Historical Marine Air Temperature data are also available from the KNMI Climate Explorer website.
It’s most commonly referred to as Nighttime Marine Air Temperature (NMAT). The data presented in this post is the Met Office Historical Marine Air Temperature, version MOHMAT4.3. Refer to the Met Office Hadley Centre Observations Datasets webpage here:
Most presentations of the NMAT are for the Global and Hemispheric data sets. Figure 1 is Figure 3.4 from the IPCC AR4. Its representations of NMAT, what’s identified as HadMat, the green curves in cells A, C, and D, are significantly different from the data provided through the KNMI webpage, probably as result of the differences between the HadMat and the MOHMAT4.3 data sets.
This post illustrates the NMAT for ocean subsets, where possible, in addition to Global and Hemispheric datasets, all based on the MOHMAT4.3 data. The graphs are of the raw data and of the data smoothed with a 37-month running-average filter. All of the graphs end in May 2007, the last month of updates for the KNMI version of the MOHMAT4.3 data.
A minor problem: data is sparse in the late 1910s and the early 1940s for many of the datasets. For this reason, I’ve also included the graphs provided by KNMI in the lower right-hand corner of each illustration. They show the gaps in the data very well.
Figure 2 shows the Global NMAT from October 1904 to May 2007. The first thing that stands out is the peak in NMAT in the early 1940s, which was created by the sizable multiyear (1939/40/41/42) El Nino. (As noted in my post A Different Way to Look at NINO3.4 Data, that El Nino exceeds the intensity of the 1997/98 El Nino if the data is smoothed with a 25-month filter. Refer to Figure 2 in that post.) The second thing: using the smoothed curve as reference, current NMATs are only 0.06 Deg C higher than they were in the early 1940s.
The NMAT data from November 1905 to May 2007 for the Southern Hemisphere is shown in Figure 3. The gap in the data during the early-to-mid 1940s could not have come at a more inopportune time. It obliterated the impact of the multiyear El Nino. Note that there are no blank periods in the Southern Hemisphere NMAT data in the IPCC graphs for those periods. Refer back to Figure 1, cell d. There’s little to no data available, yet the IPCC shows it. Curious. Also note that, again using the smoothed data in Figure 3 as reference, there has been little, if any, rise in Southern Hemisphere NMAT since the mid-1980s.
Figure 4 illustrates the Northern Hemisphere NMAT data from January 1881 to May 2007. Prior to approximately 1905, there are significant breaks in the data, but since then, the data set is complete for the most part. There are a few months missing here and there, but no multiyear periods. Note how insignificant the difference is between the peak in the 1940s and the peak attributable to the 1997/98 El Nino. There’s approximately a 0.04 deg C difference.
OCEAN DATA SETS
The duration and number of breaks in the NMAT data for the South Atlantic, Figure 5, were so long and many it didn’t seem worthwhile to create my own graphs. I’m providing Figure 5, the corresponding graph from the KNMI website, simply as a reference.
The Indian Ocean NMAT data from February 1956 to May 2007 is shown in Figure 6. Highlighted is the dip and rebound from the late-19th Century to the mid-20th, which is consistent with many ERSST.v2 datasets. Also note how the NMAT for the Indian Ocean has not risen since the late 1980s.
Figure 7 shows the North Atlantic NMAT data from January 1867 to May 2007. The three spikes in the raw data stand out. The 1878 spike in NMAT coincides with a significant El Nino, similar the 1940s and the current stretch of elevated NMAT. The recent rise is also aided by Thermohaline Circulation/Meridional Overturning Circulation.
My favorite graph of the MOHMAT4.3 data is that of the Pacific Ocean NMAT from May 1921 to May 2007. Refer to Figure 8. Consider that the Pacific Ocean covers more of the global surface area than all land masses combined plus another Africa. And its NMAT in the early 1940s was higher than present values. It’s an indication of the magnitude of that multiyear El Nino. Somehow, that 1940s El Nino is not as significant in land surface temperature data.
There is little similarity between the NMAT data presented by the IPCC in AR4 and the Hadley Centre NMAT data available from through the KNMI website.