The Diurnal Temperature The Diurnal Temperature Range and its Recent Range and its Recent

EvolutionEvolution

Brian OlsenBrian Olsen

April 20, 2006April 20, 2006

OutlineOutline

• Introduction to DTRIntroduction to DTR

• Local ExamplesLocal Examples

• Global TrendsGlobal Trends

• What affects DTR?What affects DTR?

• ConclusionsConclusions

The The GlobalGlobal Warming Signal Warming Signal

IPCC, 2001

Multi-decadal “pause” in warming

Diurnal Diurnal TemperatureTemperature Range (DTR) Range (DTR)

• DTR = High - LowDTR = High - Low

• High Temperature = 81FHigh Temperature = 81F

• Low Temperature = 58 FLow Temperature = 58 F

• DTR = DTR = 81 F81 F – – 58 F58 F = = 23 F23 F

SLC WFO

Highest in summer

Lowest in winter

KSLCKSLC Trends Trends

Warming?

Definite Warming!

E. Crossman

• But why?But why?• What about a nearby rural location?What about a nearby rural location?

KENV KENV MonthlyMonthly Mean of Daily Mean of Daily TTmaxmax, T, Tminmin, and DTR (1913-2004), and DTR (1913-2004)

B. OlsenB. Olsen

Missing data

General loss of warm colors in

summer

General gain of cool colors in

winter

KENVKENV Trends Trends• Tmax actually decreases• Tmin increases• DTR decreases

But where didBut where did the trend go?the trend go?

• Obviously, this isObviously, this is a complicated a complicated problem problem

Pause in warming

B. OlsenB. Olsen

Global TrendsGlobal Trends(1950 - 2004)(1950 - 2004)

Vose et al. 2005Vose et al. 2005

Vose et al. 2005Vose et al. 2005

Steady

Warming

StrongWarming

StrongWarming

SteadyDecreasing

1950 – 2004 1979 - 20041950 – 2004 1979 - 2004

Vose et al. 2005

GreatestWarming

GreatestWarming

< ≈

Global TrendsGlobal Trends(1979 – 2004)(1979 – 2004)

Trendless

Vose et al. 20052005

Vose et al. 2005Vose et al. 2005

WhyWhy? What Affects DTR?? What Affects DTR?

• Urban Heat Island (increase minimums) – local effectUrban Heat Island (increase minimums) – local effect

• Irrigation & Desertification not globally significant – local effectIrrigation & Desertification not globally significant – local effect

• Climate variablesClimate variables

– Cloud coverage and altitudeCloud coverage and altitudeexplain ~40% of varianceexplain ~40% of variance

– All vars ~55% of varianceAll vars ~55% of variance

• Other considerationsOther considerations– Jet Contrails (Travis et al. 2004)Jet Contrails (Travis et al. 2004)

– Tropospheric aerosolTropospheric aerosol

– GHG emissionsGHG emissions

RH WS CIG TRAD dTMP SKY SNOW-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8Simple

Partial

Cor

rela

tion

Coe

ffici

ent

Karl et al. 1993Karl et al. 1993

ConclusionsConclusions

• The planet is warmingThe planet is warming• The planet is getting less coolThe planet is getting less cool• Historically, minimum temps increased more than maximum temps Historically, minimum temps increased more than maximum temps

=> decrease in DTR=> decrease in DTR• Winter / Spring warmed the mostWinter / Spring warmed the most• Rate of warming has increased since 1980Rate of warming has increased since 1980• Recently, minimum temps and maximum temps rise in step => no Recently, minimum temps and maximum temps rise in step => no

trend in DTRtrend in DTR• Winter continues to become more mildWinter continues to become more mild• Signal most apparent in Northern HemisphereSignal most apparent in Northern Hemisphere• Cloud cover is significantCloud cover is significant

(In)Conclusions(In)Conclusions

• DTR trend is difficult to measureDTR trend is difficult to measure– difference between two large quantitiesdifference between two large quantities– Noisy / lots of temporal variabilityNoisy / lots of temporal variability

• Wide regional variationWide regional variation– Global generalizations may be a poor Global generalizations may be a poor

measuremeasure– Local effects may overpower global trendLocal effects may overpower global trend

• Model / Observation discrepancyModel / Observation discrepancy

ThanksThanks!!