15
Nov
13

Global warming “hiatus” – it might be the ice

There has been a big guessing why the heck the plot of global atmospheric temperatures did not go straight up the last 18 or so years. hiatus 1964-2012

I plotted the curve from 1964 – 2012 here, with a linear fit for the data from 1964 to 1998, the beginning of the so called “hiatus”. (Data are frome here, with the NASA GISS temperature set as basis.)

As you can see,  there is not much of a hiatus. But if you look sharply, you could see after 1999, the red data points, a slow-down of atmospheric (not global!) warming, resulting in a lag of about 0.1 K.

The big hiatus rumoring through the press can be seen only, when we fit our straight line to a shorter period between 1985 and 1998, which is statistically questionable.

hiatus 1964-2012 fit1985-1998

Doing that means assuming, that atmospheric (not global!) warming did accelerate in the middle period. Now, we get a temperature lag of about 0.2 K against the expectation.

A lot of interesting work has been done to find an explanation for this fact, the most notable I know of by Foster and Rahmstorf, who calculated the deviations from the middle line caused by volcanoe eruptions and El-Nino/La-Nina events, the big southern pacific air and sea current oscillation, with linear contributions. They found out, that the “hiatus” can be explained quite well by these. Even more convincing was the simulation of Kosaka and Xie, who allowed for nonlinear feedback of El-Nino/La-Nina events to atmospheric temperature and got a theory – measurement accordance almost too good to be true. The British Met Office argued in a meticulous discussion, that a lot of the heat unaccounted for must be gone into the deep sea, which is no contradiction to the former.

arctic sea ice volumeBut there is one striking point, where a lot of energy has been dumped during the last 18 or so years: the arctic ocean. Let’s look at another plot: the volume of the ice floating on it (from here):

Between 1995 and today more or less 8000 km³ of perennial ice melted away. Could not the heat necessary to do this be reflected in the warming lag of the atmosphere? And it could.

Here is the copy of an excel sheet, the electronic equivalent of a back-of-envelope-calculation, in which I tried to find out, whether or not the ice loss could be correlated with the warming lag.



melting enthalpy of water 333 1,00E+03 J/kg
lost perennial ice volume since ca. 1995 8000 1,00E+09
density of ice 0,9 1,00E+03 kg/m³
lost perennial ice mass since ca. 1995 7200 1,00E+12 kg
heat used to melt lost ice mass 2397600 1,00E+15 J
2,3976 1,00E+21 J
mass of earth atmosphere 5,15 1,00E+18 kg
specific heat of air under standard conditions 1,05 1,00E+03 J/kgK
total heat capacity of the atmosphere 5,4075 1E+21 J/K
temperature decrease of the earth atmosphere (even distribution of heat contribution assumed) -0,44338419 1,00E+00 K
Difference between expected and real atmospheric temperature, ca. 0,1 1 K
antarctic volume gain rate 35,5 1,00E+09 m³/year
years since 1995 18
approximate gain since 1995 639 1,00E+09

The result is, that when the heat energy for the melting of the perennial arctic sea ice had been taken evenly from the hole of the atmosphere and from nothin else, and its specific heat capacity can be considered everywhere the same, a temperature lag of more than 0,4 K would have happened.

As is not so well known, the antarctic sea ice increased over the last decades, thus puzzeling once more the scientific community. Massonet and colleagues calculed this mass increase here. In the lower part of the spreadsheet, I looked at the size of this effect. It is not bigger than 10 % of the arctic loss.

This is all terribly incomplete of course. The atmosphere does not contribute evenly to the melting. A lot of the heat during summer melting comes not via the atmosphere, but directly from the solar radiation because of increasing surface absorption. It is quite possible, that a small shift in the regional radiation balance is responsible for the lions share of  the melting, as the sea ice simulation team of the University of Washington warns here. The atmosphere is pretty strongly coupled to the top layers of the continents and the seas, so those should have contributed to the melting, too.

On the other hand, the observed temperature lag is only 0.25 to 0.5 of what would be expected in an atmosphere-only model. So this seems to be somehow already accounted for.

