1. The Diurnal Temperature Range and its Recent Evolution
Brian Olsen
April 20, 2006

2. Outline Introduction to DTR Local Examples Global Trends
What affects DTR?
Conclusions

3. The Global Warming Signal
Multi-decadal “pause” in warming
IPCC, 2001

4. Diurnal Temperature Range (DTR)
DTR = High - Low
High Temperature = 81F
Low Temperature = 58 F
DTR = 81 F – 58 F = 23 F
Lowest in winter
Highest in summer
SLC WFO

5. KSLC Trends But why? What about a nearby rural location? Warming?
Definite Warming!
E. Crossman
But why?
What about a nearby rural location?

6. KENV Monthly Mean of Daily Tmax, Tmin, and DTR (1913-2004)
General loss of warm colors in summer
Missing data
General gain of cool colors in winter
B. Olsen

7. KENV Trends But where did the trend go?
Tmax actually decreases
Tmin increases
DTR decreases
But where did
the trend go?
Obviously, this is a complicated problem
Pause in warming
B. Olsen

8. Global Trends (1950 - 2004) Strong Warming Steady Strong Warming
Decreasing
Steady
Vose et al. 2005
Vose et al. 2005

9. 1950 – 2004 1979 - 2004 < ≈ Vose et al. 2005 Greatest Warming
1950 –
< ≈
Greatest Warming
Greatest Warming
Vose et al. 2005

10. Global Trends (1979 – 2004) Trendless Vose et al. 2005

11. Why? What Affects DTR? Other considerations
Urban Heat Island (increase minimums) – local effect
Irrigation & Desertification not globally significant – local effect
Climate variables
Cloud coverage and altitude explain ~40% of variance
All vars ~55% of variance
Other considerations
Jet Contrails (Travis et al. 2004)
Tropospheric aerosol
GHG emissions
Correlation Coefficient
Karl et al. 1993

12. Conclusions The planet is warming The planet is getting less cool
Historically, minimum temps increased more than maximum temps => decrease in DTR
Winter / Spring warmed the most
Rate of warming has increased since 1980
Recently, minimum temps and maximum temps rise in step => no trend in DTR
Winter continues to become more mild
Signal most apparent in Northern Hemisphere
Cloud cover is significant

13. (In)Conclusions DTR trend is difficult to measure
difference between two large quantities
Noisy / lots of temporal variability
Wide regional variation
Global generalizations may be a poor measure
Local effects may overpower global trend
Model / Observation discrepancy

14. Thanks!