Climate change update by the numbers

Well you could try to retroactively repair the analogy, but I still think it’s just bad presentation, bad scientific communication.

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In my opinion, the Global Warming Community’s program is based on four beliefs. These are:
1. The global climate has been and is continuing to get hotter since the start of the industrial revolution. This warming is caused by “greenhouse gases” (GHG are mainly CO2 but also CH4, N2O, and halocarbons, etc) emitted by our industrial and agricultural societies. The warming due to GHG is a scientifically established fact based on IR radiative forcing.
2. When global warming goes above X °C over the pre-industrial average temperature, the result will be an existential catastrophe for all life on Earth, with severe climatological, ecological, agricultural, health and economic consequences for the human race. The limit of X °C can be determined by scientific and ecological studies before the temperature limit is reached.
3. The amount of GHG emissions needed to reach the X °C temperature limit can be calculated using computer General Circulation Climate Models. The amount of GHG in the atmosphere can be characterized by the concentration of Y ppmv CO2 that results in the global temperature increase of X °C.
4. To avoid the existential global warming catastrophe, a world-wide governmental agreement is required to limit every country’s GHG emissions such that the global CO2 concentration is held at or below Y ppm CO2, thus avoiding warming over X °C. Limits on a country’s GHG emissions can be achieved through governmental restrictions, regulations, subsidies and/or taxing of energy (fossil fuel and other) and of forestry and agricultural practices.

Following the spirit of Barry Brook’s “Climate change by the numbers”, in this post, items 1 and 3 are partially examined through use of 130 years of global temperature and GHG data along with 55 years of ocean temperature data. The data used is that generally accepted by the Global Warming Community and sources are referenced.

Various political bodies have weighed in on what X °C is. Two degrees Celsius is the limit set by The EU Commission in Jan 2007, by the G-8 in July 2009 and at the UN Copenhagen and Cancun meetings in Dec 2009 and 2010. Some think this is not enough, that the limit should be 1.5 °C and some think the 2°C limit is too stringent (and also unachievable).

The Worldwatch Institute’s State of the World 2009 says (page 18): “ Efforts to define acceptable limits to warming at a political level started in the European Union and among its member states. Based on the IPCC’s Second Assessment Report at the end of 1995, the European Union’s Council of Environment Ministers in 1996 called for warming to be limited to 2 °C above the preindustrial level.”

So the question is: What is the GHG or CO2 Y ppmv limit that will limit Global Warming to 2 °C?

I think the best way to answer this is to use an Excel spreadsheet to investigate the relationships between global average temperature and CO2 and GHG. This can be done by regressing temperature against CO2 (or GHG) radiative forcing. Radiative forcings are the scientifically correct approach for accounting of infra-red absorption and re-radiation by greenhouse gases. The equation for the temperature increase ΔT, °C for a radiative forcing of ΔF w/m2 is:

ΔT = λ∙ΔF °C Eqn #1
where lambda λ is the climate sensitivity parameter with units of °C/(w/m2).

For CO2 the radiative forcing for Y ppmv is:
ΔF = 5.35 ln(Y/278) w/m2 Eqn #2
where 278 is the pre-industrial CO2 concentration of 278 ppmv.

James Hansen, the noted climate researcher, has 130 years (1880 to 2010) of annual global mean temperature data on http:// data.giss.nasa.gov/ (see GISS Surface Air Temperature Analysis). The data is presented as global LOTI, the global land-ocean temperature index. LOTI is the global mean temperature anomaly from the base period 1950-1981, when the average global land-ocean surface air temperature was 14.0 °C. In 2010, the global LOTI was 0.63 °C. In 1880 it was -0.25 °C

Data for CO2 at Moana Loa Hawaii from 1959 to 2010 can be found at http://www.esrl.noaa.gov/gmd/ccgg/trends. To cover the period before 1959, Law Dome Antarctica CO2 data is available at http://www.ncdc.noaa.gov/paleo/metadata/noaa-icecore-2455.html. The 20 year smoothed CO2 data runs from before 1880 to 1978. The Law Dome and Moana Loa data overlap from 1959 thru 1978. Comparing the overlap indicates that Law Dome 20 year smoothed CO2 plus 0.7 ppmv equals Moana Loa CO2. CO2 in 1880 was 291 ppmv and in 2010 CO2 was 390 ppmv.

Entering the global temperature index and CO2 data into an Excel spreadsheet allows temperature and CO2 relationship to be explored. If one plots the temperature index vs CO2, it is possible to estimate the global LOTI at the pre-industrial concentration of 278 ppmv CO2. The LOTI found is -0.40. Therefore, to adjust LOTI to warming above pre-industrial, 0.40 °C is added to LOTI. So in 2010, the global mean temperature ΔT was 0.63 + 0.40 = 1.03 °C warmer than pre-industrial.

In the spreadsheet, the CO2 radiative forcing ΔF can be calculated from the CO2 concentration and plotted vs the ΔT temperature increase over pre-industrial (LOTI plus 0.4 °C). When the 130 years of data is regressed, the equation for ΔT is: ΔT = 0.548* ΔF-0.02 °C, with an R squared of 0.821. This is corresponds well with Eqn #1 since the constant term -0.02 is nearly zero as predicted by Eqn #1.

For a CO2 level of 450 ppmv, the ΔF is 2.58 w/m2 and the regressed CO2 radiative equation predicts a ΔT of 1.4 °C, and a ΔT of 2.0 °C for a CO2 concentration of 550 ppmv.

This approach can be extended to the greenhouse gases CH4, N2O and halocarbons by the information at http://www.esrl.noaa.gov/gmd/aggi/ . Data for atmospheric concentrations of CH4, N2O and various halogenated gases are presented, along with the radiative forcing equations for these GHG. At present, the CH4 concentration is 1800 ppb, N2O is 324 ppb compared with pre-industrial concentrations of 700 and 270 ppb respectively.

When the ΔT data is regressed against total GHG ΔF, the resulting equation is ΔT = 0.320* ΔF + 0.01 °C with an R squared of 0.817. When CO2 is 450 ppmv, CH4 is estimated at 1790 ppb and NO2 at 342 ppb with halocarbon radiative forcing of 0.34 w/m2, about what it is now. The total GHG ΔF is 3.65w/m2 and ΔT is 1.2 °C. At 550 ppmv CO2, I estimate ΔT is 1.5 °C.

One certain critique of this approach is that ΔT calculated is a then current temperature increase, and does not account for equilibrium effects of the GHG heating of Earth’s oceans. Ocean heating data for 0-700m is available at http://www.nodc.noaa.gov/OC5/3M_HEAT_Content. The methodology for including ocean heating can be found in Trenberth’s
http://www.cgd.ucar.edu/cas/Trenberth/trenberth.papers/EnergyDiagnostics09final2.pdf

When I include ocean heating effects (estimated at 0.26 w/m2 average from 1955 to 2009), then I get an equilibrium ΔTe about 10% higher than the ΔT’s estimated above.

I have purposely refrained from justifying the methodology or interpreting the results presented. I would encourage interested parties to try to do calculations similar to what I have described and compare results or critique my approach.

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