland. However, those warm conditions in Greenland began to change around 1300 AD putting great stress on agriculture and causing the Vikings to abandon their home, (although it probably wasn't the only cause. There are always numerous contributing causes to just about everything.)
The Medieval Warm Period was followed by the Little Ice Age, broadly from around 1350 AD to 1850 AD.
However, all these sucessively warm and cool periods are not consistently warm or cool during the whole period. There are often variations within each period. The Little Ice Age appears to have had at least 3 short, particularly cold periods within the longer, generally cold period. According to the NASA Earth Observatory, one began about 1650, another about 1770, and the last in 1850, all separated by intervals of slight or relative warming.
Our current warm period, often estimated as a rise of approximately 1 degree C during the past 150 years, is in relation to this particularly cold period which began in 1850 and peaked around 1910. The following NOAA temperature graph shows a global warming of 0.95 degrees C since the year 1870 which is already within (at least the beginning of) this particularly cold period, so one might reasonably ask why is the year 1870 considered to be an ideal and natural temperature which is representative of the baseline in the graph, ie. 0 degrees C.
If the base line is taken as the year 1910, one could claim the temperature has risen 1.4 degrees C in the past 100 years, which is more alarming than 0.95 degrees C during the past 146 years. If one uses the base line of 1944 as zero, the temperature rise becomes 0.65 degrees C during the past 72 years, and during the period of the most significant emissions of CO2 when industrialization and the world population really took off.
The reason why the year 1870 is chosen as the base line is because this is the period when the thermometer was developed as a reliable instrument, and instrumental temperature records began.
Imagine if we had reasonably accurate instrumental records going back a thousand years or more. Depending on which year or decade was chosen as a base line one could probably describe our current decade as representative of a significant warming, or a slight warming, or an insignificant warming, or zero warming, or a slight cooling.
This is the problem that "hockeystick' Michael Mann faced. He didn't of course have any instrumental records of global temperatures around a thousand years ago, during the Medieval Warm Period, nor sufficient proxy records such as tree rings, fossil pollen, corals, lake and ocean sediments, covering a global scale, in order to assess global average temperatures, so to produce a graph which mixed up modern 19th and 20th century instrumental records with a complete lack of instrumental data during the Medieval Warm Period, to show that the MWP didn't exist at a global level, was considered by certain less biased and more honest scientists to be scientific fraud.
Another part of the problem is that global changes in climate are never completely synchronous. The timing of the MWP and the LIA that occurred in Europe and the North West generally, would not have been identical with similar warming and cooling periods in China, or New Zealand, but there would have been an overlap, as recent studies show, so these events can be considered global.
An average global temperature is a human construct. It doesn't apply to any specific region, except by chance. According to the global map below, again from NOAA, there are actually regions on the planet that have shown no warming during the past century. There are other larger regions which have shown only very slight warming, of less than 1 degree F (not C).
There are even larger regions for which there is no data, specifically, but not only, around the polar regions. In fact, if we add the regions for which there is no data to the regions where there is no warming, to the regions where there is only very slight warming, that covers the majority of the surface of the planet.
Hope you can all now sleep soundly in the knowledge of the certainty.....of the uncertainty about climate change.