Climate Letter #1324

An important new study has key information about the historical masking effect of air pollution.  The effect, which is the result of burning fossil fuels, has blocked enough sunlight to reduce the warming caused by greenhouse gas emissions by a significant amount.  The actual amount of blocking over time has not been at all uniform with respect to either global regions or time periods, depending on when and where fossil fuel burning is being increased and when and where the most efforts are being made to clean up its pollution effects.  All of that is revealed in the study with an assortment of charts.  A key point is that once CO2 is added to the atmosphere it stays there for centuries while pollution must constantly be replenished on a practically daily basis.  Here is the main story:

–Access to the full study:  https://www.pnas.org/content/early/2018/12/12/1813951115

–Here is a separate link to just the figures used in the study.  The one at the top provides what I believe is the best information you can get from the study, for both the main details and also an overall explanation of what lies behind the overall global warming trend that we see all the time in various charts.  There just wasn’t much net warming before about 1975 because it was held back by huge amounts of pollution in the early developing countries like Europe and the US.  After that got cleaned up the temperature uptrend we see could get underway, but with a new set of effects caused mainly by the Chinese development trend that started around that same time.  Air pollution is destined to finally disappear if fossil fuel burning ever ends, as it must.

–One more comment:  The study does not provide any help with interpreting the temperature changes that come about because of all the net forcing effects.  Instead, everything is expressed in terms of watts per square meter, an immediate type of effect that is statistically applied, on average, to the entire surface of the globe, usually shown as a gain or loss over time.  Temperature changes will always follow, but only over extended periods of time.  As a rule of thumb, most scientists accept the idea that every net change of one watt per square meter will eventually lead to a change of 0.75C in the global temperature average once everything is in equilibrium.  The study calculations show that an end to the current air pollution caused by burning fossil fuels would add almost one watt of solar radiation to the amount that now reaches the surface.

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A new report stresses the need to reduce greenhouse gas emissions from agriculture.  This sector is the world’s largest source of non-CO2 emissions, in the form of methane and nitrous oxide.  These emissions represent 10-12% of the total power of all greenhouse gas emissions caused by human activity, making them an important part of any mitigation program.  There are some practical ways discussed for how this can be accomplished, with varying degrees of difficulty.

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A report on the cement industry and its massive CO2 emissions (BBC News).  This story is full of information about the growth and overall importance of a vital industry that produces 8% of the total CO2 emissions due to human activity, that somehow must be abridged.  The larger share of these emissions come from the processing of raw material, the rest from the required energy that is involved.  “If the sector has any hope of meeting its commitments to the 2015 Paris Agreement on climate change, it will need to look at overhauling the cement-making process itself, not only reducing the use of fossil fuels.”  Possible ways of meeting that goal are discussed.

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