We have shown that anthropogenic forcings do not polyno mially cointegrate with

We have shown that anthropogenic forcings do not

This preview shows page 29 - 30 out of 46 pages.

We have shown that anthropogenic forcings do not polyno- mially cointegrate with global temperature and solar irradi- ance. Therefore, data for 1880–2007 do not support the an- thropogenic interpretation of global warming during this pe- riod . This key result is shown graphically in Fig. 3 where the vertical axis measures the component of global temper- ature that is unexplained by solar irradiance according to our estimates. In panel a the horizontal axis measures the anomaly in the anthropogenic trend when the latter is derived from forcings of carbon dioxide, methane and nitrous oxide. In panel b the horizontal axis measures this anthropogenic anomaly when apart from these greenhouse gas forcings, it includes tropospheric aerosols and black carbon. Panels a and b both show that there is no relationship between tem- perature and the anthropogenic anomaly, once the warming effect of solar irradiance is taken into consideration. However, we find that greenhouse gas forcings might have a temporary effect on global temperature . This result is il- lustrated in panel c of Fig. 3 in which the horizontal axis measures the change in the estimated anthropogenic trend. Panel c clearly shows that there is a positive relationship between temperature and the change in the anthropogenic anomaly once the warming effect of solar irradiance is taken into consideration. Currently, most of the evidence supporting AGW the- ory is obtained by calibration methods and the simulation of GCMs. Calibration shows , e.g. Crowley (2000), that to explain the increase in temperature in the 20th century, and especially since 1970, it is necessary to specify a sufficiently strong anthropogenic effect. However, calibrators do not re- port tests for the statistical significance of this effect, nor do they check whether the effect is spurious 12. The implication of our results is that the permanent effect is not statistically significant . Nevertheless, there seems to be a temporary an- thropogenic effect. If the effect is temporary rather than per- manent , a doubling , say, of carbon emissions would have no long-run effect on Earth’s temperature, but it would in- crease it temporarily for some decades . Indeed, the increase in temperature during 1975–1995 and its subsequent stabil- ity are in our view related in this way to the acceleration in carbon emissions during the second half of the 20th century (Fig. 2). The policy implications of this result are major since an effect which is temporary is less serious than one that is permanent .The fact that since the mid 19th century Earth’s tempera- ture is unrelated to anthropogenic forcings does not contra- vene the laws of thermodynamics, greenhouse theory, or any other physical theory. Given the complexity of Earth’s cli- mate, and our incomplete understanding of it, it is difficult to attribute to carbon emissions and other anthropogenic phe- nomena the main cause for global warming in the 20th cen- tury.
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