Global Warming’s Pause for Thought – Black and White Aerosols

Climate Resistance – Global Warming’s Pause for Thought

Black and white aerosols show

The trouble is that there remains little empirical evidence to support the idea (that the period of “global cooling” between 1940 and 1970 was caused by industrial emissions of sulphate pollutants, which tend to reflect sunlight) as we were surprised to find out when we talked to UC San Diego atmospheric physicist Veerabhadran Ramanathan about his research showing that another type of aerosol – black carbon – had a significant warming effect:

Climate Resistance: What are the implications of this work for the idea that the post-war temperature decline is the result of sulphate aerosols masking the warming effect of CO2 emissions?

Veerabhadran Ramanathan: After the 1970s, when the West was cleaning up pollution, there was a rise in temperatures. We stopped burning coal in cities etc, and coal puts out a lot of sulphates, and sulphates mask global warming. At the same time, in the tropics, China and India, they were growing fast and putting a lot more Black Carbon.

CR: So the sulphate component must have been reduced more than the Black Carbon component for the aerosol masking theory to hold? We now need empirical data to compare the effect of black and white aerosols during the post-war temperature slump?

VR: Exactly.

CR: Do we have that empirical data?

VR: No. The data we have is for 2002-2003. We don’t know what happened in the ’50s, ’60s and ’70s. The implication of this study is that we have to understand what is the relative change in the sulphur emissions versus the Black Carbon emissions – and we don’t know that.

CR: So what is the empirical evidence that, 50 years ago, white aerosols were masking GW due to CO2?

VR: It’s pretty flimsy. The main information we have […] is our understanding of the SO2 emissions by coal combustion, and oil. But we need to know not so much how much SO2 we put out, but how much was converted to sulphates, how much was removed [etc]

CR: So you don’t even know the life cycle of the SO2 and sulphates?

VR: No. All the information we have is from models… It could still be true [that white aerosols account for the post-war temperature slump]

CR: But it could not be true?

VR: Yes. The picture is complicated. But this paper is not saying it is wrong[…]

CR: So we now have a better idea of what is happening aerosol-wise in the present, but what was going on in the 1950s/’60s is still elusive?

VR: Yes, There’s a lot of research needs to be done on that – what happened in the ’50s and ’60s, and then why the rapid ramp up [from the ’70s]. I’m not saying our current understanding is wrong, just that it is a more complicated picture. I would say it’s uncertain.

We wouldn’t suggest the aerosol-masking theory is wrong either. What’s interesting is how a neat idea is sold as an established fact, how a working hypothesis has become a truth ‘well-known to all climate scientists’, how ’scientists are investigating’ becomes scientists ‘have explained’. Without the masking theory, the orthodoxy would have a serious problem. The research that shows that decade-long periods of static/declining temperatures are to be expected against the background of a warming trend (see the Spiked article above) makes no claims that such natural variation could account for the much longer post-war slump.

Meanwhile, it will be worth watching to see how the tactics of the climate orthodoxy change as – and if – the present slowdown in temperature rise continues. The slump has already robbed the orthodoxy of much of its potential for short-term alarmism about record temperatures, and the Met, for example, seems already to have ditched its yearly climate forecast in favour of a decadal one. And how long before serious efforts are made to explain the slump in causal terms – not to mention how quickly those investigations are deployed as proof that climate science has nailed it?

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