Some more relevant quotes from Foster & Rohling:
"The compiled CO2 and sea-level records cover about two thirds of the last 40 My, but not in a continuous fashion (Fig. 2), and we restrict our selection to the time periods with the highest density of data for both sea-level and CO2. Although other variables and boundary conditions that influence ice growth/retreat also may have changed between the time intervals (e.g., ocean gateway configurations, continental positions, and orography), we focus here on establishing the first-order relationships and accept that these may be refined further by future studies."
"There is a clearly sigmoidal relationship between sea level and climate forcing by CO2. Moreover, there is a striking similarity between data from different time periods and those generated by different techniques (e.g., Fig. 3A). This overall agreement implies that this relationship is robust and reflects the fundamental behavior of the Cenozoic climate system, despite some significant changes in boundary conditions (e.g., closing of the Panama Gateway since the Pliocene, closure of Tethys since the Miocene)."
"In the Pleistocene (CO2 < 280 ppm), there is no evidence of hysteresis beyond a few thousand years; intervals with increasing and decreasing CO2 give a similar sea-level response (Fig. 1), as also was elaborated for the relationship between sea level and temperature in that period (9). Similarly, for the Miocene (CO2 < 450 ppm), there is no evidence of hysteresis within a temporal resolution of ~300,000 y (Fig. 2). Conversely, the Eocene–Oligocene data show some suggestion of hysteresis (SI CO2 and Sea-Level Estimates and Fig. S3). As yet, this remains insufficiently defined, but it concerns only times with CO2 > 800 ppm (Fig. S3)."
"This assessment (Fig. 3B) clearly reveals a sea-level “plateau” at around 22 m between CO2 levels of about 400 and 650 ppm, with average 68% confidence limits for this interval of +13/−12 m, which covers sea-level values that might be expected in the absence of GrIS and WAIS [+14 m (31)], although within the bounds of uncertainty, we cannot rule out that there was an additional component of mass reduction in the EAIS at these midlevel CO2 values (18, 32). Based on the probability maximum and full contributions from GrIS and WAIS, this may have been equivalent to about 10 m of sea-level rise."
"Our observed long-term relationship between sea level and CO2 forcing reaffirms the importance of CO2 as a main driver of changes in the Earth’s climate over the past 40 My."
"We observe a lack of long-term sea-level response for CO2 levels between about 650 and 400 ppm. This suggests that during these times, very little continental ice grew (or retreated); presumably CO2 was too high, hence the climate too warm to grow more continental ice after the “carrying capacity” of the EAIS had been reached (Fig. 3A). It also suggests that 300–400 ppm is the approximate threshold CO2 value for retreat and growth, respectively, of WAIS and GrIS (and possibly a more mobile portion of EAIS). Sea levels of 20–30 m above the present during the Pliocene and Miocene, when CO2 was largely between 400 and 280 ppm, are thought to predominantly reflect mass changes in the GrIS and WAIS (26, 31). However, recent records proximal to the Antarctic ice sheet indicate that some portion [maybe as much as 10 m sea-level equivalent (26, 34)] of the EAIS also retreated during these warm periods (26, 35)."
"Although the overall shape of our ln(CO2/C0):SL relationship is similar to that inferred using inverse modeling of the benthic foraminiferal δ18O record (39), our compilation places the transition from a nonglaciated to fully glaciated EAIS at considerably higher CO2 (650–1,000 ppm CO2 vs. their 380–480 ppm CO2; Fig. 3C)."
"Because it is constrained by real-world observations of the Earth system, our relationship inherently includes all feedbacks and processes that contribute to sea-level change. It also appears to be largely independent of other boundary condition changes and therefore may be used with confidence to determine a likely estimate for sea level if theEarth system were to reach equilibrium with modern or future CO2 forcing. Given the present-day (AD 2011) atmospheric CO2 concentration of 392 ppm, we estimate that the long-term sea level will reach +24 +7/−15 m (at 68% confidence) relative to the present. This estimate is an order of magnitude larger than current projections for the end of this century [up to 2 m; best estimate, 0.8 m (41)] and seems closer to the worst-case long-term sea-level projection portrayed by Meehl et al. (1)."
