I've read a few times here and elsewhere the argument that scientists were wrong about their warnings in the 70's of an impending ice age, so they may be wrong about climate change now.
I was interested because I remember watching a science programme (probably the BBC's Horizon) in the late 70's that was about the 'impending ice age' and thinking, as teenager's do, 'cool....' But I don't recall much else about the issue, as I was too busy drinking and chasing girls....
I thought I would take a few minutes to educate myself on what scientists were saying, were they wrong, and why. Here's what I found:
Climate modelling seems to have started in the most primitive way in the late nineteenth century, and through to about 1960 the concerns were about greenhouse effects and warming, since this was the most basic forcing mechanism identified from the application of chemistry to the atmosphere.
In the period 1940's to 1970s there was a period of cooling which was at odds with CO2 growth. In addition understanding grew of the changes in climate over the last 1m years or so.
These issues led modellers to look for a wider range of forcing mechanisms to explain both short-term and long-term trends.
Two forcing mechanisms proved particularly good in explaining changes - astronomical forcing for long-term trends and aerosol forcing for short-term trends.
Tracing back the 'scientists predicted cooling' comments on a sceptic website led me back to two authors, and an internet search found two papers:
First, on ice age cooling:
JD Hays, J Imbrie and NJ Shackleton, Science, v194, #4270, p1121, 1976/12/10
This paper appears to be the source for the 'scientists said an ice age was coming' claim.
I've not been able to read the paper, just commentary. However the quote below, covering its application to predicting the climate in the future, appears to be key:
Future climate. Having presented evidence that major changes in past climate were associated with variations in the geometry of the earth's orbit, we should be able to predict the trend of future climate. Such forecasts must be qualified in two ways. First, they apply only to the natural component of future climatic trends - and not to anthropogenic effects such as those due to the burning of fossil fuels. Second, they describe only the long-term trends, because they are linked to orbital variations with periods of 20,000 years and longer. Climatic oscillations at higher frequencies are not predicted.
One approach to forecasting the natural long-term climate trend is to estimate the time constants of response necessary to explain the observed phase relationships between orbital variation and climatic change, and then to use those time constants in the exponential-response model. When such a model is applied to Vernekar's (39) astronomical projections, the results indicate that the long-term trend over the next 20,000 years is towards extensive Northern Hemisphere glaciation and cooler climate (80).
To summarise, assuming no human influence an ice age can be expected to deveolop over the next 20,000 years.
Is this contention wrong?
Well, firstly not much of the 20,000 years has taken place, so it's a bit early to tell(!), but also the authors are clear that this prediction is only valid without any human intervention. Yet we have significant human intervention in a variety of forcing mechanisms.
So the sceptic contention that the prediction turned out to be false is itself a load of rubbish.
The key paper on short-term aerosol cooling appears to be this one:
Rasool and Schneider, Science, July 1971, p 138, "Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate"
This gets a lot of air time because Schneider is a leading proponent of climate change and so his 'conversion' to global warming is presented as a sign of the inconsistency and the flakiness of the climate change case.
Again, I can't find a copy of the paper on-line, but there is a fair amount of commentary
It appears that, using what would now be regarded as a simple model the paper tries to compare the effects of increases in CO2 (increasing the temperature) and aerosol (lowering the temperature) concentrations in the atmosphere.
They come to the conclusion that aerosol forcing is a much stronger influence than CO2 forcing. The conclusion is quoted on the web and reported below:
"Even if we assume that the rate of scavenging and of other removal processes for atmospheric dust [generally & confusingly used interchangably with aerosol in the article (WMC)] particles remains constant, it is still difficult to predict the rate at which global background opacity of the atmosphere will increase with increasing particulate injection by human activities. However, it is projected that man's potential to pollute will increase 6 to 8-fold in the next 50 years. If this increased rate of injection... should raise the present background opacity by a factor of 4, our calculations suggest a decrease in global temperature by as much as 3.5 oC. Such a large decrease in the average temperature of Earth, sustained over a period of few years, is believed to be sufficient to trigger an ice age. However, by that time, nuclear power may have largely replaced fossil fuels as a means of energy production."
It appears that there were a couple of critical errors in this paper, notably:
- That the calculations of the effect of anthropomorphic aerosol impact ignored the fact that the majority of aerosols occur naturally, so an 8-fold increase in man-made pollutants doesn't lead to anything like an 8-fold increase in aerosols in the atmosphere, and
- That the estimate used for the impact of increased CO2 on global temperature change is about 1/3 the level now accepted as valid.
