Are You New To the Global Warming Debate? James Hansen Admits a Couple of Things about Global Temperatures and Sea Levels You Should Know

Yale University’s Katherine Bagley interviewed James Hansen, former director of NASA’s Goddard Institute for Space Studies, in the post For James Hansen, the Science Demands Activism on Climate at YaleEnvironment360.  That interview was replayed in the article Climate scientist James Hansen ‘I don’t think I’m an alarmist’ at The Guardian.

In that interview, Hansen admitted a couple of basic things that many people do not realize.  So if you’re new to discussions of global warming and rising sea levels read on.

First, global surface temperatures were warmer during the last interglacial than they are today.  An interglacial is a period between ice ages.  That will be news to many readers.

How then, many will wonder, do we know for sure that the recent warming was caused by manmade greenhouse gases since we’re still within the realm of natural variability?

Of course the answer is: Climate models tell us so, even though those climate models are not simulating Earth’s climate as it existed in the past, as it exists now, and as it might exist in the future…climate models do not simulate naturally occurring ocean-atmosphere processes that can cause global warming.

Hansen’s second admission was sea levels were 6 to 9 meters (20 to 30 feet) higher during the last interglacial than they are today.  Here’s an illustration from my ebook On Global Warming and the Illusion of Control – Part 1 (700+ page, 25MB .pdf).  Hansen may have been a little conservative with his estimate.

Figure Intro-17

But what Hansen failed to say is that paleoclimatological studies have indicated that it took a number of millennia for sea levels to rise those 6 to 9 meters when temperatures were warmer than today. See:

The corresponding portion of the Hansen interview (my boldface and brackets):

James Hansen: We know from the earth’s history that 2 degrees would eventually lead to sea level rise of several meters. The last inner glacial [sic] period,  [that should read interglacial period] 120,000 years ago, that’s the last time it was warmer than today, sea level was 6 to 9 meters higher — that would mean loss of almost all coastal cities. It’s unthinkable that we walk into such a situation with our eyes open, and yet, the science is very well understood.

There’s no argument about the fact that we will lose the coastal areas, now occupied by most of the large cities of the world. It’s only a question of how soon. That message, I don’t think, has been clearly brought to the policymakers and the public…

If I was new to the discussions of global warming and sea level rise, that would be as far as I would have needed to read the interview.  He would have turned me into a skeptic right there.

But contrary to his claims about alarmism, Hansen then goes on to play alarmist and discuss how his recent modeling efforts and resulting paper indicate that the rise maybe-sorta-could occur abruptly.

… More than 190 nations agreed [at the Paris climate conference last December] that we should avoid dangerous human-made climate change. That loss of coastal cities would be a dangerous outcome. It’s hard to imagine that the world will be governable if this happened relatively rapidly. What we conclude is that the timescale for ice-sheet disintegration is probably a lot shorter than has been assumed in the intergovernmental discussions.

Of course, even proponents of the hypothesis of human-induced global warming found the recent Hansen et al. (2016) study (Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous) to be nonsense. Even the title of the paper includes the oft-used weasel words “could be”.  See the following posts at WattsUpWithThat:

CLOSING

Two quotes from my ebook On Global Warming and the Illusion of Control – Part 1.

From the Closing to Chapter 1.16 – Sea Levels Are Rising:

This chapter opened: For many people, especially for persons living near the coasts, sea level is the critical metric associated with global warming and climate change.

Sea levels have risen since the peak of the last ice age, and, if history repeats itself, they will continue to rise to the heights achieved during the last interglacial: 5 to 10 meters (16 to 32 feet) higher.

But as discussed in this chapter, there are a multitude of factors that can contribute to the rise, or fall, in local sea level. Rising sea levels are, therefore, a local concern, as are steps to combat it, as I’ve noted numerous times in this chapter. Many countries and communities are already implementing measures to reduce the impacts of rising sea levels—employing methods designed specifically for their location.

Assuming that man-made greenhouse gases have contributed to the rate at which global sea levels are rising, curtailing man-made greenhouse gas emissions would only slow the rate, not stop it. Then again, The Houston & Dean (2010) Sea-Level Acceleration Based on U.S. Tide Gauges and Extensions of Previous Global-Gauge Analyses found that the rise in sea levels had not accelerated with global warming.

And from the Introduction, I began the discussion under the heading of SEA LEVELS, ON THE OTHER HAND, PRESENT AN ENTIRELY DIFFERENT PROBLEM:

Again, even if we could turn back CO2 levels to preindustrial values, sea levels would continue to rise. Sea levels have been rising since the end of the last ice age, and they will continue to do so until Earth cools once again and we head toward another ice age. That is, the only way to stop sea levels from rising is to start accumulating water on land in the form of ice.

Further, the rate at which global sea levels might possibly change in the future, in response to the hypothetical effects of man-made greenhouse gases, is still the subject of wide ranges of uncertainty and open debate…and the subject of even more alarmism from activists and the media, if that’s possible.

And I closed the discussion under that heading with:

The ridiculous suggestions by politicians and alarmists that we can control rising sea levels by reducing greenhouse gas emissions is one of the primary reasons for the title of this book: On Global Warming and the Illusion of Control.

UPDATE:  I corrected a typo in the opening sentence.

