The pub trivia guide to global warming

JunkScience.com
August 2006

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Since 1850, about the time the Industrial Revolution really got underway and when people started seriously trying to monitor and record local temperatures, atmospheric carbon dioxide has risen from about 285 parts per million (ppmv)1 to about 380 ppmv today2.

Because various attempts at determining global mean temperature have different origin dates, mileage tends to vary but the IPCC3 quantifies the increase as 0.6 0.2 C for the Twentieth Century, which is about the same as "since 1850" since temperatures are believed to have risen to the 1870s and then fallen to the early 1900s4,5,6.

It is no surprise there is significant disagreement over the amount of warming estimated -- as James Hansen and the Goddard Institute for Space Studies explain7, there is no clear definition of what we mean by absolute surface air temperature and wide variation in the estimated mean surface temperature of the planet. As a consequence of the lack of standardization and the inherent difficulties involved in gathering data from remote locations, the best we can do estimating the global mean temperature (against which we estimate change) is 14 0.7 C or between about 56 and 58 F7 -- thus our margin of error is greater than our estimate of change.

Trends in global temperature are frequently given as "per decade" figures and there is general agreement between the GHCN-ERSST Data Set8 (1880 - 2005): Global Trend: 0.04 C/decade and HadCRUT2v Data Set9 (1870 - 2005): Global Trend: 0.05 C/decade, each yielding a result somewhat similar to the IPCC figure above.

Whether the high or low bound estimate is more likely to be correct is frequently hotly contested despite the relative enormity of the error margin and so we must look to other measurement methods for clues on the relative merit of the various datasets. Should we believe GHCN-ERSST10? Perhaps we should go with NASA's Goddard Institute for Space Studies GISS Surface Temperature Analysis11 with it's estimate of warming almost twice as large? Data assembled from radiosonde balloon records12 is a pretty fair match with HadCRUT34, GHCN-ERSST8 and HadCRUT2v9, suggesting independent corroboration via alternative methodology. As a further indication, satellite-mounted Microwave Sounding Unit (MSU) data13 matches lower-bound trends moderately well over the period of overlapping data, leaving the GISTEMP6 estimate looking anomalously high.

Earth's estimated rate of warming then is approximately one-half of one degree (C) per century (~0.005 C/year). Not all of this estimated increase is necessarily real since we have been closing rural meteorological stations throughout the satellite era (for reasons of economy since weather forecasting information is available remotely via satellite there is no need to station people in remote locations to make observations) and thus there is an increasing urban bias14 in the record.

Even if all of the estimated warming is real it still cannot be solely attributed to increasing atmospheric carbon dioxide. Estimates of net warming from increased carbon dioxide since the Industrial Revolution range from a relative high 0.17 C15 down to 0.1 C16. This is a trivial amount of warming when Earth's estimated absolute temperature is ~288 K, roughly 0.06% variation at most and certainly nothing to get excited about.

At the same time we have had observable increase in solar contribution, probably accounting for about half the estimated warming of the Twentieth Century17. We have not heard any contention regarding the coincidental cold of the Little Ice Age18 and the Maunder Minimum19, nor the increasing solar activity since20, 21, 22, 23.

We know that the warming effect of atmospheric carbon dioxide is logarithmic (meaning each additional unit has less effect than the one preceding) and estimates of warming due to increased carbon dioxide since the Industrial Revolution are really quite small. We know the sun is more active, possibly at its most active since the Holocene Climate Optimum23, 24. We also know the sun has been a significant contributor to our estimated warming15, 16, 17, 20, 21, 22, 23. The carbon emissions from fossil fuel use might have increased global mean temperature by about one-sixth of one degree, so what's with all the fuss about carbon dioxide?
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References:

  1. Historical CO2 record derived from a spline fit (20 year cutoff) of the Law Dome DE08 and DE08-2 ice cores (CDIAC)
  2. Monthly mean carbon dioxide, Mauna Loa Observatory, Hawaii (NOAA ESRL) See plot.
  3. IPCC Third Assessment Report (TAR)
  4. http://hadobs.metoffice.com/hadcrut3/diagnostics/global/nh+sh/monthly (Hadley Centre) See plot.
  5. ftp://ftp.ncdc.noaa.gov/pub/data/anomalies/monthly.land_and_ocean.90S.90N.df_1901-2000mean.dat (NCDC) See plot.
  6. http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts.txt (GISS) See plot.
  7. The Elusive Absolute Surface Air Temperature (SAT) (GISS)
  8. GCAG Time Series & Trends: GHCN-ERSST Data Set (NCDC) (WARNING -- very slow loading)
  9. GCAG Time Series & Trends: HadCRUT2v Data Set (NCDC) (WARNING -- very slow loading)
  10. The merged land air and sea surface temperature anomaly analysis, based on  the Global Historical Climatology Network (GHCN) land temperatures and the Comprehensive Ocean-Atmosphere Data Set (COADS) of SST data. (NCDC)
  11. GISS Surface Temperature Analysis (GISS)
  12. HadAT: globally gridded radiosonde temperature anomalies from 1958 to present (Hadley Centre) See plot.
  13. Information from the Global Hydrology and Climate Center, University of Alabama - Huntsville, USA. (UAH) See plot.
  14. Learning About Urban Heat Islands (Lawrence Berkeley National Laboratory)
  15. What Fraction of Global Warming is Due to the Radiative Forcing of Increased Atmospheric Concentrations of CO2? (Climate Science)
  16. Did Increasing Solar Activity Drive 20th-Century Global Warming? (CO2 Science)
  17. Phenomenological solar contribution to the 19002000 global surface warming (AGU)
  18. Little Ice Age (Wikipedia)
  19. Maunder Minimum (Wikipedia)
  20. Solar Irradiance Reconstruction (Lean, 2000) See plot.
  21. Sun more active than for a millennium (New Scientist)
  22. Sunspots more frequent now than any time for 1000 years (New Scientist)
  23. The Sun is More Active Now than Over the Last 8000 Years (Max Planck Society)
  24. Holocene Climate Optimum (Wikipedia)

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