Global Warming is a Fact of Life

Transcription

1 RECENT HISTORICAL TEMPERATURE AND TRADE-WIND INVERSION VARIATIONS IN HAWAI I Global Warming is a Fact of Life Tom Giambelluca Geography UH Manoa : o C per decade : o C per decade FAQ 3.1, Figure 1 High-latitudes: +2.3 o C Tropics: +0.8 o C Expectations and observations of warming shift attention to higher latitude land areas However, while land areas have warmed fastest at high latitudes, warming of the Pacific Ocean shows cyclical patterns with respect to latitude Pacific Decadal Oscillation (PDO) El Niño-Southern Oscillation (ENSO) ; also see Mantua et al. (1997) and Power et al. (1999) ; also see Trenberth and Caron (2000) 1

2 Temperature Observations in Hawai i Temperature Trends at Long-Record Stations Sea Level Recent Temperature Trends High Elevation Source: Giambelluca and Luke (2007) Source: Giambelluca and Luke (2007) Selected Temperature Stations Hawai i Temperature Index GLOBAL TRENDS: : o C per decade : o C per decade 2

3 HTI PDO SST PDO Faster Warming at High Elevations: Predicted by Models SST Source: Bradley, Vuille, Diaz, and Vergara (2006) Faster Warming at High Elevations: Observed High- Minus Low-Elevation in Hawai i Source: Diaz and Eischeid (2007) Hot Nights! Decrease in Day-Night Temperature Difference All Stations Low-Elevation High-Elevation Trend ( o C per decade) Minimum Temperature 0.278* 0.153* 0.441* *Significant at p = 0.5 Maximum Temperature

4 Global Trends Why is T min Increasing Faster? One possible explanation would be increasing cloud cover More clouds would: 1. Offset daytime warming by reducing solar heating 2. Increase nighttime heating by trapping longwave radiation. Is Cloud Cover Increasing? Is Cloud Cover over Hawai i Changing? Since about 1950: Many continental areas: Increasing total cloud cover USA: Increasing at 1.4% per decade China, Italy, central Europe: Decreasing cloudiness Upper level cloud cover decreased over ocean in low latitudes Changes in lowerlevel cloud cover uncertain (satellite) Source: Norris (2005) Is Cloud Cover over Hawai i Changing? Implications of Warmer Nights Solar radiation is increasing at Haleakalā summit since 1990 Net radiation uncertain, but probably increasing Increasing cloudiness at night is a possibility Source: Reduced comfort level Increased energy use for AC? Most agricultural crops in non-frost areas are negatively affected by higher nighttime temperatures, because of increased respiration Same is true for natural vegetation Shift may favor some invasive plants over natives 4

5 Trade-Wind Inversion (TWI) Mean altitude ~2200 m (7200 ) Frequency ~80% Stable atmospheric layer Forms a barrier to rising air Because rising air is the predominant means by which clouds form, cloud development is capped at the TWI level As a result, relatively thin clouds produce less precipitation when TWI is present Climate changes resulting in either more frequent or lower altitude TWI will cause a reduction in rainfall TWI Knowing the effects of global warming on TWI frequency and height is key to predicting the local climatic, hydrological, and ecological impacts of global warming in Hawai i. Photo: John DeLay Effect of Inversion on Rainfall HaleNet: Haleakalā Maui Guangxia Cao (2007): 1. Analyzed TWI variability during past 25 years: Strong evidence of upward trend in TWI frequency Weak evidence of downward trend in TWI height 2. Found relationships between TWI and broad atmospheric variables 3. Used global climate model simulations to show that TWI may become more frequent and lower under global warming Source: Adapted from Tran (1995) Source: Cao (2007) Source: Cao et al. (2007) 5

6 Hawai i (winter) Rainfall Index (HRI) Source: Chu and Chen (2005) Main result suggests that TWI frequency of occurrence has increased during the past 25 years Will this trend persist, or is it part of a multi- decadal oscillation? If the trend does persist: Reduced rainfall overall will continue Drought may be more severe above the inversion level, intensifying the climatic and ecological gradient there Alpine and sub-alpine ecosystems would be most severely impacted What Should We Do? Climate and biological monitoring is essential Efforts to predict global change effects on Hawai i s future climate should be on-going Efforts also needed to understand impacts of these changes on hydrology and ecology Prepare for warmer climate Prepare for a possible drier climate Be part of global mitigation efforts THANK YOU 6