Mann et al are back at it; this time their alarmism is about sea levels rising.
Sea level has risen an average of 4 feet per century since the end of the Ice Age: 420 feet in 100 centuries. Fortunately, almost all of it occurred in a short period 10,000 years to 8,000 years ago. Since then sea level reached 10 to 20 feet higher than now during the 10 degrees warmer Holocene Optimum until reaching a peak about 3,000 years ago, then started falling. However, the Medieval Warm Period featured 12th Century sea levels eight inches higher than now, the Little Ice Age had sea levels 12 inches lower, and for the past four centuries sea levels have been increasing an average of six inches per century, and the rate of increase has been falling in the past half century.
It doesn't appear that alarmist studies reflect the sea level history going back 10,000 years when sea level was 420 feet lower, or the fluctuations in the six periods of warming in that period, of which the current period is the least. The only thing that makes the current warming seem remarkable is that it follows the Little Ice Age, which was the coldest period since the end of the Ice Age. We have actually been on a cooling trend since the end of the Holocene Optimum about 4,000 years ago; each succeeding warm period has been cooler than the preceding.
None of this is conjecture about atmospheric carbon dioxide; it was much lower than now even though average temperature was higher. None of this requires computer models; it's all been compiled in studies reported voluminously in books such as H H Lamb's "Climatic History and the Future" published in 1977. No trees had to be bored and cored, and analyzed for growth factors such as moisture, temperature, carbon dioxide fertilization, divergence from the instrumental record, and the like. Instead, such records as crops - vineyards in England 1,000 years ago - glacier retreat and advance, coral mounts that were 10 feet above current sea level 3,000 years ago, and sediments that indicated ocean temperature was 10 degrees Fahrenheit warmer then.
These current studies seem detached from other science and climatic history. They exist in a land of make believe, where what you desire now changes the past to fit the present.
Soviet historians did this whenever present facts made an event in the past an inconvenient truth. I thought that all ended around 1984, but "science" seems to have picked it up as the Soviet Union collapsed. Perhaps science will be next...