- The temperature of the atmosphere at the surface and in higher altitude has increased since the beginning of the industrial era (BIE).
- Correlations are not causation. However, strong plausibility exists that human activities impose some global warming. Excellent correlation coefficients support this.
- The temperature sensitivity to radiative forcing induced by so-called greenhouse gases (GHG) must include the system’s feedback. The calculations presented here take into account the primary forcing due to greenhouse gases and the currently estimated feedback factors.
- Known GHGs (water vapour excluded) caused a surface temperature increase since the BIE of approximately 0.4 °C.
- The overall warming observed since the BIE is approx. 1 °C. Thus, all GHGs contribute by approx. 40% to it.
- CO2 alone contributes currently by 83% to the warming caused by all GHGs, and thus by 33% to the overall observed warming.
- Global system stability is confirmed from earth’s geological history and from its resilience observed after significant disturbances such as volcanic eruptions and ice ages.
- Des changements significatifs étaient en cours avant le début de l'ère industrielle.
- Other not specifically identified factors – that cannot be explained by GHGs – must have contributed approx. 0.6 °C to the observed temperature change since BIE. They must have a ramping or accumulative pattern and may be of natural or human origin.
- Any doubling of the CO2 concentration will cause an additional temperature increase of 0.56 °C (primary forcing before feedback implies a 0.75 °C increase).
IPCC define this as “equilibrium climate sensitivity”, to be likely in the range 1.5 °C to 4.5 °C, without presenting its calculation.
My calculations shown here cannot disagree more with this unexplained assessment.
- The feedback being negative, the climate is not going to run away as a consequence of GHG forcing, neither at 280 ppm CO2, nor at 400 ppm as today, and even not at 1000 ppm.
- The two layers atmospheric model with feedback is simplistic but respects the required energy balance around the Earth. Violation of this balance cannot be allowed beyond temporary accumulation or release of energy e.g. by the oceans.
- However, this simple model does not allow investigating neither transitory oscillations (over a few years or decades) nor geographic distribution.
- All but one of the global circulation models discussed by IPCC in its latest report are exaggerating – sometimes grossly – their calculated temperature anomalies as compared to current observations. Therefore, their validity is not established, neither to explain the current situation, nor to be used for any forecasting.
- In a do nothing scenario the temperature would increase by an additional 0.4 °C by 2047 and 1.1 °C by the end of the century (1.4 and 2.1 °C relative to BIE).
CO2 contribution to such warming would be 0.2 and 0.5 °C.
- The worst case scenario for global warming occurs for the best case economic development scenario. With a 50% more intensive use of fossil fuels than today, the additional warming could reach 0.6 °C in 2047 and 1.4 °C by the end of the century (1.6 and 2.4 °C since BIE).
- A drastic and immediate implementation of a global Kyoto-like scenario (K) would restrain the warming by 0.2 °C in 2047 or 0.5 °C at the end of the century.
In such case, the reduction of CO2 emissions could help reducing the warming by 0.09 °C in 2047 and 0.24 °C at the end of the century, as compared to the do nothing scenario A.
- Any forecast will be difficult to verify as long as no adequate disentanglement mechanism is available to distinguish causes and effects, and to filter-out disturbances. The multivariate regression analysis made in this work is a first and limited attempt.
- But no more centennial data series are available than T anomalies, counts of solar spots, Atlantic multi-decadal oscillations, and CO2 atmospheric concentration. And yet, these data have been heavily massaged to obtain useful sets. All other constructions are already the result of models based on proxies and often unscientifically tuned to obtain a desirable result. Climate studies are under a high risk of cultivating tautologies.
- All of my evaluations are certainly inaccurate and may miss important points. But no one can beat enthalpy balance and basic physical phenomena. Thus, orders of magnitude presented here are within a plausible ball park.
- Drastically reducing future carbon emissions – and hence inhibiting social and economic development as we shall see later – can barely contribute to modify the climate evolution. This is the main take home message from this first chapter.
