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—about one foot per century.
What are the facts?
In the period 1870-1924, the rate of sea-level rise was 0.8 mm/yr.
In 1925-1992, the rate was 1.9 mm/yr, and in 1993 -2014 the rate was 3.2 mm/y. So the rate has quadrupled in the last century, from 0.8 mm/yr to 3.2 mm/yr.
The rate data can be found here, from Sato and Hansen. (Data were last updated in May 2014).
Basic climate really is settled. While we don't know everything, we know enough. The rise of atmospheric carbon dioxide is causing problems now,and will cause bigger problems in the future.
Koonin doesn't think we know enough to set good climate policy.
He's wrong: policy should be on the supply side, phase out fossil fuels (petroleum, coal, natural gas) and substitute solar, wind, hydro and nuclear instead.
On the demand side, greater energy efficiency.
We don't know everything, but we know enough.
Sea-level rise was important in the $65B damages inflicted by Hurricane Sandy on the tri-state NY metro area (NY, NJ, CT) in 2012. Koonin is now at NYU, whose whose Langone Medical Center sustained $1.13B in damages, and the patients had to be evacuated.
Before NYU, Koonin was chief scientist at the oil company BP.