When one looks at climate change by latitude there is diversity in the warming/cooling according to the time of year. The interest in this chapter is to ascertain if there is a generalised warming that is like a groundswell, underpinning the whole. That is what would be expected under the greenhouse scenario.
Surface air temperature data for the globe as a whole is available via reanalysis. We need data for the populated and the underpopulated parts of the globe and for all the parts where no man lives.It can be found here: http://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl
From chapter 8 we are aware that inter-annual temperature variability is strongest in January and February between the Arctic and 30° south. South of that latitude temperature variability is strongest in July and August. That pulse is regular as a heartbeat and it moves surface temperature in both directions, both warming and cooling. The most extreme inter-annual variation exceeds the degree of change over the period of record. It plainly reflects non anthropogenic factors at work because the anthropogenic effect by its nature can only increase temperature, never reduce it.
In this chapter we look at temperature change by the decade. We have almost seven decades of data in the reanalysis record. Below is a summary of change between the first (1948-56) and the last period (2007-15).
60-90°North: An increase in surface air temperature in December (2.72°C) that is six times the increase in June.
30-60°North: An increase in November (0.75°C) that is more than six times the increase in February.
0-30°North: An increase in October (0.84) that is 2.4 times the increase in January.
0-30°South: An increase in April (0.84°C) that is 1.6 times the increase in August.
30-60° South: An increase in April (0.8°C) that is 2.5 times the increase in December.
60-90° South: An increase in August of 3.4°C and a decline of 1.9°C in December.
Below is the data by latitude. All diagrams are drawn with a scale of 5°C on the left axis to make them comparable. There are two diagrams for each latitude band. The lower diagram shows the difference between the first and the last periods for each month of the year. Note that the first decade is not always the coolest decade. Note also that the first and last periods include nine years while the intervening periods are of 10 years duration.
Confounding all expectations we have cooling in summer in the Antarctic. The Antarctic is characterized by temperatures below zero all year round. It contains the vast bulk of the Earth’s frozen water. Plainly that ice is in no danger of melting.
A QUESTION OF ATTRIBUTION
There are some people who attribute the entire gamut of temperature variation at the surface of the Earth to the enhancement by man of the supposed ‘Greenhouse Effect’. But we know that temperature varies with the season of the year and for any season from one year to another. The enhanced greenhouse effect can not account for cooler seasons or cooler decades.The enhanced greenhouse effect causes warming, not cooling.
It is increasingly acknowledged that the calculated temperature of the globe has not advanced since 1998, a feature variously described as ‘The Pause’ or ‘The Hiatus’. This is attributed to ‘natural cycles of unknown origin’ that are temporarily hiding the anthropogenic effect that is expected to come roaring back with a vengeance.
If we assume that the atmosphere imposes an actual ‘greenhouse effect’ via back radiation, and that it is somehow responsible for the elevation of the temperature of the surface of the Earth to some degree above that due to the direct warming via solar radiation, then how much of the increase in temperature can we attribute to the anthropogenic enhancement of this supposed natural greenhouse effect? Is there a background level of warming in every month of the year?
Greenhouse gases of anthropogenic origin are well mixed and should promote a generalized warming at all latitudes in every month of the year.
By latitude we have the strongest warming :
60-90°north. In winter
30-60°north: In spring and autumn.
0-30°north: In summer and autumn.
0-30° south: In autumn.
30-60°south: In winter.
60-90° south: In winter
If the greenhouse effect relies upon amplification via an increase in atmospheric water vapour at a particular time of the year it might be argued that the heating effect should appear at that time of the year when atmospheric moisture levels are most enhanced. We know that atmospheric humidity and global cloud cover peaks in January. The Earth as a whole is coolest in January. It is very doubtful therefore that an increase in atmospheric moisture could cause surface warming because its prime effect is to enhance cloud cover.
If the anthropogenic greenhouse effect is to promote warming then the back radiation effect would have to be more powerful than the ‘enhanced cloud cover effect’. Clouds can curtail solar radiation by as much as 90%. The clincher is that the Earth is at its coolest when atmospheric humidity (and cloud cover) peaks.
In low and mid latitudes we see warming in spring, autumn and summer but the change is tiny by comparison with high latitudes.
High latitudes have uniformly dry air and water vapour is not available as an amplifier at any time of the year. And yet this is where we see the greatest warming. And this warming is in winter when both incoming solar radiation and outgoing long wave radiation are at a minimum. It is an anachronism that the poles have warmed in winter rather than in summer.This points strongly to another warming mode that is capable of warming the air in the absence of solar radiation. The temperature at the surface is a function of surface pressure that determines whether it is warm air from the mid latitudes that makes its way into high latitudes or not. That’s a matter of simple atmospheric dynamics, which way the air is moving and where its coming from. That depends on the ozone content in the upper portion of the atmospheric column.
The warming of the poles in winter, the cooling in the Arctic in the middle decades, the marked cooling in Antarctic summer and ‘The Hiatus’ all separately and together indicate that some other mode of climate variation is very much more influential than the anthropogenic mode.
Unless we know what that ‘other mode of climate variation’ is and can account for it properly, we make an error in logic if we suggest that an average temperature for the globe as a whole is a statistic of interest or that change in that average should be a matter of concern.
Today’s climate scientists do not know what is behind the changes in temperature that are most obvious…the supposed natural climate variation.
If perchance there is someone out there who thinks differently can I ask them what they think the anthropogenic contribution has been?
Other questions spring to mind:
- Is the anthropogenic contribution just that part (or perhaps the whole) of the temperature increase in the month where the temperature increase has been least?
- Any ideas as to why surface temperature declined in Antarctica between November and February?
- Any reason for the three decade collapse in surface temperature in summer in the 30-60°north latitude band after 1948-56?
- Any ideas as to why we have this hiatus in the advance of the average global temperature since 1998?
- If the Arctic began to cool in winter and drove down the global temperature statistic at a time when habitable latitudes began to warm strongly would the global temperature statistic be an appropriate metric to assess the suitability of surface temperature to the needs of future generations of humanity?
When quite plainly there are powerful non anthropogenic forces that drive change differently according to latitude and time of year, should we have any interest at all in calculating a global temperature statistic?
Given that parts of the globe are undesirably and dangerously cold and warming is desirable, why not exclude these parts from the metric employed to indicate undesirable warming?
Could it be that the entire temperature record might be explained in terms of a natural cycle involving changes in ozone, shifts of atmospheric mass between high and other latitudes and the associated change in cloud cover?