To the editor: The treatment of sea level rise in “How scientists got climate change so wrong” (by Eugene Linden, Nov. 8) doesn’t accurately represent the reports from the Intergovernmental Panel on Climate Change. Regarding the future of the Greenland and Antarctic ice sheets over the 21st century, Mr Linden claims that the first IPCC report, in 1990, said that “the Antarctic ice sheets were stable,” when it fact it actually said that “the West Antarctic Ice Sheet is of special concern” and that both ice sheets “make a major contribution to the uncertainty in predictions.” He claims that the second IPCC report, in 1995, said that “little change was expected” in those ice sheets, when in fact it actually said that little change was expected “in the extent” of those ice sheets, an important distinction because “extent” refers not to ice mass but to surface area (currently estimated at a combined 6 million square miles). He claims that the third IPCC report, in 2001, projected a worst case of 70cm of sea level rise by 2100, when in fact Figure 11.2 of that report shows the potential for 88cm, plus more because of “uncertainty relating to ice-dynamical changes in the West Antarctic ice sheet.” And he claims that the fifth IPCC report, in 2013, had a “worst case” of 98cm of sea level rise, when in fact that report says that Antarctic ice sheet collapse could add “several tenths of a meter” and perhaps more.
A more accurate approach would emphasize the different probabilities in these estimates, which are not necessarily in conflict with each other. The 2017 NOAA “worst case” of 250cm cited by Mr Linden seems to represent the absolute maximum amount that is thought to be physically possible. Allow for a small amount of uncertainty and you may get a 2019 NOAA overview, which says that “scientists are very confident” that 200cm is the maximum possible sea level rise. Allow for even more uncertainty and you may get the 98cm in the fifth IPCC report: that’s the upper end of the “likely” range, meaning that the authors estimated a 17% chance that sea level would be higher than that level.