The study says that if pollution levels had continued to grow at the rate seen in 1970 for 50 years there was a possibility of triggering an ice age. This was incorrect, due to the incorrect calculation of anthropomorphic aerosol impacts.
So climate change sceptics are right to point out that a major climate paper contained errors that invalidated the conclusion.
However, what the study did not say was that the earth is headed for an immediate ice age. It stated that if certain conditions prevailed (major increases in aerosols) then certain climate consequences (significant global cooling) could follow. The basic premise is still valid, but the calculation of effects was wrong.
It's worth saying that these errors were identified and corrected fairly rapidly within the scientific community - the 'Global 2000' report to the Carter administration gave the prevailing scientific concensus in 79/80 as for 'moderate warming'.
My little foray has been quite revealing for me in how climate science is presented - I've spotted examples of almost messianic devotion to the notion of climate change, which is concerning to a natural sceptic like me. It's also obvious that what the media say the scientists are saying is often not what the scientists actually are saying, but a greatly dramatized variant thereof.
I've also found numerous instances of downright lies being used to discredit climate change science:
For instance, take the hockey-stick controversy - do you know (I didn't) that there are a dozen different studies setting out past and predicted temperature trends from various data sets, and every single one is the same shape? It doesn't really matter the outcome of the rather arcane statistical argument ( I speak as a Maths grad) about the specific Mann graph - which incidentally seems to be going Mann's way - if you fit a model to the actual, historic data you end up with a hockey stick shape - end of.
Or take the recently-quoted '555 of 700-odd glaciers are growing, not shrinking'. Turns out the 555 is a typo for 55% made when one article was transposed to another, and the 55% itself appears to have been completely invented, since the article quoted as supporting it at the far end of the chain never existed!
My conclusion is that I would recommend everyone take a good look around before accepting any contentions from media commentary on either side of the debate.
Linkys:
http://www.climatechangeeducation.org/science/index.html
http://www.realclimate.org/index.php?p=74
http://www.scientific-alliance.com/the_debate_climate.htm
http://meteo.lcd.lu/globalwarming/
I was interested because I remember watching a science programme (probably the BBC's Horizon) in the late 70's that was about the 'impending ice age' and thinking, as teenager's do, 'cool....' But I don't recall much else about the issue, as I was too busy drinking and chasing girls....
I thought I would take a few minutes to educate myself on what scientists were saying, were they wrong, and why. Here's what I found:
Climate modelling seems to have started in the most primitive way in the late nineteenth century, and through to about 1960 the concerns were about greenhouse effects and warming, since this was the most basic forcing mechanism identified from the application of chemistry to the atmosphere.
In the period 1940's to 1970s there was a period of cooling which was at odds with CO2 growth. In addition understanding grew of the changes in climate over the last 1m years or so.
These issues led modellers to look for a wider range of forcing mechanisms to explain both short-term and long-term trends.
Two forcing mechanisms proved particularly good in explaining changes - astronomical forcing for long-term trends and aerosol forcing for short-term trends.
Tracing back the 'scientists predicted cooling' comments on a sceptic website led me back to two authors, and an internet search found two papers:
First, on ice age cooling:
JD Hays, J Imbrie and NJ Shackleton, Science, v194, #4270, p1121, 1976/12/10
This paper appears to be the source for the 'scientists said an ice age was coming' claim.
I've not been able to read the paper, just commentary. However the quote below, covering its application to predicting the climate in the future, appears to be key:
Future climate. Having presented evidence that major changes in past climate were associated with variations in the geometry of the earth's orbit, we should be able to predict the trend of future climate. Such forecasts must be qualified in two ways. First, they apply only to the natural component of future climatic trends - and not to anthropogenic effects such as those due to the burning of fossil fuels. Second, they describe only the long-term trends, because they are linked to orbital variations with periods of 20,000 years and longer. Climatic oscillations at higher frequencies are not predicted.
One approach to forecasting the natural long-term climate trend is to estimate the time constants of response necessary to explain the observed phase relationships between orbital variation and climatic change, and then to use those time constants in the exponential-response model. When such a model is applied to Vernekar's (39) astronomical projections, the results indicate that the long-term trend over the next 20,000 years is towards extensive Northern Hemisphere glaciation and cooler climate (80).
