By Joseph D’Aleo, CCM, AMS Fellow
All the data sources have updated now for June. NOAA GHCN data was a clear outlier. NOAA called this the eighth warmest June on record for the globe in the 129 years since records began in 1880 with a positive anomaly of 0.5C (0.9F) for the month. The University of Alabama, Huntsville MSU satellite based global assessment reported that this June was the the 9th coldest in the 30 years of satellite record keeping (base period 1979-1998) with a value of -0.11C (-0.19F). The other NASA satellite source, RSS had June as the 13th coldest out of the last 30 years. Hadley came in today with their CRUV3 data update. They also were in disagreement with the satellite data sets with +0.316C, the 10th warmest June. However both the Hadley and MSU do show a downtrend since 2002 of 0.15 to 0.2C with a rather strong negative correlation (r = - 0.44 with Hadley) with CO2 which increased 3.5% over the period.
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Recall the CO2 was negatively correlated for almost 4 decades from the 1940s through the 1970s. It was positively correlated from 1900 to 1930s and again 1979 to 1998. This on-again, off-again relationship suggests CO2 is not driving the climate bus but maybe a passenger in the back.
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OK, but why the discrepancy of satellite and surface based data bases? Though there has clearly been some cyclical warming in recent decades, the global surface station based data is seriously compromised by urbanization and other local factors (land-use /land-cover, improper siting, station dropout, instrument changes unaccounted for and missing data) and thus the data bases overestimate the warming. Numerous peer-reviewed papers (referenced at end) in the last several years have shown this overestimation may be the order of 30 to 50%. I believe the recent warming is comparable or less than the warming in the 1930s and is now over. See a detailed analysis of this issue here.
Even the global continental extremes show no recent decade represented. All the heat records were before 1950 with the exception of Antarctica which showed its warmest temperature in 1974. There probably was very little monitoring in prior years there.