Nar--, el aporte de CO2 de origen humano es pequeño en relación con el aporte anual total a la atmósfera, pero vuelvo a repetir, no es eso lo más importante, si no el equilibrio entre lo que se absorbe y se aporta, equilibrio que estamos rompiendo.
En cuanto a glaciaciones anteriores o períodos con una temperatura mayor pueden explicarse porque la concentración de CO2 no es el único motivo por el cual la temperatura en la tierra pueda modificarse. Hay muchos otros como la actividad solar, la formación de aerosoles en la tierra (como por ejemplo con los volcanes o la contaminación), la composición de gases en la atmósfera etc que influyen.
No puedo decirte si es bueno o malo usar azufre para bajar la temperatura mdia de la tierra, pues no sabemos como nos puede salir el tiro si bien o muy mal pero a este paso seguramente algo habrá que hacer. yo voto por utilizar energía de fuentes renovables lo primero.
Saludos
Climate simulations were run using two natural factors that drive climate - volcanoes and the sun. Volcanic eruptions cool global temperature for a few years after eruption. A drop in volcanic activity after 1915 contributed slight warming in the early 20th Century. However, the greater contributor to warming from 1880 came from the sun which steadily warmed up to the 1940s. When the two factors are combined, they account well for the warming from 1880 to 1940. However, the contribution from sun and volcanoes to global temperature since the 1940s has been a slight cooling effect.
Figure 1: Climate model results from natural forcings compared to observations (black line). The red line is the average of the four-member ensemble. The pink shading is the model range. The blue line is the ensemble miccionan and the light blue shading is the ensemble range.
To calculate the human influence on climate, three forcings were considered: ozone, sulfate aerosols and man-made greenhouse gases. Sulfate aerosols have a cooling effect, growing stronger after around 1950. Changes in ozone produced a slight warming response. The strongest effect is from greenhouse gases which produced slow warming in the early 20th Century, then accelerated in the 1970s. When all anthropogenic forcings are combined, they show little temperature response from 1880 to to the 1960s. They do a poor job of explaining the warming from 1880 but a very good job of capturing late 20th Century warming.
Figure 2: Climate model results from anthropogenic forcings compared to observations (black line).
When natural and anthropogenic forcings are combined, they show close correspondance with global temperature. From this analysis, Meehl concludes that the warming from 1880 to the mid-20th Century was largely natural with the sun being the main contributor. Late 20th Century warming after 1970 is mainly due to man-made influence primarily from greenhouse gases.
Figure 3: Climate model results from natural + anthropogenic forcings compared to observations (black line).
This analysis is a useful reminder that CO2 is not the only driver of climate. To end the Little Ice Age, the sun did most of the early heavy lifting. When the solar contribution flattened out in the mid-20th century, humanity took the baton and we've been running with it ever since. Meehl 2004 is also confirmation that past climate change tells us how sensitive climate is to radiative forcing. The climate that responded to the forcing from the warming sun in the early 20th century is the same climate that is now responding to the forcing from rising greenhouse gases.
What ended the Little Ice Age?
