Latest data on global warming

With all the data in for 2012 I have been looking at the latest figures on global warming. I've been looking forward to doing this since my posts last September in response to a speech by Nigel Lawson.

Here is basic picture since 1970 according to the three main datasets:-

The data shown here are not quite raw - to make the comparison between the three datasets, I rebased the anomalies so that the average anomaly for the period 1970-2012 for each dataset was the same as for the NOAA set, where they are differences from the estimated average surface temperature over the 20th Century.

A strong upward trend is visible over the whole period, but some flattening off is apparent over the past few years - to the delight of the Global Warming Policy Foundation.

Here are the past 16 years:-

On this subset, the upward trend is hardly visible. In fact, the trend over the 16 years is around 0.005 deg C per year, which, if continued, would imply 0.5 degrees of warming over a century. ("Trend", in this context, is the slope of the regression line calculated by ordinary least squares.)

0.5 degrees over a century may not seem very much but, of course, with CO2 still being pumped into the atmosphere, we can expect the rate of temperature rise to increase.

Here is a graph showing the 16-year trend calculated for each year back to 1970:-

As can be seen, the 16-year trend has varied a lot in recent years - peaking at about 0.025 degrees in 2007. It is now exceptionally low - lower than it has ever been since the late 1970s.

I picked 16 years as the span of the trend because that is what recent controversy has been about. What if I had used a different number of years over which to calculate the trend? The next graph gives the answer for 2012:-

As can be seen, the trend is actually negative for periods of 10 and 11 years but for 20 years or more it is around 0.015 degrees per year, or 1.5 degrees over a century.

Another way to look at the data is simply to compare one decade with another. This is what we get when we look at the last four decades:-

 When we look at whole decades at a time, the rise in temperature looks pretty constant. If we look just at the differences between the decades, we find that it actually has been pretty constant:-

with the decade to 2002 showing a slightly bigger increase over the previous decade than the other two.

So what does all this mean? Well, this is just an update. I said all I wanted to say in my post on this subject back in September.

The datasets can be download here:-

GISTEMP
NOAA
HADCRUT4

See also an interesting commentary on the latest data, by James Hansen et al.