It might not be the whole truth, but it’s worth looking at it.

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2 Responses to “Global warming “hiatus” – it might be the ice”


  1. 1 johnm33
    November 15, 2013 at 11:34 pm

    When I started thinking about GW I realised that the whole point of weather was to equalise local energetic imbalances, and what drove that was the difference in energy between the equator and the poles. The results of looking at any local weather would be as random or chaotic as the weather itself,[and you'd have to look everywhere to see the big picture] no the only place to look was the poles, since this is where the energy ends up. So if the poles are warming we have global warming if not, not. Piomas ice volume is the simplest proxy for that, it’s the coolant in ‘our’ aircon.
    As regards the antarctic it seems to me that the spread is caused by bottom melt of shelf and grounded ice which then flows to the periphery across the inverted landscape. Assuming a 1m average height of ice above sea level gives an average depth of 9m below sea level to the underside. Now offhand I can’t remember if its 6ft or 10ft which equals atmospheric pressure, and I don’t know the freezing temperature of water at those pressures, but my guess is that you have practically fresh water emerging at the edge of the ice sheet at below 0c easily frozen by southern winter temps, so I suspect the extra spread, or at least it’s volume, is a proxy for the hidden melt, not exact but a good indication and probably low.

  2. 2 Rob Dekker
    December 6, 2013 at 1:04 am

    Hi Dominik,
    Thank you for your creative calculations on the possible effect of Arctic sea ice volume loss on atmospheric temperature.

    I have a couple of comments on your analysis, basically to put your numbers into perspective.

    First, let us look at the “ocean heat content” over the past couple of decades, and how that changed over the decades :
    http://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/heat_content700m2000myr.png
    Notice that ocean heat content since 1995 changed by something like 1 * 10^23 J for the upper 2000 meter of oceans.

    That means that heat going into the oceans since 1995 is a factor 40 or so larger than the number you calculated for sea ice volume loss. Long term sea ice volume loss is thus almost negligible in the big picture of planetary heat balance.

    Alternatively, since sea ice melt is a “heat flux” from atmosphere into the oceans, you can calculate the effect of sea ice loss in terms of “flux” of “forcing” (in W/m^2). That makes it easy to compare this effect to other forcings (such as AGW).

    Let’s try that : To get the “heat flux”, start with your energy number : 2.4 * 10^21.
    Divide that energy number by 3600*24*365*18 seconds, to get to power (in Watt) needed to melt that ice over 18 years.
    Divide that power number by surface of the planet (5 * 10^14 m^2) and you obtain 0.0084 W/m^2.
    That is the “forcing” needed to melt that ice over 18 years.
    Hansen 2008 rounded that to 0.01 W/m^2 if I’m not mistaken.

    This makes the direct influence of sea ice volume loss on our planet’s temperature comparable to linear contrails (caused by aircraft) and a factor 10 smaller than even GHG effect of NOx changes over the same period.

    Interesting is also to compare this forcing to CO2 forcing changes over the same period.
    We are currently at 390 ppm, and adding some 2 ppm /year in CO2 to our atmosphere.
    A doubling of CO2 will create 3.7 W/m^2 forcing, so per year, we add 3.7 * 2/390 = 0.019 W/m^2 forcing.
    Over the past 18 years, we thus added some 0.34 W/m^2, a factor 40 more than sea ice loss over the same period.

    Finally, for comparison, loss of ice causes the Arctic to be darker and thus absorb more heat from the sun (this is the famous albedo feedback). There have been various analysis done to express that effect in a forcing, and they all end up in the 0.13-0.15 W/m^2 range (since 1980). Here is one easily explained, by Tamino :
    http://tamino.wordpress.com/2012/10/01/sea-ice-insolation/
    So the increase in heat due to melted sea ice over the long run appears to be a factor 10 or so larger than the heat it takes to melt the ice in the first place. That’s some scary feedback, no ?

    Any way, that was a very long comment to explain that the energy that was needed to melt sea ice over the past 18 years is not significant in the global energy balance, and thus CANNOT be responsible for any significant planetary temperature change over that period.


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