You should check out this study as it highlights some of the uncertainties involved in estimating global mean temperature anomaly to within such fine limits.
Some highlights:
“We do not know even now how far from truth the readings recorded are on any stand, but only how far they differ from a certain standard, and that standard is believed to be somewhat faulty”
Before any further policy decisions are to be made on the grounds of a warming climate, full and complete analysis of the air and sea-surface temperature record must be engaged, completed, and reported by multiple independent professionally disinterested and metrologically expert third-party engineering groups. Only this will resolve the forefront problem of reliability brought into focus here. Notions of unprecedented warming and disastrous outcomes deriving from the previously published air-temperature record are scientifically unsustainable. Their wider significance must, instead, await unconflicted metrological and economic analyses. Causality remains deeply at issue [256,257,258,259,260,261].
Direct evidence of a warming climate since the 19th century includes the lengthened growing season, the revegetation of the far North, and the poleward migration of the northern tree line [274,275,276,277,278,279,280,281,282,283]. However, at the 95% level of uncertainty, neither the rate nor the magnitude of 19th or 20th century warming can be known. A more detailed appraisal of errors may modify the uncertainty bounds, but an alternative conclusion is unlikely.The 20th century surface air-temperature anomaly, 0.74 ± 1.94 °C (2σ), does not convey any knowledge of rate or magnitude of change in the thermal state of the troposphere. Climate alarm on that account is unjustifiable. The Joule-drift that certainly plagued all LiG thermometers manufactured prior to 1885 obviates the reliability of earlier air-temperature measurements. The global averaged surface air-temperature anomaly record cannot sustain any notion of unprecedented climate warming over the last 200 years, or over any other timespan.
