3Qs: Hot, hot heat

June 28, 2012 by Jason Kornwitz

A record-​​breaking heat wave hit the East Coast last week, fol­lowed by a spate of rain and thun­der­storms. Northeastern University news office asked Auroop Gan­guly, an asso­ciate pro­fessor of civil and envi­ron­mental engi­neering whose exper­tise lies in under­standing cli­mate change and extreme weather, to explain the rela­tion­ship between heat waves and global warming.

How do you define and track a heat wave?

Like many other extreme weather phe­nomena, there is no single way to define or track heat waves, but common def­i­n­i­tions take into account their poten­tial impacts. The heat index, for example, is an aggre­gate mea­sure that com­bines tem­per­a­ture and humidity — two pri­mary weather fac­tors that deter­mine human per­cep­tion of heat. On the other hand, human mor­tality, in the dev­as­tating heat waves of Chicago or Paris, for example, is often caused not just by high day­time tem­per­a­tures but by con­sec­u­tive night­time tem­per­a­tures exceeding cer­tain thresh­olds. One other mea­sure for heat waves is cooling degree days, which attempts to relate tem­per­a­tures to energy demand for air conditioning.

For agri­cul­ture and food secu­rity, heat waves and tem­per­a­ture extremes may be defined through spe­cific thresh­olds beyond which cer­tain crops cannot sur­vive. Occa­sion­ally while studying cli­mate vari­ability or change, we track tem­per­a­tures that set new records, which would in turn vary depending on the region and the season. One sta­tis­tical method to define and track extremes is through the rig­orous “extreme value theory,” which lead to met­rics such as 100-​​year return periods. This is the prob­a­bility that a given tem­per­a­ture will be exceeded once every 100 years on the average.

On the whole, the def­i­n­i­tion and tracking of heat waves is very much depen­dent on the end use. Mete­o­rol­o­gists often prefer relying on the heat index or record tem­per­a­tures for given regions and sea­sons. Energy com­pa­nies and plan­ners tend to look at cooling degree days. Agri­cul­tural plan­ners may be inter­ested in the pos­si­bility of tem­per­a­tures exceeding cer­tain thresh­olds. Cli­mate sci­en­tists inter­ested in adap­ta­tion to cli­mate change or in the phys­ical sci­ences have devel­oped an array of met­rics based on the con­se­quences of heat waves or on their link­ages to atmos­pheric physics or a combination.

Do global warming and higher temperatures go hand in hand?

In gen­eral, it is very unlikely if not impos­sible that any one heat wave, cold snap, dry spell or inci­dence of heavy rain­fall could be related to longer-​​term nat­ural cli­mate vari­ability or anthro­pogenic, or man-​​made, global warming. Cer­tainly, a heat wave at this time of the year in the North­east is not uncommon and should be viewed as weather phe­nomena rather than cli­mate phe­nomena. Weather is what’s hap­pening at any given moment and cli­mate is average weather over a period of time.

On the other hand, global warming is pro­jected to increase the occur­rence of heat waves, implying that longer lasting, more fre­quent and more intense heat waves are con­sis­tent with what one would expect as the Earth con­tinues to get warmer. How­ever, large uncer­tain­ties remain when assigning causality to spe­cific instances of regional heat waves or other weather events. In one of my 2009 papers pub­lished in the journal Pro­ceed­ings of the National Academy of Sci­ences, for example, we found that while are likely to grow even worse than pre­vi­ously thought, the remaining uncer­tain­ties and geo­graph­ical vari­ability are also more than pre­vi­ously believed.

What causes climate variability, such as changes in precipitation patterns, and what impact may it have on the environment?

Cli­mate vari­ability may be caused by nat­ural cycles ranging across dif­ferent time scales, such as the inter-​​annual El Nino to the 60– to 70-​​year Atlantic Mul­ti­decadal Oscil­la­tion. The growing tem­per­a­ture trends owing to anthro­pogenic , which is super­posed over and above nat­ural vari­ability, has been noticed or is pro­jected to occur at multi-​​decadal to cen­tury scales.

At the other end of the time scale are very long-​​term changes, including changes in mon­soon rain­fall pat­terns. These pat­terns have been sug­gested as a likely cause for the decay of a 4000-​​year-​​old long-​​lost urban civ­i­liza­tion in the Indus valley. These dif­ferent time scales — from day-​​to-​​day weather and nat­ural cli­mate oscil­la­tions of sev­eral decades to century-​​scale warming trends and longer-​​term nat­ural vari­ability in the Earth’s cli­mate system — are impor­tant to under­stand and acknowl­edge when attempting to under­stand cli­mate change.

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4.5 / 5 (8) Jun 28, 2012
Temperatures are only expected to rise. As Al-Gore show so vividly in his movie (and book), "An Inconvenient Truth", we are just at the very begins of the front side of an exponential rise. It's only June and there are many more 100F degree weeks in-store for the mid-west. Given drought conditions too, the USA is going to look like Russia did last year.
4.4 / 5 (7) Jun 28, 2012
How can the U.S. be experiencing so many record breaking temperatures when the denialists continue to tell us that the world is cooling?

It must be a conspiracy.

1.6 / 5 (7) Jun 29, 2012
"The 1936 North American heat wave was the most severe heat wave in the modern history of North America. "
"The heat wave started in late June, when temperatures across the US exceeded 100 °F (38 °C). The Midwest experienced some of the highest June temperatures on record. Drought conditions worsened. In the Northeast, temperatures climbed to the mid 90s °F (around 35 °C)."
"July was the peak month, in which temperatures reached all-time record levelsmany of which still stand as of 2010. In Steele, North Dakota, temperatures reached 121 °F (49 °C), which remains North Dakota's record. "
"Detroit's killer heat wave of 1936"
1.5 / 5 (8) Jun 29, 2012
Too many coincidences, 1936 to 2012?
Socialist govt in the USA.
Poor economies around the world.
Threats of war by socialist tyrannies.
High summer temperatures.
That's a 78 year spread or seven 11 year solar cycles.
1 / 5 (6) Jun 29, 2012
"In July 1954 a heat wave with 22 days of temperatures over 100 degrees covered significant parts of 11 states, including Illinois. The highest recorded temperature in Illinois was 117 degrees on July 14 in East St. Louis, which still stands as the state record."
Sunspot numbers declining in 1954:
1 / 5 (6) Jun 29, 2012
(Royal Netherlands Meteorological Institute, De Bilt)
(Manuscript received 5 August 1949)"

"We arrive at the following conclzbsion : A negative correlation
exists between solar activity and heat waves with a phuse diflerence
of 21 days, or - 6 days."

4.4 / 5 (7) Jun 30, 2012
In 1936 over 5000 deaths are attributed to the excess heat. The crops of several States were wiped out by the drought conditions as well as excessive heat. This year, records are being broken for the hottest June ever recorded exceeding 1936 in some locations of the central and eastern US. July and August are looking to be the same as there is not much change the general climate patterns. It looks like AGW is the only explanation that fits the observations.

And it all fits exactly to what Al-Gore (et al) predicted.

1.6 / 5 (7) Jun 30, 2012
exceeding 1936 in some locations

So, why was 1936 just as hot?
1.6 / 5 (7) Jun 30, 2012
exceeding 1936 in some locations

So, why was 1936 just as hot?
1.6 / 5 (7) Jun 30, 2012
"Thunderstorms can generally form and develop in any geographic location, perhaps most frequently within areas located at mid-latitude when warm moist air collides with cooler air."

The west coast has been very cold and many cold records were set in Florida.


Cold records don't get mentioned.

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