Six years ago, it anticipated ocean levels would be 48.5 centimeters higher than they are currently. In this year’s report, the estimated rise is 38.5 centimeters on average.
But the 38.5 number Lomborg presents does not include increases from accelerating ice flows. About these, the report says:
For example, if this contribution were to grow linearly with global average temperature change, the upper ranges of sea level rise for SRES scenarios shown in Table SPM-2 would increase by 0.1 m to 0.2 m. Larger values cannot be excluded, but understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea level rise.
IPCC lead author Kevin Trenberth (speaking on Science Friday) spoke on the sea level projections:
“The numbers in this report are actually very similar to the previous report, however they are reported in a somewhat different way”
This is especially interesting since it fundamentally rejects one of the most harrowing scenes from Al Gore’s movie An Inconvenient Truth. In graphic detail, Mr Gore demonstrated how a 20-foot [6 metres] rise in the sea level would inundate much of Florida, Shanghai, and the Netherlands. The IPCC report makes it clear that exaggerations of this magnitude have no basis in science – though clearly they frightened people and perhaps will win Mr Gore an Oscar.
Actually the report says:
The corresponding future temperatures in Greenland are comparable to those inferred for the last interglacial period 125,000 years ago, when paleoclimatic information suggests reductions of polar land ice extent and 4 to 6 m of sea level rise.
Now you could fault Gore for not saying how long this would take, but it doesn’t look like there is a good estimate for this.
The report also revealed the improbability of another Gore scenario: that global warming could make the Gulf Stream shut down, turning Europe into a new Siberia. The IPCC simply and tersely tells us that this scenario – also vividly depicted in the Hollywood movie The Day After Tomorrow – is considered “very unlikely”.
Which means that they think that there is a 5-10% chance of it happening. It’s not that improbable that Gore would have been justified in ignoring it.