Sea level rise study misrepresented; humans still raising sea level

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There is a new paper out in the Journal of Climate which some have hailed as proof that the global mean sea level is not influenced by human activity. However, this is exactly the opposite of what the study authors explain are the real results.

The following guest post is a briefing note by the Climate Science Rapid Response Team:

There is a new paper out in the Journal of Climate which some have hailed as proof that the global mean sea level is not influenced by human activity. However, this is exactly the opposite of what the study authors explain are the real results.

The study finds sea level rise is still continuing at a steady rate.  Study author Dr. John Church has stated via email correspondence, “I would argue that there is an unhealthy focus on one single statistic -- an acceleration number -- and insufficient focus on the temporal history of sea level change.”

Dr. Church further explained that the reason for a relatively steady rate of rise is partially due to the large rate of CO2-induced warming throughout the century.  Melting glaciers contributed extensively to sea level rise in the first half of the century, but in more recent years there is less ice left to melt. This contributes to a steady rather than accelerating sea level rise.

The study also found that thermal expansion of the seas should be reflected more strongly in climate models.

Over all, Dr. Church stated that the results “increase our confidence in models of sea level change and thus increase our confidence in the projections for the 21st century.”

With a complete reading of the paper, it becomes apparent that acceleration is only one part of the larger picture. The planet is rapidly warming and the seas are rising. These researchers are refining our understanding of which factors are driving that rise, and in what proportions.

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4 Responses to Sea level rise study misrepresented; humans still raising sea level

  1. Adam Welz says:

    It seems to me that the last sentence of the abstract,

    "Semi-empirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of our closure of the budget is that such a relationship is weak or absent during the 20th century."

    is the source of the confusion, as it says that climate change has nothing to do with sea level rise. Is this what the authors meant to say?

    • John Abraham says:

      Early in the century there were more significant ocean level rises from melting glaciers, and as glaciers melt away there is less to melt. Consequently, the early glacier melt is decreasing. This fact makes the acceleration smaller.

      So what does this have to do with global temperatures? Let’s say that temperatures rise in the higher northern latitudes but overall, global temperatures are constant. You might see a sea level rise occur (even with no increase in global temperatures) because the increase in temperatures occur where there is ice to melt. As a for instance, in the early part of the century there was a warm spell in Greenland, which would cause melting of ice sheets. Greenland can begin to melt even though global temperatures are constant. In fact, we expect temperatures to rise more in some areas than others. Or, we expect temperature to rise in some areas before it rises in others.

      In short, saying that the relationship between global climate change and sea level rise is weak is not the same as saying “climate change has nothing to do with sea level rise."

      Make sense?

      Dr. John Abraham
      University of St. Thomas
      School of Engineering
      St. Paul, MN 55105-1079

    • Jason Box says:

      In addition...Two factors dampen the accelerating mass loss from the Greenland ice sheet in the 1840-2010 period. One is a 20% increase in ice sheet snow accumulation rate (Box et al. 2012) and the other is a 50% increase in meltwater retention in the snow (Box, 2012, in review). The latter has increased because of increasing melt and increasing snow accumulation.

      Box, J..E., Greenland ice sheet mass balance reconstruction. Part II: Surface mass balance (1840-2010), J. Climate, submitted 30 July, 2012. http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00373.1

      It's noteworthy also that my accumulation paper presents how Northern Hemispheric warming seems the cause for Greenland taking on more snow.

      Dr. Jason E. Box
      Byrd Polar Research Center and Dept of Geography
      The Ohio State University
      Columbus, Ohio

    • John Church says:

      I basically agree with what John Abraham has written.

      Sea level is more complex then just a simple linear relationship to surface temperatures. The physics is more complex than this and there are multiple time scales for each of the components contributing to sea level change. Glaciers are a good example. As temperatures continue to rise their contribution cannot continue to rise indefinitely because over time there will be a smaller glacier volume to contribute to sea level rise.

      John Church
      Center for Australian Weather and Climate Research
      CSIRO Marine and Atmospheric Research
      Hobart, Australia

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