It is the contention of some (AGW proponents) that human carbon dioxide emissions are the major cause of global warming. Alternatively, natural cycles control the temperature and hence solution and exsolution of carbon dioxide into and out of the ocean, thereby controlling the atmospheric CO2 content.
To my knowledge, AGW proponents have yet to present any compelling physical evidence to support their contention. However, the alternative hypothesis has much supporting physical evidence. The latest is a new paper published in Global and Planetary Change:
The phase relation between atmospheric carbon dioxide and global temperature by Ole Humlum, Kjell Stordahl, Jan-Erik Solheim from several Norwegian Universities.
The paper abstract reads:
Using data series on atmospheric carbon dioxide and global temperatures we investigate the phase relation (leads/lags) between these for the period January 1980 to December 2011. Ice cores show atmospheric CO2 variations to lag behind atmospheric temperature changes on a century to millennium scale, but modern temperature is expected to lag changes in atmospheric CO2, as the atmospheric temperature increase since about 1975 generally is assumed to be caused by the modern increase in CO2. In our analysis we use eight well-known datasets; 1) globally averaged well-mixed marine boundary layer CO2 data, 2) HadCRUT3 surface air temperature data, 3) GISS surface air temperature data, 4) NCDC surface air temperature data, 5) HadSST2 sea surface data, 6) UAH lower troposphere temperature data series, 7) CDIAC data on release of anthropogene CO2, and 8) GWP data on volcanic eruptions.
Annual cycles are present in all datasets except 7) and 8), and to remove the influence of these we analyze 12-month averaged data. We find a high degree of co-variation between all data series except 7) and 8), but with changes in CO2 always lagging changes in temperature. The maximum positive correlation between CO2 and temperature is found for CO2 lagging 11–12 months in relation to global sea surface temperature, 9.5-10 months to global surface air temperature, and about 9 months to global lower troposphere temperature. The correlation between changes in ocean temperatures and atmospheric CO2 is high, but do not explain all observed changes.
The authors also say, “Changes in ocean temperatures appear to explain a substantial part of the observed changes in atmospheric CO2 since January 1980. CO2 released from use of fossil fuels have little influence on the observed changes in the amount of atmospheric CO2, and changes in atmospheric CO2 are not tracking changes in human emissions.”
It seems that AGW (human caused warming) proponents have a cause and effect problem. The figure below is from the cited paper. In that figure, green represents changes in CO2, blue represents change in sea surface temperature, and red is the change in global surface temperature (HADCRUT3).
Recently, Dr. S. Fred Singer wrote an editorial which said in part:
“The science of climate change is not just of academic interest, but has been leading to policies for large-scale changes in energy use and supply — with important economic consequences. The burden of proof for AGW therefore falls on those who call for such policies. They must demonstrate with reasonable certainty that human activities are causing global warming, that a future warming will produce significant economic and ecological damage, and that it would be more cost-effective to mitigate now rather than to adapt later. They must also be ready to respond to any critique of the underlying science.”
Dr. Singer also poses some questions for AGW supporters:
**Why did climate warm between 1910 and 1940?
**Why did climate cool from 1940-1975? If the cause is assumed to be aerosols, also please explain the separate trends observed in the northern and southern hemispheres and compare with climate models. This asymmetry has been a puzzle for some time.
**Why is there a step increase (temperature “jump”) in 1976-77 — and again in 2001-2002? Such jumps are not in accord with the slow, steady increase calculated by climate models.
**Why is there no pronounced warming trend since 2002?
**And finally, why no warming for night-time marine air temperatures, troposphere, and proxies in the last two decades of the 20th century — in conflict with reported land-surface temperatures? Could one admit the possibility that there might be something wrong with the land-surface data used by IPCC as “evidence” for AGW?
I have an additional question. If CO2 is such a powerful greenhouse gas and the major driver of global temperature as alleged, why does it stop rising? According to AGW hypothesis, CO2 should cause temperature to rise which would produce more water vapor (a strong greenhouse gas), and lead to an enhanced or runaway greenhouse effect which would cause even more carbon dioxide to exsolve from the ocean. But something seems to curtail each rise in carbon dioxide. The cited paper suggests that both temperature and atmospheric CO2 content is controlled by sun-driven decadal ocean cycle oscillations. If there is some influence from human carbon dioxide emissions, it is too small to be detected in the study.
For some additional perspective, I show a table below, constructed by a geologist several years ago, which shows the relative contributions to the greenhouse effect. That estimate concludes that total human contribution is just 0.28%. If that estimate is anywhere near reality, it helps explain why the researchers in the first paper cited above found “changes in atmospheric CO2 are not tracking changes in human emissions.”