Sonntag, 26. Januar 2014

Global Temperature Graphs: Which is the right one? Part one.

Global Temperature Graphs: Which is the right one? Part one.

If you see discussions on global warming, one thing is always present: Temperature graphs in various shapes and colors, ready to proof the assumption of the presenter of an idea. But whom to believe? And how - as a non-scientist - to check if there is something wrong with the data?

One thing is to mention: Temperatures measured with instrument are available for about 250 years, but only from about 1850 there are enough to get a global picture. So official graphs start from this date or later.

A good way is to go to official sources and there are a number of graphs which are considered as sound. We will check later which one are most common.

If we want to compare various graphs of temperature or with other data like CO2 or sea ice, we need a tool to get the whole picture. One of the best and easiest to handle tools is In this tool all relevant data sets are already included, and you can make very impressive work with it. Note: This tool and the web site is neutral, not taking a certain stand in the climate warming discussion.

Just let's go straight to the website and check the most important temperature graphs:

Here we see three very common temperature graphs:

Red: HADCRUT 3 from Hadley Centre combining sea surface and land temperature (air temp 2 meters above surface)
Pink: Hadcrut trend over 160 years: 0.8°C, which is 0.5 per century and 0.05 per decade.

Green: HADSST 3: sea surface global temperature
Turquoise: HADSST 3 trend over 160 years: 0.65°C, which is 0.4 per century

Blue: CRUTEM3 only global land temperature
Brown: CRUTEM 3 trend over 160 years: 0.95°C, which is 0.6 per century

So why the differences?

Possible answers:
  • The ocean temperature is more stable in the long run, so changes are not so easy achieved.
  • Temperature stations on land often have been surrounded by cities or human-induced heat, which could have accelerated the recording of the blue CRUTEM curve.
  • Remote stations (with few human disturbance) have been abandoned, thus giving more weight to stations near towns.

If someone wishes to reduce human influences to temperature measurement, sea surface temperature cold be the choice for long-run observation, especially as the ocean surface is two third of the earth's surface.

If we take the average from land and sea, the HADCRUT, we have 0.6°C rise per century. Added this to the already started century, we would have a temperature 0.5°C higher than today, which would be no problem then.

So the question is: Is the global accelerating, or remaining, or declining?
This question we should look for at a later time. And it will be another chapter in the Layman's Climate Course

Now back to our Question: What is the right temperature curve?

The answer so far: Land and Sea surface temperature curves differ from each other. Land temperature seem to show human influence to the data, whereas sea surface data show a smoothed and delayed record. So the best seems to stick to the combined global data, which is also standard in science.

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