"There’s one constant about D.C. summer, and that’s a lot of hot days. Right? Not always.
While 2014′s average temperature for meteorological summer (Jun-Aug) is running fairly close to “normal,” as defined by the 1981-2010 climate period, it’s undoubtedly been among the more pleasant in recent memory when it comes to daytime heat.
With only 16 days featuring high temperatures at or above 90 degrees this year, we’re a week behind last year’s tally year-to-date, and 32 days (more than a month!) behind the pace of the scorching 2010-2012 summers. The average year-to-date total is around 29.
On the low end, 2004 sets the recent low mark when it comes to cumulative 90 degree days, at only 11. It reached that number prior to mid-August, and stayed there for the entire warm season. 2009 was more or less on par with this year at this point, having only racked up 15 by mid-August. It finished with 22.
Over the entire D.C. history going back to the 1880s, D.C. seeing so few 90 degree days through mid-August is about a one in five chance. However, two thirds of the years in which this happened occurred before the switch of observation location from downtown to National Airport in the mid-1940s.
There have actually been 17 years dating back to 1872 that finished with only 16 days at or above 90 degrees during the extended summer months, many were fewer. Three of these years with missing 90s occurred since 2000 (2001 had 16, 2000 had 12, and 2004 had 11). 2004′s tally is the record holder for lowest in a year at National.
Going way back, in 1886 and 1905 we only managed 7 days in the 90s or higher. Those are low marks that are almost undoubtedly safe for eternity.***
Finally, during the 10-year period prior to this one, D.C. recorded about 80% of its 90 degree or warmer days by August 15. It’s roughly the same for the longer climatological average. That would put us on pace for about 20.
Where do you think we’ll finish this year?"
"Ian Livingston is a forecaster/photographer and information lead for the Capital Weather Gang. By day, Ian is a defense and national security researcher at a D.C. think tank." Images from Washington Post, via Drudge
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***Comment: "Eternity" has already produced at least 5 ice ages including the one in which we live today. Therefore it's not "safe" to predict US temperature records of the past 150 years will stand forever as Mr. Livingston does:
"At least five major ice ages have occurred throughout Earth’s history: the earliest was over 2 billion years ago, and the most recent one began approximately 3 million years ago and continues today (yes, we live in an ice age!)."...11,000 years ago global temps. rose 20 degrees F in just a few years. "In a relative sense, we are in a time of unusually stable temperatures today." Utah gov.
Sept. 2010, "Ice Ages--What are they and what causes them?" Utah Geological Survey, geology.Utah.gov, by Sandy Eldredge and Bob Biek
"What is an ice age? An ice age is a long interval of time (millions to tens of millions of years) when global temperatures are relatively cold and large areas of the Earth are covered by continental ice sheets and alpine glaciers. Within an ice age are multiple shorter-term periods of warmer temperatures when glaciers retreat (called interglacials or interglacial cycles) and colder temperatures when glaciers advance (called glacials or glacial cycles).
At least five major ice ages have occurred throughout Earth’s history: the earliest was over 2 billion years ago, and the most recent one began approximately 3 million years ago and continues today (yes, we live in an ice age!).
Currently, we are in a warm interglacial that began about 11,000 years ago. The last period of glaciation, which is often informally called the “Ice Age,” peaked about 20,000 years ago. At that time, the world was on average probably about 10°F (5°C) colder than today, and locally as much as 40°F (22°C) colder.
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| 2002 chart, Utah gov. |
What causes an ice age and glacial-interglacial cycles? Many factors contribute to climate variations, including changes in ocean and atmosphere circulation patterns, varying concentrations of atmospheric carbon dioxide, and even volcanic eruptions. The following discusses key factors in (1) initiating ice ages and (2) the timing of glacial-interglacial cycles.
One significant trigger in initiating ice ages is the changing positions of Earth's ever-moving continents, which affect ocean and atmospheric circulation patterns. When plate-tectonic movement causes continents to be arranged such that warm water flow from the equator to the poles is blocked or reduced, ice sheets may arise and set another ice age in motion.
Today’s ice age most likely began when the land bridge between North and South America (Isthmus of Panama) formed and ended the exchange of tropical water between the Atlantic and Pacific Oceans, significantly altering ocean currents.
Glacials and interglacials occur in fairly regular repeated cycles. The timing is governed to a large degree by predictable cyclic changes in Earth’s orbit, which affect the amount of sunlight reaching different parts of Earth’s surface. The three orbital variations are: (1) changes in Earth’s orbit around the Sun (eccentricity), (2) shifts in the tilt of Earth’s axis (obliquity), and (3) the wobbling motion of Earth’s axis (precession).
How do we know about past ice ages? Scientists have reconstructed past ice ages by piecing together information derived from studying ice cores, deep sea sediments, fossils, and landforms. Ice and sediment cores reveal an impressive detailed history of global climate. Cores are collected by driving long hollow tubes as much as 2 miles deep into glacial ice or ocean floor sediments. Ice cores provide annual and even seasonal climate records for up to hundreds of thousands of years, complementing the millions of years of climate records in ocean sediment cores.
Within just the past couple of decades, ice cores recovered from Earth’s two existing ice sheets, Greenland and Antarctica, have revealed the most detailed climate records yet.
Do ice ages come and go slowly or rapidly? Records show that ice ages typically develop slowly, whereas they end more abruptly. Glacials and interglacials within an ice age display this same trend.
On a shorter time scale, global temperatures fluctuate often and rapidly. Various records reveal numerous large, widespread, abrupt climate changes over the past 100,000 years. One of the more recent intriguing findings is the remarkable speed of these changes. Within the incredibly short time span (by geologic standards) of only a few decades or even a few years, global temperatures have fluctuated by as much as 15°F (8°C) or more.
For example, as Earth was emerging out of the last glacial cycle, the warming trend was interrupted 12,800 years ago when temperatures dropped dramatically in only several decades. A mere 1,300 years later, temperatures locally spiked as much as 20°F (11°C) within just several years. Sudden changes like this occurred at least 24 times during the past 100,000 years. In a relative sense, we are in a time of unusually stable temperatures today—how long will it last?"
Chart above: "Simplified chart showing when the five major ice ages occurred in the past 2.4 billion years of Earth’s history. Modified from several sources including Dynamical Paleoclimatology: Generalized Theory of Global Climate Change, 2002, by Barry Saltzman." From Utah.gov
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Added: In 2012 $1 billion a day was invested in the notion of imaginary human caused global warming.
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