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About Bob Tisdale

Research interest: the long-term aftereffects of El Niño and La Nina events on global sea surface temperature and ocean heat content. Author of the ebook Who Turned on the Heat? and regular contributor at WattsUpWithThat.
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7 Responses to Are You New To the Global Warming Debate? James Hansen Admits a Couple of Things about Global Temperatures and Sea Levels You Should Know

  1. Frank says:

    Bob wrote: “Again, even if we could turn back CO2 levels to preindustrial values, sea levels would continue to rise. Sea levels have been rising since the end of the last ice age, and they will continue to do so until Earth cools once again and we head toward another ice age. That is, the only way to stop sea levels from rising is to start accumulating water on land in the form of ice.”

    If you look carefully, SLR slowed during the Holocene and effectively came to a stop about 2000 years ago. The rate of SLR for a century before 1970 (when surface warming attributed by the IPCC to man became significant), SLR was about 13 cm (or 0.13 m or 5 inches). (I’m not paying any attention to the trend lines, just the overall rise.)

    If SLR preceding the 1870-1970 century equaled the rate during the last two millennium, it would be 1.3 m/millennium and total 2.6 m over the last 2 millennia and 5.2 m over the last 4 millennia. That would be easy to detect in the Holocene record of SLR:

    On this graph, SLR appears to be about 0 m/millennia for the last two millennia and about 1 m over the previous 2 millennia. So the difference between 0 and 0.5 m/millennia (5 cm/century) is detectable, but a rate half as big may not be. Therefore, even the 1870-1920 warming rate of 0.8 m/millennium (0.8 mm/yr) would be apparent if it had persisted (on the average) for the previous two millennia. The last time SLR was about 1 m/millenium was 4-7 millennia ago.

    My interpretation (FWiW) is that slow cooling after the Holocene Climate Optimum finally brought SLR to a halt (less than 0.2 m/millennium) about 2000 years ago and a near halt 4000 years ago. SL probably rose and fell slightly during warm and cold period such as the MWP and the LIA. The early tide gauge record detected the slight rise (0.1 m) associated with the end of the LIA. The rapid two decades of warming ending around 1940 (unforced variability) boosted SLR and sometime after 1950, AGW probably began replacing the LIA as the main cause of SLR.

    There is a lot of guess work in this interpretation. However, there is no possibility that the previous 2 millennia experienced a rate of SLR comparable to the 20th century. It is possible those millennia experienced an average rate of SLR that was 20% of the rate during the 20th century.

  2. Bob Tisdale says:

    Sorry, Frank. I can’t confirm or counter your interpretation of the paleo graph for the last 2000 years. The thickness of the black line is roughly one meter.

    Also, your first graph gives the impression that the trends for the satellite era are highest since 1870. First, the Church and White data are based on tidal gauges along shorelines while the satellites are measuring sea level for the global oceans that have received numerous adjustments. Second, the trends are for greatly different time periods. But if we look at the 21-year running trends of the tidal gauge data (blue curve), we can see that the trend of the 21-year period ending in the early-1960s far exceeded the satellite-based trend (red horizontal line).

    That graph is from Chapter 1.16 of “On Global Warming and the Illusion of Control – Part 1
    https://bobtisdale.files.wordpress.com/2015/11/tisdale-on-global-warming-and-the-illusion-of-control-part-1.pdf

  3. Frank says:

    Thanks for the reply, Bob. I agree with both of your comments, but not your conclusion. Print the graph of SLR for the last 9 millennia at Wikipedia (my link failed) and draw lines of various slopes on that graph:


    2 m/millennium (mm/y) – overall 20th century SLR from tide gauges
    1 m/millennium (mm/y) – roughly “post LIA, pre-GHG-mediated-warming” SLR (tide gauge)
    0.5 m/millennium (mm/y) – detectably different from zero over several millennia?
    0.25 m/millennium (mm/yr) – detectably different from zero over several millennia?

    I believe you will find the slope of the line from 4000-7000 years ago is roughly 1 m/millennium, which is clearly distinguishable from the slope from 4000 to present and especially 2000 to present. Could what has been happening over the last century have been happening for the last several millennia? Decide what you believe for yourself.

    You can see the scatter in the data that created the central estimate. There is substantial disagreement between sites, but a clear overall trend towards reduced SLR over the last 7 millennia. This is what one would expect for a Holocene with a stable or (more accurately) slightly falling temperature. No one could have predicted ahead of time when SLR would reach a plateau, but it clearly did over the last two millennia (IMO). By plateau. I mean SLR less than observed by the tide gauge record OVER A CENTURY. I’m not interested in decadal fluctuations or whether acceleration has been detected or the difference between various compilations of tide gauge records. Just the big picture: Could what has been happening over the last century have been happening for the last several millennia?

    If the rising SLR seen a the beginning of tide gauge record were caused by the end of the LIA, then one would expect to see wiggles in SL due to the LIA, MWP, RWP, CWP and similar century+ long warming and cooling periods. However those wiggles would be undetectable the Holocene SL graph because they didn’t persist for long enough to escape the noise.

    It is surprising that there has been little effort to fill in the gap between tide gauge SLR and millennial SLR. The paper below tries, but I don’t trust a method validated only during a period of rising SLR.

    http://www.pnas.org/content/108/27/11017.full

  4. Bob Tisdale says:

    Thanks for the link, ren. I was saddened to hear of Bill Gray’s death.

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