Global Warming--What Do We Know?

For more than a decade, I’ve  followed information and opinions about climate change.  I’ve read a lot of denial and a lot of scientific data and projections which confuse me.  But through it all, one thing that to me is solid is the NASA measured data shown below.  It’s the holy grail of climate change science for me.

http://data.giss.nasa.gov/gistemp/graphs_v3/

The data points plotted for each year are the average over the whole earth and the entire year.  “Temperature anomaly” is the difference of data points from the average in the 1951 to 1980 period which is 15 plus a few tenths degrees Centigrade (59 degrees Fahrenheit). 

Recently the Intergovernmental Panel on Climate Change (IPCC) issued its fifth Assessment Report and, as expected, there is a flood of criticism from skeptics and deniers.  It is inconceivable that one can look at the data above and deny that there has been global heating.  Skepticism on future projections?  Maybe that’s different.

But I have my own criticism from having read the “Summary for Policyholders” sub-report.  I look at the recent part of the chart above and see a definite leveling of warming.  The five year average change has been level at about 0.56 degree for four years and can be expected to stay level or slowly changing in the future because of the data points since 2001 which cluster about this average.

The IPCC report, which publishes the same chart does not acknowledge a leveling of  warming, but acknowledges a reduction in the warming rate for the period from 1998 to 2012 as compared with the period 1951 to 2012.  It does not acknowledge the flat data during 2004 through 2012 or in the periods 1880 through 1920 or 1945 through 1975.  Why not?  Could it be that these data are akin to the family with an alcoholic uncle whom they wish could just be kept out of sight?

Part of the mystery of this slowing or leveling of warming is that the increase in CO₂ in the atmosphere is on a steady rise as shown in the report.  The two do not appear to be going hand in hand as was thought at one time.  This begs for a discovery of causes other than or in addition to CO₂. 

What about long range projections?  The IPCC report states that the computer models for long range prediction have been revised and there are now four different scenarios ranging from mild to severe warming.  That seems to realistically represent the uncertainty; unfortunately it gives zealots on both sides of the issue an opportunity to pick the model that they prefer.

  

Back to the graph above.  Does the leveling of warming in the last decade mean that the great god of cooling has defeated the great god of warming and that global climate change is a thing of the past?  It would be comforting.  We wouldn’t have to use those curly light bulbs any more and we wouldn’t have to feel guilty about leaving a change in the environment for future generations.  But given the temperature rise in the last century and the higher rate of rise in the 1980s, the possibility of future warming can hardly be ignored.

Climatology is an incredibly complex science.  I believe that climate scientists are on a steep learning curve—and must be true scientists, not influenced by political agendas.