To summarise, assuming no human influence an ice age can be expected to deveolop over the next 20,000 years.
Is this contention wrong?
Well, firstly not much of the 20,000 years has taken place, so it's a bit early to tell(!), but also the authors are clear that this prediction is only valid without any human intervention. Yet we have significant human intervention in a variety of forcing mechanisms.
So the sceptic contention that the prediction turned out to be false is itself a load of rubbish.
The key paper on short-term aerosol cooling appears to be this one:
Rasool and Schneider, Science, July 1971, p 138, "Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate"
This gets a lot of air time because Schneider is a leading proponent of climate change and so his 'conversion' to global warming is presented as a sign of the inconsistency and the flakiness of the climate change case.
Again, I can't find a copy of the paper on-line, but there is a fair amount of commentary
It appears that, using what would now be regarded as a simple model the paper tries to compare the effects of increases in CO2 (increasing the temperature) and aerosol (lowering the temperature) concentrations in the atmosphere.
They come to the conclusion that aerosol forcing is a much stronger influence than CO2 forcing. The conclusion is quoted on the web and reported below:
"Even if we assume that the rate of scavenging and of other removal processes for atmospheric dust [generally & confusingly used interchangably with aerosol in the article (WMC)] particles remains constant, it is still difficult to predict the rate at which global background opacity of the atmosphere will increase with increasing particulate injection by human activities. However, it is projected that man's potential to pollute will increase 6 to 8-fold in the next 50 years. If this increased rate of injection... should raise the present background opacity by a factor of 4, our calculations suggest a decrease in global temperature by as much as 3.5 oC. Such a large decrease in the average temperature of Earth, sustained over a period of few years, is believed to be sufficient to trigger an ice age. However, by that time, nuclear power may have largely replaced fossil fuels as a means of energy production."
It appears that there were a couple of critical errors in this paper, notably:
- That the calculations of the effect of anthropomorphic aerosol impact ignored the fact that the majority of aerosols occur naturally, so an 8-fold increase in man-made pollutants doesn't lead to anything like an 8-fold increase in aerosols in the atmosphere, and
- That the estimate used for the impact of increased CO2 on global temperature change is about 1/3 the level now accepted as valid.
The study says that if pollution levels had continued to grow at the rate seen in 1970 for 50 years there was a possibility of triggering an ice age. This was incorrect, due to the incorrect calculation of anthropomorphic aerosol impacts.
So climate change sceptics are right to point out that a major climate paper contained errors that invalidated the conclusion.
However, what the study did not say was that the earth is headed for an immediate ice age. It stated that if certain conditions prevailed (major increases in aerosols) then certain climate consequences (significant global cooling) could follow. The basic premise is still valid, but the calculation of effects was wrong.
It's worth saying that these errors were identified and corrected fairly rapidly within the scientific community - the 'Global 2000' report to the Carter administration gave the prevailing scientific concensus in 79/80 as for 'moderate warming'.
My little foray has been quite revealing for me in how climate science is presented - I've spotted examples of almost messianic devotion to the notion of climate change, which is concerning to a natural sceptic like me. It's also obvious that what the media say the scientists are saying is often not what the scientists actually are saying, but a greatly dramatized variant thereof.
I've also found numerous instances of downright lies being used to discredit climate change science:
For instance, take the hockey-stick controversy - do you know (I didn't) that there are a dozen different studies setting out past and predicted temperature trends from various data sets, and every single one is the same shape? It doesn't really matter the outcome of the rather arcane statistical argument ( I speak as a Maths grad) about the specific Mann graph - which incidentally seems to be going Mann's way - if you fit a model to the actual, historic data you end up with a hockey stick shape - end of.
Or take the recently-quoted '555 of 700-odd glaciers are growing, not shrinking'. Turns out the 555 is a typo for 55% made when one article was transposed to another, and the 55% itself appears to have been completely invented, since the article quoted as supporting it at the far end of the chain never existed!
My conclusion is that I would recommend everyone take a good look around before accepting any contentions from media commentary on either side of the debate.
Linkys:
http://www.climatechangeeducation.org/science/index.html
http://www.realclimate.org/index.php?p=74
http://www.scientific-alliance.com/the_debate_climate.htm
http://meteo.lcd.lu/globalwarming/
