The number
of weather stations recording very warm night - time temperatures and the frequency with which these occur has increased since the mid 1970s.
They wanted to better understand how the climate of the Alaska Range has changed over the past several hundred years, because
few weather station records of past climate in mountainous areas go back further than 1950.
The main basis for the claim that there has been «unusual» global warming since the late 19th century is that the global temperature estimates constructed from
weather station records suggest a warming trend of about 0.8 - 1.0 °C since about 1880.
In our papers
studying weather station records, we found that global temperatures have alternated between relatively cool and relatively warm periods roughly every 30/40 years since at least the late 19th century.
There's been a little discussion of a non-peer reviewed (so far) paper published by Anthony Watts et al. claiming the warming at the best - sited US weather stations is two - thirds» that estimated by NOAA for the US based on the entire
adjusted weather station record.
namely, that the average temperatures in the AWS record (post 1980) are warmer — by about 1 Deg C — than the pre-1980
manned weather station record.
This slide into cold is showing up in
German weather station records where the last 30 yrs of winter (DJF) are trending -19 dgC per 1000 yrs, much faster than the slow decline to normal glacials.
UAH from their satellite data are suggesting that this is a more accurate record than the global temperature records because of UHI not being properly allowed for in
urban weather stations records (supported by NASA 3 yr research on UHI).
They wanted to better understand how the climate of the Alaska Range has changed over the past several hundred years, because
few weather station records of past climate in mountainous areas go back further than 1950.
And years of painstaking temperature measurements from thousands
of weather station records, have confirmed a slow inexorable rise in that overall temperature across the globe.
The NASA Goddard Institute for Space Studies (NASA GISS) is one of the five groups that currently publish global temperature trend estimates
from weather station records, i.e., they produce one of the curves we showed you at the start of this essay in Figure 1.
The mean temperature change or the OHC increase is an integral over all of that and therefore can be estimated to higher precision than any individual reading (just like for
the weather station record).
So, initially, these estimates might seem to provide a useful comparison for
the weather station records.
However, as we will discuss in this essay, many of
the weather station records used for these estimates of global warming contain artificial warming biases, which are not representative of actual global temperatures.
The Climate Research Unit was one of the first groups to construct
a weather station record dataset in the 1980s, e.g., see Jones et al., 1986 (Open access).
So, this has led many people to conclude that the «unusual» global warming implied by
the weather station records is man - made global warming from our fossil fuel usage.
The main basis for the claim that there has been «unusual» global warming since the Industrial Revolution arises from the various global temperature estimates constructed from
weather station records.
Surely, there's got to be some other global warming indicator that shows a long - term global warming trend...» Remarkably, aside from
the weather station record estimates, almost all of the so - called «global warming indicators» are short - term estimates...
In other words, much of the «unusual global warming» is simply an artefact of urbanization bias in
the weather station records, i.e., not man - made global warming!
Aside from the problems urban heat islands can cause for city - dwellers, they also create an insidious problem for researchers who want to use
weather station records to estimate global temperature trends.
They decided to develop a computer program which would automatically search through
the weather station records and apply adjustments to remove any urbanization bias.
Indeed, many of the groups using
weather station records for estimating global temperature trends, also combine their estimates with the sea surface temperature records to construct «land - and - sea» global temperature estimates.
If you wanted to maintain
a weather station record you needed to have staff living near by who could take each day's measurements.
Unfortunately, many of
the weather station records used for these estimates are affected by urbanization bias.
This program is described by Menne & Williams, 2009 (Open access) and adjusts each of
the weather station records in their dataset so that it better matches those of its neighbours.
He believes that the claims of unusual late - 20th century global warming are mostly an artefact of biases in
the weather station records, e.g., urbanization bias.
A second study, published by Mark Risser and Michael Wehner at Lawrence Berkeley National Laboratory, performed a similar analysis of past
weather station records.
However the problem is not simple, and the bias problems present a very different challenge to
weather station records.
Evidence that the tendency was to round down is supported by the frequency of timeline temperature trends in many
weather station records to shift up as of metrication in 1972 (see mean, minima and maxima), a trend that could only occur if a majority of previous recordings were rounded down - unless Australia's weather coincidentally also warmed sharply and immediately as of 1972.
Temperature data were the focus of the so - called 2009 Climategate controversy, in which opponents of greenhouse gas regulation alleged that leaked emails from a British climate laboratory showed manipulation of
weather station records.
It lays out the allegations, notes that Jones admitted in an interview this year that the loss of
the weather station records was «not acceptable» (8), then leaves the issue hanging.