Many of you may be wondering what justification we have for believing that global warming is occurring.
That's what this post will attempt to explain: the reasoning behind the assumption that the Earth is warming.
We have direct measurements of quasi-global temperature going back to about 1850 or so.1
In Central England we have records going back to 1659, the furthest far back instrumental records go.2
From 1850 to about 1940 we measured, on average, an increase in global temperatures; from 1940-1970 a cooling and from 1970 onwards a heating again.3
This can be shown in a graph, like so:
This is a graph from the BBC, by the way; in future I'll try to make my own.
It can be seen quite clearly that, on average, temperatures have increased.
However, climate is a long-term thing; a mere century and a half of data isn't really evidence enough.
We have indirect measurements of temperature going back around eight hundred thousand years, however, contained in the ice cores of Antarctica.4
Here is a graph showing temperature deviation from the average going back four hundred thousand years.
It was created by James Hansen of NASA.
So nothing special, you might say. Temperatures have been higher in the past than they are now.
Except that we haven't taken into account rate of change.
Within the past century and a half average temperatures have risen by 0.76 degrees Celsius. 5
This is an unprecedented rate.
Something must be causing it, and that's what we'll come back to in the next post.
References:
1. http://en.wikipedia.org/wiki/Instrumental_temperature_record
2. http://hadobs.metoffice.com/hadcet/
3. http://en.wikipedia.org/wiki/Instrumental_temperature_record#Warming_in_the_instrumental_temperature_record
4. http://www.esf.org/activities/research-networking-programmes/life-earth-and-environmental-sciences-lesc/completed-esf-research-networking-programmes-in-life-earth-and-environmental-sciences/european-project-for-ice-coring-in-antarctica-epica-page-1.html
5. http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf
That's what this post will attempt to explain: the reasoning behind the assumption that the Earth is warming.
We have direct measurements of quasi-global temperature going back to about 1850 or so.1
In Central England we have records going back to 1659, the furthest far back instrumental records go.2
From 1850 to about 1940 we measured, on average, an increase in global temperatures; from 1940-1970 a cooling and from 1970 onwards a heating again.3
This can be shown in a graph, like so:
This is a graph from the BBC, by the way; in future I'll try to make my own.
It can be seen quite clearly that, on average, temperatures have increased.
However, climate is a long-term thing; a mere century and a half of data isn't really evidence enough.
We have indirect measurements of temperature going back around eight hundred thousand years, however, contained in the ice cores of Antarctica.4
Here is a graph showing temperature deviation from the average going back four hundred thousand years.
It was created by James Hansen of NASA.
So nothing special, you might say. Temperatures have been higher in the past than they are now.
Except that we haven't taken into account rate of change.
Within the past century and a half average temperatures have risen by 0.76 degrees Celsius. 5
This is an unprecedented rate.
Something must be causing it, and that's what we'll come back to in the next post.
References:
1. http://en.wikipedia.org/wiki/Instrumental_temperature_record
2. http://hadobs.metoffice.com/hadcet/
3. http://en.wikipedia.org/wiki/Instrumental_temperature_record#Warming_in_the_instrumental_temperature_record
4. http://www.esf.org/activities/research-networking-programmes/life-earth-and-environmental-sciences-lesc/completed-esf-research-networking-programmes-in-life-earth-and-environmental-sciences/european-project-for-ice-coring-in-antarctica-epica-page-1.html
5. http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf
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