Despite a consensus among scientists on the use of ocean heat as a robust measure for anthropogenic global warming (AGW), air temperature continues to be employed as the icon of global climate projections.  In a recent AP article by Seth Borenstein, “Statisticians reject global cooling”, the Associated Press “gave temperature data to four independent statisticians and asked them to look for trends, without telling them what the numbers represented. The experts found no true temperature declines over time.”

A lot of mercury and red alcohol has been spilled over the last several years dissecting the reliability of near-surface temperature measurements.  The controversy has spawned high profile blogs dedicated to the scrutiny of surface station reliability and the analysis of climate statistics .  The exercise has proven to be fruitful in many cases, discovering systemic weaknesses in the network of surface stations, exposing sloppy calculations, and raising legitimate questions about the algorithms used to adjust raw data.  Though satellite air temperature measurements do not suffer from these limitations, our observations extend back only 30 years.

The use of air temperature as an index of global warmth has weak scientific support, except, perhaps, on a multi-decadal or century time-scale.  Climate scientists agree that 80% - 90% of the heat in earth’s climate system is stored in the oceans.  For any given area on the ocean’s surface, the upper 2.6 meters of water has the same heat capacity as the entire atmosphere above it!  Air temperature may not register accumulated ocean heat from year to year.  Since this heat is not always at the ocean’s surface, there may be long lags in air temperature response time.  But eventually, as the ocean heats or cools, air temperature is sure to follow.  Accordingly, the findings represented in Borenstein’s article are no surprise and do little to support or damage the case for AGW. 

Hype generated by scientists and activists over short-term changes in global air temperature (up or down) has diverted us from the real question:  Is heat accumulating in the world’s oceans?  Many climate scientists, including those at NASA’s Goddard Institute for Space Studies (GISS) and the British Met Office Hadley Centre for Climate Change, are being rather disingenuous in their use of air temperature.  They advocate ocean heat as a climate metric in research articles (including AR4 - the most recent IPCC report), but then use air temperature as a metric when discussing AGW with the public.  Presumably, from a marketing perspective, the man on the street cannot connect with “Joules of accumulated heat” absorbed by the ocean. 

So what does ocean heat tell us about the progress of global warming?  That’s the elephant in the living room that proponents of AGW aren’t talking about - at least not lately.  Writing in 2005, NASA scientists James Hansen, Josh Willis, Gavin Schmidt, et. al. suggested that their model projections of global warming had been verified by a solid decade of increasing ocean heat (1993 to 2003).  This was regarded as confirmation of the AGW hypothesis (see “Earth’s Energy Imbalance:  Confirmation and Implications”, Science, 3 June 2005, 1431-35). 

But by mid-2003 warming ceased rather abruptly and, by all appearances, not one Joule of energy has been added to the ocean for over 6 years.  According to some analysts there has been a slight cooling, even as CO2 levels continue to rise.  Advocates of AGW have dismissed this as natural variability.  But the implications are clear.  If the climate system is not accumulating heat, the hypothesis may be false.

See large image here.

The current trend also raises some pointed questions.  If climate change is now dominated by CO2 induced warming, what mechanism is responsible for the current cessation of warming?  The immediate cause is well known:  The periodic cooling and warming of ocean waters called the Pacific Decadal Oscillation (PDO).  But the underlying causes of the PDO itself are not well understood, which is also true for much of the variability in our climate system.

If we cannot explain the causes behind natural variability, then how can we project future climate trends?  Moreover, how can we be sure that the prior warming trend was anthropogenic rather than natural?  After all, we cannot eliminate from consideration causes we do not understand.  Borenstein’s article proceeds on the assumption that if there is warming, it must be anthropogenic, and it must be from CO2.  The question of attribution - the most difficult scientific question of all - is never raised. 

At the very least, the flattening of ocean heat over the last 6 years should raise cautionary flags and provoke a re-examination of climate model projections.  If CO2 induced warming is so easily overwhelmed by natural variability, then perhaps the threat of “runaway warming” and climate “tipping points” has been overstated.  Despite the sophistication of our efforts, perhaps our ignorance exceeds our knowledge.

Unfortunately, climate scientists who continue to hide behind the metric of air temperature are dodging the hard questions.  Repeated efforts to confront them on the issue of ocean heat have met with silence (see Roger Pielke’s article here).  Now that heat accumulation has stopped (and maybe even reversed), the tables have turned.  The same criterion used to confirm Anthropogenic Global Warming, is now challenging its legitimacy. See full post with citations here.

Bill DiPuccio was a weather forecaster and instructor for the U.S. Navy, and a Meteorological/Radiosonde Technician for the National Weather Service.  More recently, he served as head of the science department for St. Nicholas Orthodox School in Akron, Ohio (closed in 2006).  He continues to write science curriculum, publish articles, and conduct science camps.