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The Diurnal Temperature Range and its Recent Evolution

This document explores the concept of Diurnal Temperature Range (DTR), defined as the difference between high and low temperatures within a 24-hour period. It examines local examples and global trends from 1950 to 2004, highlighting the warming signal and recent unique trends, including a "pause" in global warming. The relationship between urban heat islands, climate variables, and DTR is analyzed, with a focus on how minimum temperatures have increased disproportionately to maximums, leading to a decrease in DTR. The report emphasizes the challenges in measuring DTR trends amidst local and global variability.

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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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