[Vision2020] global mean temperature

[Donovan Arnold]

Paul,
 
I wonder, how accurate were temperature readings back in the 1700s?
 
If global warming only increases the mean world temperature by about 1 or 2 degrees a century, can we claim that the technology of the 1700s had a margin of error in recording temperature within that range? 
 
I would tend to think that other means of measurement would be more reliable, such as ice core samples and tree rings. 
 
Donovan Arnold

--- On Tue, 10/20/09, Paul Rumelhart <godshatter at yahoo.com> wrote:


From: Paul Rumelhart <godshatter at yahoo.com>
Subject: [Vision2020] global mean temperature
To: "Vision2020" <vision2020 at moscow.com>
Date: Tuesday, October 20, 2009, 4:31 AM


After some earlier discussion on global warming, I scanned the web looking for graphs of global temperature.  I found several, but nothing really good.  So, since I was in need of yet another life-draining outside-of-work project, I decided I'd go find the data and run some analyses on it myself..

I found a dataset from the National Climatic Data Center, part of the National Oceanic and Atmospheric Administration.  The data files I used are located here: ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/v2/

I used the "adjusted" datasets, which have stripped known bad data.

So, a little c programming (and not a few Mountain Dews) later, I had a graph of global mean temperature.  The  datasets I started with are averaged for each month, some data going back to the early 1700's.  I took the monthly values, multiplied them by the number of days per month, averaged them out for the year, and averaged the data from all the global temperature stations (many hundreds or even thousands of them - I haven't counted them) and produced a nice graph that shows the data for years 1970 through 2009 (attached).

I expected something more straightforward, what I got was an enigma.  I see a rise in temperature in 1989 - 1993, a slightly smaller peak around 1998, and a severe temperature drop in 2006, which returns almost to it's previous temperature by 2009.  Obviously, 2009 is not finished, so that data point will probably change.

I otherwise see a gentle sloping upwards over the course of the last few decades.  This presumably reflects the presumed global warming and is part of what is used to predict future temperature.  I'm looking forward to reading up on methodologies used for determining global mean temperature, and what sophisticated statistics they use to get there.  It's been 20 years since my last statistics course.

Once my program becomes a little more sophisticated, I'm going to plot Moscow's weather vs. the global mean, since the U of I has data in the file going back (iirc) to 1893.  I'm also going to plot min and max annual temperatures, and plot the monthly values close up around 2006 to see what happened.

So, what happen in or around 1991, 1998, and 2006?  I'm wondering if 2006 was affected by La Nina or a volcano eruption or something.  I'm going to plot each month's values per year around that time period too, to see if I can find out if there's some bad data lurking in the file somewhere or if it's consistent.

Anyway, a work in progress.

Paul

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