Posts Tagged ‘IPCC’

Is the global temperature ‘hiatus’ significant?

October 4, 2013
The 'anomaly' of the air temperature above the land surfaces of the Earth. The area highlighted at the top right shows temperature estimates in recent years. The 'zero' corresponds to the average value between 1961 and 1990.

The ‘anomaly’ of the air temperature above the land surfaces of the Earth. The area highlighted at the top right shows temperature estimates in recent years. The ‘zero’ corresponds to the average value between 1961 and 1990.

Much of the media discussion about last week’s Fifth Assessment Report of the Intergovernmental Panel on Climate Change centred on the ‘slowdown’ in the rate of rise of Global Mean Temperature. This was held up by sceptics as evidence that climate models were unreliable.

While preparing for a forthcoming conference, I re-plotted the data for the temperature rise above the land surfaces of the Earth and took a close look at the graph. I was shocked at just how insignificant this ‘temperature hiatus’ appeared to be. You can judge its significance for yourself. The ‘details’ section below has … wait for it… ‘detailed information’ about the data.

The black dots represent the best estimate of the ‘anomaly’ for each year. i.e. the difference from the average value between 1961 and 1990. The red lines join the dots to give an unbiased impression of ‘trend’. The grey bars above and below each point show the range of values within which the team at the Climate Research Unit are confident that the true value lies.

After recovering from my surprise I had three thoughts:

  • My first thought was to reflect that when we discuss this issue in Protons for Breakfast we pay almost no attention to this data. Although the graph is iconic it really is not part of the main discussion. In fact it is really a triumph of scientific endeavour that we have managed to reconstruct it all!
  • My second thought was how interesting it was that  sceptics have moved on from saying this graph is unbelievable because it is based on unreliable data and analyses. Now they say they believe it and find significance in essentially random details that support their view that climate science is somehow ‘wrong’.
  • My third thought was to wonder what will happen next: And of course the answer is “we don’t know” – its the future, and climate is complicated.

But whether you can see a ‘hiatus’ in this data or not, it is clear that rate of temperature change is much slower than the rate at which governments change, but still fast enough to be significant within a single lifetime. Even for a 53 year-old like me.

Details

The data plotted is from the so-called CRUTEM3 analysis of land surface temperatures. The ‘CRU’ refers to the Climatic Research Unit of East Anglia University. The  ‘TEM’ refers to temperature and the ‘3’ is the version number.

CRUTEM3 is an analysis of historical meteorological data of the air temperature approximately one metre above the land surfaces of the Earth.  The input to the analysis are thousands of data series from individual meterological stations. The analysis searches for errors in these series (and there are lots!) and attempts to find trends in the data.

You can download the data from this page of the Met Office Web SIte. This page also has an analysis of the sea surface temperatures, and the combined sea and land surfaces of the Earth.

Downloading and plotting graphs can be tricky because the data is in a very basic format (described here) but it is interesting. The data are archived in this primitive form in order to keep them universally accessible. However if you prefer to look at the data using a  commercial spreadsheet, you can download the spreadsheet (.xslx) into which I put the data here: CRUTEM 3 Anomaly.

Is the IPCC report ‘News’?

September 27, 2013
For a couple of hours this was the headline at the BBC News Web Site. By the evening it was the fourth story after a 'Tax Break for Married Couples'.

For a couple of hours this was the headline at the BBC News Web Site. By the evening it was the fourth story after a ‘Tax Break for Married Couples’.

Why do I find myself unmoved by the release of the fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC)? Because despite the epic scale of the report, on my quick perusal of the summary, I see nothing ‘new’.

And the BBC seems to concur. Although it made the lead story on the BBC web site for a couple of hours, it was down to fourth position by the evening and made only the third story on the television news. At least it was ahead of the inane story about why ballet dancers don’t get dizzy. [Aside: since when was that considered ‘News’?].

One aspect of the news did make me smile. Because of the ‘pause’ in rise of the average air temperature above the land surfaces of the Earth, sceptics are now saying that our understanding of climate change must be fundamentally flawed. This made me smile because while the ‘temperature curve’ was rising the sceptics were arguing that the data could not be relied upon. Now that it has slowed down, the data is all of a sudden more trustworthy!

But levity aside  the report is grim. It reads like a list of battle casualties where new intelligence reveals that those previously listed as ‘missing in action’ are now confirmed as ‘fatalities’ or ‘injured’. The report list each casualty detailing our state of knowledge of the extent of their injury. I have included a couple of snippets below.

So the report is as clear as it can be, but it leaves one basic question unasked, and of course unanswered:

What are we going to do about all this?

Snippets

  • The atmospheric concentrations of carbon dioxide (CO2), methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years.

  • CO2 concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions.

  • The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification

  • Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent (high confidence)

  • Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence). It is virtually certain that the upper ocean (0−700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971.

  • Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years (medium confidence). 

  • The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence). Over the period 1901–2010, global mean sea level rose by 0.19 [0.17 to 0.21] m


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