Although, I broadly agree with most of your earlier posts, this is is speculative drivel.
The warming from 1910 to 1940 is generally attributed to a variety of factors including some increase in solar irradiance, a lack of major volcanic eruptions, the rise in CO2 and other greenhouse gas levels that was already occurring, and perhaps also some internal variability. The cooling from 1940 to 1970 (which was fairly modest) is generally attributed mostly to an increase in aerosol pollutants (and this is supported by the fact that the cooling was more pronounced in the Northern Hemisphere) with some contribution from volcanic eruptions.
I suspect even you are not convinced since you use the term “generally attributed” twice. Let’s look at factors you cite for the 1910-40 warming
1. “some” solar irradiance
Leif may have something to say about that but whatever there was no decrease in solar irradiance after 1940.
2. a lack of major volcanic eruptions,
Interesting that a lack of something produces such a sustained positive forcing over several decades. However there were major eruptions in 1883 and 1902. There has not been a major eruption for since 1991 (Pinatubo) – is the warming since then related to “a lack of volcanic eruptions”?
3. perhaps also some internal variability
Love it. What does this mean? Is this the ‘catch all’ in case the solar/volcano stuff goes belly up. The IPCC has undertaken rigorous “Attribution and Detection” studies which supposedly show that the late 20th century warming can only be explained by including an increase in ghg concentrations. It now appears that there may also be some “internal variability – perhaps”.
The explanation for the 1940-70 cooling is worse.
1. There was NO increase in aerosol pollutants in the 1940s – show me the data. (**see below) 2. To explain he temperature decline between 1945 and 1951, the aerosol increase would have to be on a phenomenal scale and sustained over many years. Remember the aerosols would not only have to induce a cooling effect they would also need to reverse a strong warming trend. Aerosols are not like CO2. They are short-lived in the atmosphere. Industrial (tropospheric) aerosols are nowhere near as plentiful or effective as volcanic (stratospheric) aerosols. 3. The effect of aerosols is regionally specific. There is some dispersal but they get “rained out” fairly quickly. 4. Between 1940 and 1970 – the Arctic cooled at 4 times the rate of the NH in general. How did this happen? See GISS zonal data. Note that the arctic also warmed at 4 times the rate of the NH in the 1910-40 period (again see GISS zonal data). And guess what happened between 1970 and 2000 ……? 5. Aerosols which do eventually find their way to the arctic actually produce warming due to the arctic haze effect (http://en.wikipedia.org/wiki/Arctic_haze ) 6. If aerosols did cool the arctic there should be a strong seasonal signal, i.e. aerosols can only reflect sunlight when the sun is shining. Between Sept and March their effect would be non-existent.
** Re: aerosol data. There is very little before ~1970. However we can probably get a rough estimate of any change in aerosol production from proxy data – namely CO2 emissions. Between 1920 and 1950 global CO2 emissions were broadly flat.
In a nutshell. No-one can explain the the early 20th century warming or mid-20th century cooling – and probably not the late 20th century warming either. Internal variability, including ocean oscillations, is probably the most likely candidate for the fluctuations with CO2 a possible candidate for the weak underlying trend.
Joel Shore (19:05:40) :
Although, I broadly agree with most of your earlier posts, this is is speculative drivel.
The warming from 1910 to 1940 is generally attributed to a variety of factors including some increase in solar irradiance, a lack of major volcanic eruptions, the rise in CO2 and other greenhouse gas levels that was already occurring, and perhaps also some internal variability. The cooling from 1940 to 1970 (which was fairly modest) is generally attributed mostly to an increase in aerosol pollutants (and this is supported by the fact that the cooling was more pronounced in the Northern Hemisphere) with some contribution from volcanic eruptions.
I suspect even you are not convinced since you use the term “generally attributed” twice. Let’s look at factors you cite for the 1910-40 warming
1. “some” solar irradiance
Leif may have something to say about that but whatever there was no decrease in solar irradiance after 1940.
2. a lack of major volcanic eruptions,
Interesting that a lack of something produces such a sustained positive forcing over several decades. However there were major eruptions in 1883 and 1902. There has not been a major eruption for since 1991 (Pinatubo) – is the warming since then related to “a lack of volcanic eruptions”?
3. perhaps also some internal variability
Love it. What does this mean? Is this the ‘catch all’ in case the solar/volcano stuff goes belly up. The IPCC has undertaken rigorous “Attribution and Detection” studies which supposedly show that the late 20th century warming can only be explained by including an increase in ghg concentrations. It now appears that there may also be some “internal variability – perhaps”.
The explanation for the 1940-70 cooling is worse.
1. There was NO increase in aerosol pollutants in the 1940s – show me the data. (**see below)
2. To explain he temperature decline between 1945 and 1951, the aerosol increase would have to be on a phenomenal scale and sustained over many years. Remember the aerosols would not only have to induce a cooling effect they would also need to reverse a strong warming trend. Aerosols are not like CO2. They are short-lived in the atmosphere. Industrial (tropospheric) aerosols are nowhere near as plentiful or effective as volcanic (stratospheric) aerosols.
3. The effect of aerosols is regionally specific. There is some dispersal but they get “rained out” fairly quickly.
4. Between 1940 and 1970 – the Arctic cooled at 4 times the rate of the NH in general. How did this happen? See GISS zonal data. Note that the arctic also warmed at 4 times the rate of the NH in the 1910-40 period (again see GISS zonal data). And guess what happened between 1970 and 2000 ……?
5. Aerosols which do eventually find their way to the arctic actually produce warming due to the arctic haze effect (http://en.wikipedia.org/wiki/Arctic_haze )
6. If aerosols did cool the arctic there should be a strong seasonal signal, i.e. aerosols can only reflect sunlight when the sun is shining. Between Sept and March their effect would be non-existent.
** Re: aerosol data. There is very little before ~1970. However we can probably get a rough estimate of any change in aerosol production from proxy data – namely CO2 emissions. Between 1920 and 1950 global CO2 emissions were broadly flat.
In a nutshell. No-one can explain the the early 20th century warming or mid-20th century cooling – and probably not the late 20th century warming either. Internal variability, including ocean oscillations, is probably the most likely candidate for the fluctuations with CO2 a possible candidate for the weak underlying trend.