The info provided via the GHCN Temperature Plotter's Histogram tab is intended to help you understand what the data actually says.
There are so many options and configurations that using this can be a little confusing. (ok, extremely confusing.) The info on this page should help.
|Histogram options |
Full globe, unadjusted data, Baseline: 1961-1990
||Trend - Bin size = 0.01 - This is the long term trend (°C/decade) for each site
for the specified date range
||Baseline Temperature - Bin size = 1 - The average temperature of the planet is supposed to be
either 14°C or 15°C (depending on the reference)
||Latitude - Bin size = 10 - Notice that most of the data is from the Northern Hemisphere
||Longitude - Bin size = 10 - There are 3 peaks|
the Americas, Europe/Africa, China/Japan/Australia
|NumOfYrs - Bin size = 2 - Number of sites with the indicated number of years
- x-axis min/max set to 0-120
To save copies of these plots, simply right click the chart and select Save image as... or Copy image (the exact text depends on your browser). Chrome saves these as 180h x 360w *.png files.
|Effect of bin size |
USA 1900-2014 trend (°C/decade) - unadjusted data
There are 2 buttons that support comparing multiple datasets.
Raw vs Adjusted comparisons
The application provides 4 datasets
For this to work, both the raw (unadjusted) and associated adjusted data must be loaded. It does not matter which of the 2 related datasets are selected.
For a good comparison, make sure that the selection criteria are the same for both datasets - normally, you will want the same countries and/or same time periods. Since the number of sites is different, you may want to use the Raw vs Adj Filters tab to refine your selection.
|Comparison of adjusted and unadjusted data|
USA 1900-2014 trend (°C/decade)
From that graph, it should be obvious that a major part of the warming signal is produced by the data adjustment process - a process which is poorly documented and is very difficult to review. This particular graph suggests that a major part of the warming signal is produced by simply dropping those sites which are cooling. Of course, it is not that simple.
The ocean data is identical in the 2 associated datasets and provided as only an "anomaly" temperature - meaning that the actual ocean temperatures are NOT provided, only an offset from some unspecified "average" value. A general overview of that data, and an explanation of why I think it is mostly worthless, is provided here.
Comparison of different time periods
These plots use all of the default filters to get only the 523 stations with the longest records.
|Temperature Trend (°C/decade)|
1900-1960 (blue) and 1960-2014 (red)
|Global - unadjusted data, 523 stations||USA - unadjusted data, 328 stations|
||Global minus USA - unadjusted data, 195 stations
||Global minus USA - adjusted data, 187 stations
A better comparison might be a couple of 20 year periods - 1900-1920 vs 1990-2010. Using just the raw USA data with all the filters turned on shows no significant increase in warming. Because the spread of the data increased, the Trend bin size was set to 0.05 (the default is 0.01) to produce a smoother plot.
|USA Unadjusted Temperature Trends (°C/decade)
1900-1920 (blue) 1990-2010 (red)
Just for comparison, the next two plots use all 4561 adjusted global sites that meet the most basic baseline requirements. The first plot shows the trends from 1900 to 1960 - of the 4561 selected sites, 767 did not have enough data points to compute a trend, and several sites had trends larger than ±2°C/decade indicating obvious bad data. The trend histogram for the full 1900 to 2014 period is shown on the right for comparison.
|Global Adjusted data|
Of 4561 sites, 767 were not included due to insufficient data
Trends larger than ±2°C/decade indicate bad data
Trend from 1900 to 2014 uses all 4561 selected sites
One of my primary complaints with respect to climate reporting is a complete lack of information on the data spreads (standard deviations). Hopefully, this tool will bring some sanity to the discussion.
You will often hear that "the United States is not the entire planet", or something to that effect. However, it has the best long term temperature record and, no matter how you cut it, an average of more than 300 stations spread over an entire continent has to be a better proxy for world climate than 12 trees in Yamal. (According to the article, out of 252 Yamal specimens, 12 showed temperature increases, 34 showed warmer temperatures in the Middle Ages.)