Sunday, May 06, 2007

Storm guru: Oceans, not CO2, cause warming

I ran across this interesting Associated Press article entitled "Storm guru: Oceans, not CO2, cause warming" which tells us that the top hurricane forecaster in the world believes that global warming has resulted from multi-decade cyclical changes in ocean currents and not man-made carbon dioxide.

Dr. William Gray, is Professor of Atmospheric Science and  Head of the Tropical Meteorology Project at Colorado State University in Fort Collins, Colorado. Everybody who cares about hurricanes in the Caribbean and the eastern seaboard of the U.S. waits patiently every year for his hurricane forecast, including insurance companies, Wall Street, and commodities traders. The guy really knows his stuff.

Still, even though this is the guy who has the best expertise at modeling the oceans and atmosphere with regard to tropical storms, somehow the proponents of global warming and climate change think they know better.

Check out his Tropical Metrology Project for background. And see his 2007 Hurricane Forecast, which also includes a section entitled "Is Global Warming Responsible for the Large Upswing in 2004-2005 U.S. Hurricane Landfalls?" which essentially answers "No." Some specifics:

The Atlantic has seen a very large increase in major hurricanes during the 12-year period of 1995-2006 (average 3.9 per year) in comparison to the prior 25-year period of 1970-1994 (average 1.5 per year).  This large increase in Atlantic major hurricanes is primarily a result of the multi-decadal increase in the Atlantic Ocean thermohaline circulation (THC) that is not directly related to global temperature increase or to human-induced greenhouse gas increases.   Changes in ocean salinity are believed to be the driving mechanism.  These multi-decadal changes have also been termed the Atlantic Multidecadal Oscillation (AMO). 

There have been similar past periods (1940s-1950s) when the Atlantic was just as active as in recent years.  For instance, when we compare Atlantic basin hurricane numbers over the 15-year period (1990-2004) with an earlier 15-year period (1950-1964), we see no difference in hurricane frequency or intensity even though the global surface temperatures were cooler and there was a general global cooling during 1950-1964 as compared with global warming during 1990-2004.

Although global surface temperatures have increased over the last century and over the last 30 years, there is no reliable data available to indicate increased hurricane frequency or intensity in any of the globe's seven tropical cyclone basins, except for the Atlantic over the past twelve years.  Meteorologists who study tropical cyclones have no valid physical theory as to why hurricane frequency or intensity would necessarily be altered significantly by small amounts (< ±0.5oC) of global mean temperature change.

In a global warming or global cooling world, the atmosphere's upper air temperatures will warm or cool in unison with the sea surface temperatures.  Vertical lapse-rates will not be significantly altered.  We have no plausible physical reasons for believing that Atlantic hurricane frequency or intensity will change significantly if global ocean temperatures continue to rise.  For instance, in the quarter-century period from 1945-1969 when the globe was undergoing a weak cooling trend, the Atlantic basin experienced 80 major (Cat 3-4-5) hurricanes and 201 major hurricane days.  By contrast, in a similar 25-year period of 1970-1994 when the globe was undergoing a general warming trend, there were only 38 major hurricanes (48% as many) and 63 major hurricane days (31% as many) in the Atlantic basin.  Atlantic sea-surface temperatures and hurricane activity do not necessarily follow global mean temperature trends.

The most reliable long-period hurricane records we have are the measurements of US landfalling tropical cyclones since 1900 (Table 7).  Although global mean ocean and Atlantic surface temperatures have increased by about 0.4oC between these two 50-year periods (1900-1949 compared with 1956-2005), the frequency of US landfall numbers actually shows a slight downward trend for the later period.  If we chose to make a similar comparison between US landfall from the earlier 30-year period of 1900-1929 when global mean surface temperatures were estimated to be about 0.5oC colder than they were during the 30-year period from 1976-2005, we find exactly the same US hurricane landfall numbers (54 to 54) and major hurricane landfall numbers (21 to 21).

We should not read too much into the two hurricane seasons of 2004-2005.  The activity of these two years was unusual but well within natural bounds of hurricane variation.  In addition, following the two very active seasons of 2004 and 2005, 2006 had slightly below-average activity, and no hurricanes made landfall in the United States.

Between 1966 and 2003, US major hurricane landfall numbers were below the long-term average.  Of the 79 major hurricanes which formed in the Atlantic basin from 1966-2003, only 19 (24 percent) of them made US landfall.  During the two seasons of 2004-2005, seven of 13 (54 percent) came ashore.  None of the two major hurricanes that formed in 2006 made US landfall.  This is how nature sometimes works.

What made the 2004-2005 seasons so unusually destructive was not the high frequency of major hurricanes but the high percentage of major hurricanes which were steered over the US coastline.  The major US hurricane landfall events of 2004-2005 were primarily a result of the favorable, upper-air steering currents present during these two years.

The article reports that:

Gray complained that politics and research into global warming have created "almost an industry" that has unfairly frightened the public and overwhelmed dissenting voices.

He said research arguing that humans are causing global warming is "mush" based on unreliable computer models that cannot possibly take into account the hundreds of factors that influence the weather.

Gray said ocean circulation patterns are behind a decades-long warming cycle. He has argued previously that the strength of these patterns can affect how much cold water rises to the surface, which in turn affects how warm or cold the atmosphere is.

He also disputed assertions that greenhouse gases could raise global temperatures as much as some scientists predict.

"There's no way that doubling CO2 is going to cause that amount of warming," he said.

In response to Gray's carefully reasoned arguments and expertise, global warming and climate change proponent Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research in Boulder, Colorado replied that:

... natural changes in the environment cannot account for the magnitude of global warming in the past four decades.

"Since about 1970, the global temperature change is outside of the range of natural variability," he said in an interview.

He also challenged Gray's assertion that ocean currents have more effect on temperatures than carbon dioxide and other greenhouse gases.

"Global warming is pervasive. It has an influence on everything," Trenberth said. "It has an influence on ocean currents, it has an influence on hurricanes, it has an influence on rainfall."

Trenberth said computer climate models are the best quantitative tools available for predicting climate change. "They have been getting better over time," he said.

Trenberth's response doesn't seem very persuasive. I have no doubt that "computer climate models ... have been getting better over time", but it does appear that they simply aren't "there" yet. If they are unable to beat Gray's annual forecasts, why do so many people believe they can model global climate many decades into the future?

-- Jack Krupansky


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