Immediately beneath this sentence is the interface of the ESRL Website at: http://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl
The interrogation that is entered in the form relates to sea surface temperature at 20-40° south latitude around the entire globe (0-360° longitude) taking into account every month of the year adjusting for the reducing circumference of the Earth as latitude increases, presented as a plot. That plot is below.
I live at 34° south latitude and at this latitude there is mostly ocean rather than land. Home is on the south-west coast of Australia where the winds are mostly onshore. So, air temperature tends to follow sea surface temperature. I am a farmer and all farmers take a strong interest in climate. I grow grape vines and make wine. The wine expresses the variations in the climate from year to year. To make good wine, the best wine possible, I need to know what is going on. I am told that the climate is getting hotter and I may need to plant later ripening varieties to avoid damaging heat during the ripening period.
All that we can say about this data is that temperature has increased in both winter and summer. But spring and autumn is important to me. The vine leafs out in spring and the fruit matures in autumn. I need to dig deeper.
The data can be acquired in the form of an array of monthly averages as seen below. Its a long sheet of data and I show you just the top and the bottom of the sheet.
I want to show you how to work with the raw data to get a much better idea of what is going on in your habitat. Since climate varies primarily according to latitude I define my own habitat, in the first instance, as a band of latitude. If you prefer, you can focus on just part of a latitude band and perhaps air temperature rather than sea surface temperature if you happen to live far from the sea. In this exercise I am going to focus on the entire band of latitude because I am interested in the way climate changes globally.
Copy the data directly from the ERSL website and paste using a simple ‘notepad’ format. Save this as a text file. This is what the notepad sheet looks like.
Next step is to import that data into a spreadsheet via the import wizard available in excel.
Below, the spreadsheet is represented in part with some calculations in red text and a graph of the data in red.
I have added each months data from January through to December and divided by 12 to yield the annual average. Then I have plotted the column in red. What can we see:
- There has been an increase of 0.4°C in temperature in this latitude band over the last 67 years. However, this is within the range of the most extreme inter-annual variability (more than 0.5°C) so it is possible that the factor causing the temperature to swing between the years is also responsible for the whole of period change.
- Extreme inter-annual variability prior to 1978 and much less after 1978.
The expansion of the Hadley cell and the consequent southward migration of the mid latitude high pressure cells after 1978 is a feature than many observers have remarked upon. High pressure cells dominate this band of latitude. Summers are dry. In winter fronts attached to low pressure cells that impinge at this time of the year bring rain. The lack of variability post 1978 suggests a reduced incidence of cold winds from the south. High pressure cells are relatively cloud free. If there is less cloud it can’t come and go. With an expansion of the Hadley cell one would see fewer fronts associated with low pressure cells so the fluctuations in surface temperature would tend to diminish along with the rainfall. Indeed rainfall has declined by 15-25% depending on location.
By adding all Januaries and dividing by 68 (68 Januaries) the average temperature for the month of January over the period 1948-2014 is obtained. It is 22.32°C. Paste the formula across the page. Graph the result as the average monthly temperature.
Average daily temperature is sub optimal for photosynthesis (25°C is optimal) in all months but daytime temperature in the height of summer is almost warm enough to be optimal. Growth of plants is very slow in the winter months. An extension of the warmth of February into the months of March through to June would increase plant productivity but unfortunately, without irrigation this can not happen. However, grape vines are hardy plants and this is their natural habitat and the best wines come from non irrigated vines. Less rain means less fungus and less spraying so it’s all good.
I want to see how sea surface temperature has evolved over the decades. The process is shown below. First copy and paste the average monthly temperature for the entire period to the head of the spreadsheet immediately adjacent and to the right of the raw data. Follow in the next row with a label for each month. In the next row calculate the difference between the raw data for a particular month and the average for that particular month for the entire period. For instance raw data for January 1948 is a temperature of 21.957°C and the average for the entire period for the month of January is 22.32128, the difference being 0.36428°C. This statistic is the ‘anomaly’ with respect to the average for the entire period.
I plot the anomaly for the period 1948-56 together with the average for that period of 9 years and you see it above. Its plain that this decade was cooler on average especially in April and May. I work through the decades.
When I get to the decade 1997-2006 I see this:
The months that were very cool in the first decade are very warm in 1987-96. The months that were slightly anomalously cool in 1948-56 are still slightly anomalously cool. This is interesting. If there is a greenhouse effect due to increasing carbon dioxide in the atmosphere why is there so small a temperature increase in spring and so large an increase in autumn over this sixty eight year period?
So, I plot the average for each decade and here it is:
It turns out that in the intervening decades, and in particular from 1957 until 1976 the first half of the year has been very much cooler than both the first and the last decade. There is very little change between the first and last decade. Much wider swings have occurred in the past. The decade 1977-86 was much warmer in spring and early summer than it is in the last decade. The decade 1997-2006 that saw some of the warmest years globally in terms of annual averages is the coolest within this particular band of latitude.
Obviously, there is a factor involved that can produce warming AND COOLING and climate change is not a one way train.
Obviously, annual averages are not the appropriate metric if we want to discover the sources of natural variation in climate. We need to focus on monthly data.
What is to come in this blog/book?
If you are genuinely interested in the question of whether man has an influence on the climate then read on. If you want to know what the sources of natural climate variation are then read on. But if you would rather engage in a ‘willing suspension of disbelief’ as most of us do when we go to the movies or to church on Sunday, and you are ideologically committed to the notion that man is responsible for climate change and are not willing to consider any other possibility then this is not the place for you. In short order you will be confronted by things that will bother you and you will become uncomfortable.
If you can look at data and ask yourself ‘why is it so’ please come along for the ride.