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The Diurnal Temperature Range and its Recent Evolution

The Diurnal Temperature Range and its Recent Evolution. Brian Olsen April 20, 2006. Outline. Introduction to DTR Local Examples Global Trends What affects DTR? Conclusions. The Global Warming Signal. Multi-decadal “pause” in warming. IPCC, 2001. Diurnal Temperature Range (DTR).

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The Diurnal Temperature Range and its Recent Evolution

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  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 insummer SLC WFO

  5. KSLC Trends 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 • 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) StrongWarming Steady StrongWarming Warming Decreasing Steady Vose et al. 2005 Vose et al. 2005

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

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

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

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