In this post, I’m going to look at the modern temperature record (1880-2014) and whether the only cause for the recent warming is CO2. There are several sources for temperature data, the most common are HadCRU, GISS, BEST, RSS and UAH. The first 3 are ground-based measurements, which vary in how they calculate global temperature. The last two are satellite measurements.
Each dataset has its nuances. For instance, the HadCRU datasets do not cover the poles, as there is no data in those areas. GISS extrapolates across the poles to get 100% coverage. Which is right? Who knows, and it really doesn’t matter as long as you don’t try to compare across the models but look at the trends internal to each. So we’ll only be looking at trends.
Each of the datasets are available on the internet. I will be using the HadCRU dataset and the UAH dataset, to compare ground based measurements vs. satellite measurements. Why HadCRU? Because by limiting the sets to measured data rather than interpolated data at the poles, the likelihood of introduction of biases is reduced.
Here is the plot of the HadCRU dataset:
As you can easily see, there are major trends visible in the HadCRUT4 data. From 1880 through 1910, temperatures were level or slightly falling. 1910-1940 saw a significant temperature rise. 1940-1975 were level or falling and from 1975-2000 temperatures rose. After 2000, temperatures remained constant. We will talk about this apparent plateau in depth later in this article.
According to the AGW theory, CO2 could only have affected the years after 1975. Before that, CO2 levels were too low to affect temperature in any meaningful way. Therefore, the warming in the 1910-1940 timeframe was natural. Here is a plot of that timeframe along with a linear trend of the temperatures:
As you can see, the trend is a rise of .0134°C/year, or 1.34°C/ century. Now let’s look at the trend from 1979-2001:
The trend over this timeframe is 1.65°C/century. Note, if you dismiss the current temperature plateau as a plateau, and we include it in the analysis, the trend is 1.58°C/century. This clearly shows that there is almost no difference in the rate of warming that was seen in the first half of the 20th century (purely natural) and the warming in the last quarter. The AGW theory says this warming was solely due to CO2, which I (and others) contend is a mix of CO2 and natural causes.
Since the UAH dataset is satellite based, the dataset is much shorter. Here’s the dataset:
As is clear, there are some major characteristics of this dataset. First, 1980-1995 show mostly constant temperatures. 1995-2001 shows an almost step increase in temperatures. After 2002 temperatures were once again constant. If we take a linear trend of this timeframe, the trend is 1.39°C/century
The next plot shows the UAH and HadCRU datasets on the same plot (limiting the years to 1980-2014):
As you can see from this plot, the UAH and HadCRU datasets diverge rather dramatically from 1979-1995. The rapid rise in UAH curve from 1995-2001 closes that gap, but from 2001 on, the temperatures are constant and similar. The last part reinforces that the current temperatures are in a plateau and are not warming in any significant way. Let’s now look at these last 12 years in depth:
As can easily be seen, the temperature rise since 2001 has been very minimal. In fact, the HadCRU dataset shows a rise rate of only 0.2°C/century. The UAH shows a trend of 0.6°C/century. Neither of these temperature rises could possibly be considered dangerous.
One last point to make, altho this one isn’t quite as solid as the above. Recent years have shown the GISS, and HadCRU datasets to have been adjusted. While the purveyors of this adjusting claim high intentions, what these adjustments have done is raise the current temperature and lower the past temperatures, thus creating a warming due solely to these adjustments. Here is a plot showing the 199 GISS dataset for the US to the 2012 GISS dataset:
The next plot is the average additions/subtractions made to the raw data across the years. As you can clearly see, the past has been cooled and the present has been warmed.
Are these adjustments reasonable? I do not know, but a skeptical person would wonder what people are trying to sell that required such drastic adjustments. Note that these adjustments are almost 40% of the total temperature rise since 1880!
So in summary, this short analysis has shown the following: 1) temperatures have been rising for the last 150 years, and have risen about 0.8°C. In that time, two separate warming events caused all of this warming: 1910-1940 and 1975-2000. Since 2000, however, there has been no appreciable warming. In the current AGW studies, this timeframe is called the “hiatus” and climatologists have no clear explanation for it as all of the climate models say that this hiatus can’t happen with the rising CO2 that we are witnessing.