The vast majority of the world’s high quality historical temperature data comes from the United States. NOAA has no long term daily temperature from most of the earth’s surface.
In 1999, NASA’s James Hansen was upset that the US temperature trend didn’t match the imaginary warming trend he had created for the rest of the world.
“in the U.S. there has been little temperature change in the past 50 years, the time of rapidly increasing greenhouse gases — in fact, there was a slight cooling throughout much of the country ….. climate trends have been fundamentally different in the U.S. than in the world as a whole.”
NASA GISS: Science Briefs: Whither U.S. Climate?
So NASA and NOAA did just what would expect them to, they altered the US temperature data to match the fake global temperature.
In 2005 the adjustments totaled 0.5F and tailed off after 1990.
The Time of Observation Bias adjustment totaled 0.3F and tailed off after 1995.
Now the adjustments are much larger.
The TOB adjustment has doubled in size and no longer tails off after 1990.
Here are the specifics of the current adjustments for maximum temperature.
I used a simple average of the data per year to generate these graphs. People have complained that the data needs to be gridded because of uneven distribution of stations, but the data doesn’t support that idea, NOAA temperature graphs are almost identical to the average of the final adjusted data set.
National Time Series | Climate at a Glance | National Centers for Environmental Information (NCEI)
An easy way to test time of observation bias is to split the stations into two groups – morning stations and afternoon stations. The trends are almost identical, but morning stations are warmer because people in warmer climates are more likely to go outside and take readings during the morning.
This the split of groups for Missouri. The afternoon stations were more than half a degree cooler.
1936 Morning Stations USC00232809.dly : FARMINGTON MO 37.7922 -90.4103 USC00234271.dly : JEFFERSON CITY WTP MO 38.5853 -92.1825 USC00234705.dly : LAMAR 7N MO 37.5983 -94.2842 USC00234825.dly : LEBANON 2W MO 37.685 -92.6939 USC00234850.dly : LEES SUMMIT REED WR MO 38.8803 -94.3358 USC00234904.dly : LEXINGTON 3E MO 39.1828 -93.855 USC00235541.dly : MEXICO MO 39.1756 -91.8861 USC00235671.dly : MOBERLY MO 39.4194 -92.4369 USC00235834.dly : MTN GROVE 2 N MO 37.1542 -92.2619 USC00238523.dly : UNIONVILLE MO 40.475 -93.0031 1936 Afternoon Stations USC00230204.dly : APPLETON CITY MO 38.1872 -94.0283 USC00230856.dly : BOWLING GREEN 1 E MO 39.3444 -91.1711 USC00231037.dly : BRUNSWICK MO 39.4247 -93.1331 USC00231364.dly : CARUTHERSVILLE MO 36.1875 -89.66 USC00231711.dly : CLINTON MO 38.395 -93.7711 USC00231822.dly : CONCEPTION MO 40.2394 -94.6833 USC00232289.dly : DONIPHAN MO 36.6206 -90.8125 USC00235027.dly : LOCKWOOD MO 37.3908 -93.9492 USC00235253.dly : MARBLE HILL MO 37.3036 -89.9664 USC00235976.dly : NEOSHO MO 36.865 -94.3603 USC00237263.dly : ROLLA MISSOURI S&T MO 37.9567 -91.7761 USC00237963.dly : SPICKARD 7 W MO 40.2472 -93.7158 USC00238051.dly : STEFFENVILLE MO 39.97 -91.8875 USC00238223.dly : SWEET SPRINGS MO 38.9664 -93.4194 USC00238466.dly : TRUMAN DAM & RSVR MO 38.2597 -93.4136 USC00238725.dly : WARRENTON 1 N MO 38.835 -91.1386
One adjustment has some legitimacy. There has been a large loss in stations over the past 30 years, which has caused the average latitude to move north.
Using only the set of stations with a 100 year long record, there is more warming over the past 30 years.
The number of hot days is not much affected however.