Guest Post by Willis Eschenbach

My examination of objects cryospherical continues. In my last post, The Size of Icy Reflections, I showed that a change of 10% in the global sea ice area translates into a global average of a 0.1 watt per square metre (W/m2) change in reflected sunlight. In this post, I’ll look at what that means given the historical changes in ice area. This will highlight the kind of the curious choices made in the analysis of climate data. To start with, here is the full data from the Hadley Ice and Sea Surface Temperature dataset (HadISST, data link below).

Figure 1. Global total ice area, computed as the sum of 1°x1° gridcell area times the percentage of each gridcell covered by ice. Areas in millions of square kilometres (Mkm^2)

I’m sure you can see the “curious choice” I mentioned before. Clearly, the recent part of the data appears valid … and clearly the early part of the data is not. Obviously, before 1900 it’s just climatological (average) data of some kind. And examining the lower edge of the data that shows the minimum extent, it is also clear that nothing before around 1970 can be trusted … so where can we start analyzing the data?

An examination of the paper explaining the dataset reveals that we have reasonable data for the Arctic sea ice since the early 20th century, but for the Antarctic the paper says the following:

Before the advent of satellite-based imagery in 1973, sea ice concentration data for the Antarctic are not available, and sea ice extent data are not readily available for individual months, seasons or years, although some visible and infrared data do exist for 1966 – 1972 [Zwally et al., 1983] and some undigitized charts reside in national archives (e.g., V. Smolyanitsky, personal communication, 2002). Readily available information was limited to two historical climatologies of sea ice extent. Therefore our sea ice concentration analysis before 1973 is derived indirectly, and does not include any interannual variability, though there are some trends resulting from the differences between climatologies for different periods.

This gives me 1974 as a reasonable starting date for what data is good enough to analyze, as that would be the first year with complete data for both poles. Figure 2 shows that valid part of the ice area data:

Figure 2. As in Figure 1, starting January 1974 and ending January 2016. Areas in millions of square kilometres (Mkm^2)

To understand the variations in the ice area it is useful to “decompose” the signal by removing the repeating seasonal component of the data. Figure 3 shows the decomposition of the same data shown in Figure 2.

Figure 3. Seasonal decomposition, HadISST global sea ice data, January 1974 – December 2015. Upper panel shows the raw data. Middle panel shows the annually repeating seasonal component of the data. Bottom panel shows the raw data minus the seasonal component. Areas in millions of square kilometres (Mkm^2)

A contemplation of this figure reveals some interesting aspects. First, there is no significant trend at all in the 40+ years of satellite data. In other words, it seems the Awful Terrible Horrible Global Sea Ice Crisis has been cancelled due to lack of evidence.

Next, remember from above that a change of 10% in the global sea ice area translates into a global average of 0.1 watt per square metre (W/m2) change in reflected sunlight. From inspection of Figure 3, the sea ice area varied by ± 1 Mkm^2 around an average of just over 20 Mkm^2. This is a change of ± 5%, and thus should be accompanied by a change of ± 0.05 W/m2 in reflected sunlight … in other words, far too small to be measured.

However, this is not the only interesting finding. We’re pretty sure that the global average surface temperature increased from the mid-1970s to about 1998 (Figure 4 below). However, we see no sign of this in the global sea ice area data (Figure 3 above). Instead, ice area remained stable throughout the 1980s and the 1990s, while temperatures climbed.

Figure 4. Global surface temperatures per the HadCRUT4 temperature dataset.

Next, we’re also pretty sure that there was no significant change in the global average temperature from about 1998 to 2015, the end of the ice data. Despite that, starting in 2000 the ice area first dipped to a low in about 2007, and since then has been climbing rapidly.

This supports a curious conclusion, which is that in modern times at least, the global sea ice area is not particularly a function of the global average surface temperature. Go figure …

Gotta love settled science.

My best regards to everyone,

w.

My Usual Request: Misunderstandings are the curse of the internet. If you disagree with me or anyone, please quote the exact words you disagree with, so we can all understand the exact nature of your objections. I can defend my own words. I cannot defend someone else’s interpretation of some unidentified words of mine.

My Other Request: If you believe that e.g. I’m using a method wrong or using the wrong dataset, please educate me and others by demonstrating the proper use of the method or the right dataset. Simply claiming I’m wrong about methods doesn’t advance the discussion unless you can point us to the right way to do it.

Data: The Hadley HadISST ice (and sea surface temperature) data is available here. I used the NetCDF file HadISST_ice.nc.gz (~15Mb) at the bottom of the page.

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