The public might not understand the science, but they do understand cheating
Dr. David Evans
6 October 2010
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They Don’t Tell You: The Current Global Warming Trend is Over 300 Years Old
Satellite data only goes back to 1979, and global land-thermometer records only go back to 1850. Before that we have to resort to “proxies”, which are various natural phenomena from which temperature can be deduced. As we go further back in time, the errors and uncertainties increase.
Here is a best estimate of the global air temperature for the last 2,000 years, using the best available source for each period:
- 1979 – Now: Satellite data (UAH, as per Figure 14).
- 1850 – 1979: Land thermometer record (HadCrut3, from the UK Met Office Hadley Centre and the Climatic Research Unit, slightly less tricked up than the GISS data of Figure 13).
- 16 AD – 1850: Loehle’s reconstruction in 2007 based on all temperature proxies except tree rings. It used 18 proxies over a wide geographical range, including sediments, boreholes, pollen, oxygen-18, stalagmites, magnesium to calcium ratios, algae, and cave formation. First reconstruction in which every proxy was calibrated to temperature in a peer reviewed article; arguably about as good as it gets. (Tree rings make poor proxies: Tree growth depends heavily on water and mineral availability so it is often not proportional to temperature as assumed, tree populations genetically adapt to climate change so long term climate trends fade out, and individual trees respond differently to temperature so the choice of which individual trees to examine introduces subjectivity and bias. See page 1050.) (A second high quality reconstruction, with 30 proxies including six tree rings, but no bristlecone pines, was made by Ljungqvist in 2010. It basically confirms Loehle’s results, estimates the current air temperature as about 0.1°C less than its medieval peak in 950 AD, and confirms the start date of the current global warming as just before 1700.)
(Technical note: The three data sources are spliced together by simply resetting their anomaly origins so that the average of overlapping periods are equal. The annualized satellite and the land-thermometer data was smoothed with a five year filter. To avoid a discontinuity moving from land-thermometer to satellite data, the land-thermometer temperature was used for 1979, and the midpoints between the land-thermometer and satellite temperatures were used for 1980 and 1981.)
The land thermometer records exaggerate the rate of warming using the tricks documented in parts 1 and 2 of this series, but they are the best data we have for 1850 – 1979. However we need a rough idea of historical temperatures in that period to make several crucial points, so we will go with that data.
The current global warming trend started before 1700, some 310 years ago. That was pre-industrial, so a natural climate force must have started the current global warming trend.
That the medieval warm period existed is well documented in European history. That it was worldwide is verified by hundreds of peer-reviewed studies, by over 700 scientists from over 400 separate research institutions, most of whom found that the period was probably warmer than today. The studies are from all over the world (except Australia)—here is a stunning illustration that makes that point.
Likewise the little ice age is well documented in European history. It forced an end to the Viking colonization of Greenland in about 1430, the Thames River in London froze over most winters but the last time it froze was 1804, and in the 1600s and 1700s animals in Europe would die of cold inside barns which never happens now. Like the medieval warm period, temperature proxies around the world confirm that it was worldwide.
This temperature picture here broadly agrees with what the climate establishment believed until 1996:
They Don’t Tell You: Global Warming Alternates With Global Cooling Within the Trend
If we zoom in on just after 1850 (when the thermometer data starts—proxies are too imprecise to determine turning points), we can see an interesting pattern:
If the pattern continues, the next 12 – 35 years will see cooling.
How many in the public or the political class are aware of this pattern? Everyone has heard the climate establishment’s forecast that the strong warming of the last three decades will continue while we continue emitting CO2. But the establishment do not tell people that some or all of that strong warming since 1975 is due to a cyclic phenomenon that is now entering a cooling phase.
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