Guest essay by Sheldon Walker – (agree-to-disagree.com)
The central objective of the Paris Agreement is its long-term temperature goal to hold global average temperature increase to “well below 2°C above preindustrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels”.
Below, is an explanation of the different elements of this bar chart.
This bar chart contains a lot of information. Take your time, and study it carefully. You will find a lot of interesting data. The points listed below will help you to get the most out of this bar chart.
This bar chart was made, using the GISTEMP gridded temperature series (Land-Ocean Temperature Index, ERSSTv5, 1200km smoothing).
The bar chart contains information about 8 latitude bands. There is a map of the world at the end of this article, which shows the area of the Earth for each latitude band. From left to right these are:
· 90N to 66N – [the Arctic] – approximately 4% of the Earth
· 66N to 38N – approximately 15% of the Earth
· 38N to 18N – approximately 15% of the Earth
· 18N to Equ – approximately 15% of the Earth
· Equ to 18S – approximately 15% of the Earth
· 18S to 38S – approximately 15% of the Earth
· 38S to 66S – approximately 15% of the Earth
· 66S to 90S – [the Antarctic] – approximately 4% of the Earth
The 2 outside bars are for the Arctic (on the left), and the Antarctic (on the right). These outside bars are narrower than the inside bars, because they represent a smaller area of the Earth, than the inside bars. The outside latitude bands each represent about 4% of the Earth, compared to the inside latitude bands, which each represent about 15% of the Earth. The outside bars are therefore about 1/4 of the width of the inside bars.
The areas of all bars, and all parts of bars, is proportional to the corresponding area of the Earth. You can therefore compare any areas, and even combine different areas, and get an accurate reflection of the real Earth.
The inside latitude bands are split into 2 bars, Land on the left, and Ocean on the right. You can see from the relative heights of each pair of bars (Land and Ocean), how much of that latitude band is made up of Land, and how much is made up of Ocean.
There are 5 temperature categories. Each temperature category shows how much the “theoretical” temperature has increased, since 1880. These are:
· red – the temperature has increased by more than 2.0 degrees Celsius
· orange – the temperature has increased by between 1.5 and 2.0 degrees Celsius
· yellow – the temperature has increased by between 1.0 and 1.5 degrees Celsius
· green – the temperature has increased by between 0.0 and 1.0 degrees Celsius
· blue – the temperature has increased by less than 0.0 degrees Celsius (i.e. the temperature has cooled)
Red and orange can be used to see how much of each latitude band is above the IPCC’s temperature targets, of 1.5 and 2.0 degrees Celsius.
Yellow, green, and blue are all below the temperature target of 1.5 degrees Celsius. However, yellow can be used to see how much of each latitude band is near the 1.5 degrees Celsius temperate target.
All percentages which are read off the Y-axis of the bar chart, are the percentage of the latitude band. However, you can easily estimate the percentage of the Land, or the percentage of the Ocean, by estimating the proportion that a coloured region takes up, of a particular bar. For example:
· The Land bar, of the 38N to 18N latitude band, goes up to about 40% on the Y-axis.
· Green, yellow, and orange go up to about 10%, 30%, and 40% on the Y-axis.
· So we can estimate that green is about 25% of the land bar, yellow is about 50% of the land bar, and orange is about 25% of the land bar.
· The small (1% to 2%) red area has been ignored in the calculation.
Land is anything between the 66N line of latitude, and the 66S line of latitude, where you can stand without getting your feet wet. Land is approximately 26% of the Earth.
Ocean, is anything between the 66N line of latitude, and the 66S line of latitude, where your feet get wet, if you stand there. Ocean is approximately 66% of the Earth.
To determine which 2 x 2 latitude-longitude cells were Land, and which were Ocean, I digitised a big black and white map of the world. This turned the image into 0’s and 1’s, depending on the colour on the map. 1’s corresponded to Land, and 0’s corresponded to ocean. This might not be perfect, but it looked good, and was much faster than doing it manually.
You can judge for yourself, how good my method was, for working out what was Land, and what was Ocean. The following map shows the areas that I used for each region.
The legend is:
• yellow = Arctic region
• green = Antarctic region
• blue = Ocean
• orange = Land