Baart, van Koningsveld, and M. Stive (2012) are commended for a stimulating discussion of sea-level trend analysis.
We were surprised by the reaction to Houston and Dean (2011) because we reached conclusions in agreement with several earlier studies and made no attempt to project sea-level rise into the 21st century. The issue is not whether data show a small acceleration (as found by Church and White, 2011) or deceleration (as we and others found) of sea level in the 20th century. In either case, the values are so close to zero that the trend is essentially linear. Woodworth et al (2009) note, “However, little evidence has been found in individual tide gauge records for an ongoing positive acceleration of the sort suggested for the 20th century itself by climate models.” This mirrors the conclusion in the seminal article by Douglas (1992) that said, “There is no evidence for an apparent acceleration in the past 100+ years that is significant either statistically, or in comparison to values associated with global warming.” Houston and Dean (2011) highlight the lack of understanding of 20th century sea-level rise and the challenge this offers to projecting into the 21st century.