Tuesday, March 19, 2013

Has Global warming stopped or paused to catch its breath?



Continuing reports of a “global standstill” in average surface temperatures compare the flat temperature trend since 1998 with the continuing linear increase in atmospheric CO2 concentration, reducing the correlation between them and arguing that increasing CO2 does not cause increasing global average surface temperature. (http://www.nasa.gov/pdf/719139main_2012_GISTEMP_summary.pdf)

It has also been pointed out, sometimes in the same articles, that paleoclimate proxy records indicate that increasing global average surface temperature precedes increases in atmospheric CO2 concentration by 200 to 800 years, indicating, therefore, that increased temperature causes increased CO2 concentration, not the other way round. Oceanic temperature lag is proposed as the mechanism for this lag in ocean CO2 absorption/emission.

If both the above are true, that would mean that the observed rise in CO2 concentration is caused by global average temperature increases that occurred 200 to 800 years ago, not by the presently observed temperature increase. That would place the temperature increase that caused the present CO2 rise from ~1200 to ~1800 AD.

This would mean, then,  that the present increase in atmospheric CO2 concentration is the result of the continuing rebound from Little Ice Age temperatures at the end of the 16th Century, as global average surface temperature returns to the long-term normal average surface temperature of 15 degrees C. As average temperature approaches the long-term “normal,” we would expect a flattening of the rate of increase until a plateau is reached, all other influences remaining equal.

Natural Climate Variation
Holocene temperature fluctuations are the result of combinations of natural insolation cycles, overlain by much shorter cycles of multi-decadal oscillations and periods of varying volcanic activity. (See Akasofu, S., 2010, On the recovery from the Little Ice Age, Natural Science, Vol.2, No.11, 1211-1224)

This does not mean that anthropogenic CO2 does not affect climate variation, but it cannot be supported as the sole cause of observed climate variation in the historical record. Until we understand and quantify natural climate variation and its proximate causes, we cannot fully quantify the effects of anthropogenic CO2. However, if the above proposition is true, the contribution of anthropogenic CO2 to the atmosphere can have only a minimal effect on global average surface temperature, in the range of .5C per century or less. (Akasofu 2010)

This understanding of the causes of atmospheric CO2 increase undercuts the IPCC policy position on anthropogenic global warming, as well as the political and economic arguments for lowering anthropogenic CO2 emissions as a means of influencing observed climate variation. Under this scenario, reduction of fossil fuel use and the revival of a nuclear energy program will not reduce observed increases in global average surface temperature to any significant degree.

The Decline of Environmentalism
This growing realization of the nature of observed climate variation is already finding expression in popular press and is changing the rhetoric of the global warming debate. Unfortunately, the contentious debate between “deniers” and “alarmists” has poisoned the well of environmental activism and popular appreciation and understanding of science in general. It will be an uphill struggle to reestablish a public appreciation for the necessity of continuing work in pollution reduction, habitat preservation, energy conservation and renewable energy production. 

Ironically, it may well turn out that the recent unwarranted concentration on “global warming” has set back the cause and the course of working toward resilient societies that are better able to accommodate to a naturally variable climate.