It seems the uptick in the 20th century is not real, being nothing more than an artifact of shoddy procedures where the dates on the proxy samples were changed for some strange reason.
The final date of the Marcott reconstruction is AD1940 (BP10). Only three cores contributed to the final value of the reconstruction with published dates (“pubend” less than 10): the MD01-2421 splice, OCE326-GGC30 and M35004-4. Two of these cores have very negative values. Marcott et al re-dated both of these cores so that neither contributed to the closing period: the MD01-2421 splice to a fraction of a year prior to 1940, barely missing eligibility; OCE326-GGC30 is re-dated 191 years earlier – into the 18th century.
Re-populating the closing date are 5 cores with published coretops earlier than AD10, in some cases much earlier. The coretop of MD95-2043, for example, was published as 10th century, but was re-dated by Marcott over 1000 years later to “0 BP”. MD95-2011 and MD-2015 were redated by 510 and 690 years respectively. All five re-dated cores contributing to the AD1940 reconstruction had positive values."
Flat-out fraud–which, sadly, has come to typify the climate alarmism movement." As stated, it's a vast conspiracy out to dupe the ignorant. How many carbon credits are in your wallet?
In short, the global warming movement is corrupt to the core.