John Ward: Get to work on global warming
Published: Monday, June 10, 2013 at 4:23 p.m.
Last Modified: Monday, June 10, 2013 at 4:23 p.m.
The flattening of the global temperature rise over the last 15 years has led some scientists to conclude that global warming may pose less of a threat than expected. But this conclusion ignores the undeniable fact that more heat is entering the atmosphere than leaving, and at an increasing rate.
Inability to account for this discrepancy led Kevin Trenberth, distinguished senior scientist at the National Center for Atmospheric Research, to exclaim in an widely-reported email, "The fact is that we can’t account for the lack of warming at the moment and it is a travesty that we can’t." Well, now we can.
A recent study in Geophysical Research Letters by Balmaseda, Trenberth, and Källén (2013) accounts for the discrepancy: 90 percent of all global warming is absorbed by the oceans, which have been rapidly heating up. Much of the extra heat, missing from the earth's surface and atmosphere, has been found in ocean depths below 700 meters, which account for about 30 percent of all global warming, and a lesser amount of heat increase occurs above that level.
Using data from the European Centre for Medium-Range Weather Forecasts’ Ocean Reanalysis System 4, Balmaseda et al. found a steep increase in lower ocean heat after 2000, the period during which surface temperatures have increased less than expected. The heat gain in the lower ocean is expected at some point to move to the upper ocean and the atmosphere, where it will rapidly increase temperatures. Another recent study, Guemas et al. (2013), also concludes that much of the recent warming has gone into the ocean below the surface levels.
These conclusions confirm those of earlier studies, such as Levitius et al. (2012), Nuticelli et al. (2012), and Meehl et al. (2011). Meehl identified "hiatus periods" of a decade or more during which increased heat went into ocean depths below 750 meters and levels from 300 to 750, but a decreased amount of heat went into levels above 300 meters followed by periods of surface temperature increases where the excess heat left the lower ocean levels. He concluded that these alternations were caused by natural variability, which occurred even during periods of long term warming.
The shifts between El Niño and La Niña years is another such natural variable that does not affect the long-term global warming the planet is experiencing. La Niña events may have a cooling effect by shifting warmed water to deeper ocean levels and the reverse for El Niños. The relative absence of strong El Niño weather in the last decade has contributed to slow warming temporarily.
Another cause of the leveling of recent global atmospheric temperatures is the per year increase since 2000 by 4 to 10 percent in the optical depth of the stratospheric aerosol layer, largely composed of sulfur dioxide, which is known to reflect heat and reduce warming of the lower atmosphere. A recent study, Neely et al., attributes this increase largely to "the moderate volcanic explosive injections of SO2 observed from 2000 to 2010." But whatever the cause, the increase and its cooling effect are not in dispute.
Two important, newly reported studies have found that we have underestimated the ability of the planet to heat up quickly: One, Eagle et al., (2013), using a new, more accurate procedure, found that temperatures in central China are presently 10 to 14 degrees hotter than temperatures during the last ice age 20,000 years ago, two to four times the increase previously believed. The lead author said "We were surprised at how poorly most climate models predicted temperature change in central China and also surprised at how sensitive this region has been to changes in climate forcing.”
The other study, Brigham-Grette, Melles, and Koeberl (2013), of the longest uninterrupted sediment core ever collected on Arctic land under Lake El´gygytgyn in Russia, found that temperatures at a time several million years ago rose to levels significantly higher than expected. The lead scientist said, "“One of our major findings is that the Arctic was very warm in the Pliocene [~ 5.3 to 2.6 million years ago] when others have suggested atmospheric CO2 was very much like levels we see today. This could tell us where we are going in the near future. In other words, the Earth system response to small changes in carbon dioxide is bigger than suggested by earlier models.”
Both discoveries indicate that climate sensitivity is stronger than currently believed. This evidence further weakens the position of climate change deniers, for whom climate sensitivity must be lower than currently believed, not higher, in order for them to credibly claim that the huge increase in CO2 will have little effect on temperature.
In view of the accumulating evidence that global warming will continue to increase and that addressing the problem will become more expensive and less effective the longer we wait to make it our highest priority, in light of the severe threat it poses to our climate, economy, heath, freedom and way of life, it is urgent that we demand that Congress and the president get to work on lowering greenhouse gas emissions as rapidly as possible and cooperate with other nations to do the same. A carbon tax, with the proceeds distributed equally to all citizens, would be a good start.
The harmful effect already reported of ocean acidification on coral, oysters, clams, and mussels, the unprecedented destruction by mountain pine beetles of vast expanses of trees in the Northwest of the U.S. and Canada, formerly protected by colder temperatures, the swiftly spreading disease destroying the African cassava crop, transmitted by flies that are rapidly increasing with rising temperatures, are a few of the proliferating hints of the much greater damage that unrestrained global warming will cause for our children and grandchildren.
John L. Ward lives in Gainesville.