With atmospheric CO2 at 0.040% by volume, globally averaged sea-level rise at the coasts is just under +1.5 mm/year.
When atmospheric CO2 was at 0.031% by volume, globally averaged sea-level rise at the coasts was just under +1.5 mm/year.
The difference is that climate alarmists think the current +1.5 mm/year is catastrophic and caused by human release of CO2, and the +1.5 mm/year 85 years ago was natural and inconsequential.
However, the similarity between the two numbers — the catastrophic 1.5 mm/yr and the inconsequential 1.5 mm/yr — has confused even some liberals into backing away from the One True Climate Faith. Even President Obama’s former Undersecretary for Science, Steven Koonin, has written that:
“Even though the human influence on climate was much smaller in the past, the models do not account for the fact that the rate of global sea-level rise 70 years ago was as large as what we observe today.”