The IPCC explains measuring sea levels is not as simple as filling a bathtub because sea level rise is affected by many things including “ocean currents, winds, the Earth’s gravity field and land height.” As a result, they state it is a mistake to think any melting of ice anywhere will rise the ocean uniformly across the globe. (AR5 FAQ 13.1 Page 1149)

Based on tide gauge records the IPCC believes the global mean sea level (GMSL) has risen by 0.19 m between 1901–2010, noting it is “very likely” the sea level has risen 1.7mm each year from 1901 to 2010. Then increasing to 3.2mm between 1993 and 2010, or almost double. (AR5 Chapter 3 Executive Summary Page 258)

The IPCC expresses “medium confidence” that wave height has increased since the 1950s based on things like ship observations in North Atlantic Ocean north of 45°N. Up to 20cm per decade. (AR5 Chapter 3 Executive Summary Page 258)

The IPCC notes with “medium confidence average sea level rise has not exceeded ~ ±0.25 m on time scales of a few hundred years in the last 2000 years”. (AR5 Section 13.2.1.4 Page 1146)

These next comments focus on the time period of 3000 to 7000 years ago when the sea level is known to have risen the most since the ice age.  

The IPCC notes the sea has “likely” risen 2 to 3 meters in the last 3000 to 7000 years. (AR5 Section 13.2.1.4 Page 1146)

The IPCC goes on to note improvements in their understanding of the history of sea level rise since AR4, with a focus on the last 7000 years. (AR5 Section 13.2.1.4 Page 1146)

Personally, I find this is interesting because for the most part the IPCC ignores the temperature data from 3000 to 7000-year timeframe despite GISP showing the temperature on the century scale was much higher than today during that time period.

The IPCC does little to explain this past temperature change. Personally, I would even claim the IPCC goes out of their way to ignore temperature data from this time period as well as others. I discuss this more in my temperature chapter.