Climate Change in the Champlain Basin - The Nature Conservancy

What natural resource managers can expect and doIV. Findings: Temperature, precipitationand physical changesA. Air temperatures: past and futureThe planet as a whole warmed by 1.3°F (0.7°C) during the20th century, with human-generated greenhouse gasesdriving most of that change since the 1970s (IPCC, 2007).However, the global trend does not necessarily representclimatic changes that have occurred at local scales; temperaturesin some areas of the world have warmed fasteror cooled slightly on average during the last half century.In our region, the Northeast Climate Impacts Assessment(NECIA) and other sources have found that the northeasternstates as a whole warmed by 1.4°F (0.8°C) over thecourse of the 20th century (Frumhoff et al., 2007; Hayhoeet al., 2007; Jacobson et al., 2009). Between 1970 and2000, regional average temperatures rose more rapidly (ca.1.3°F in 30 years), with the bulk of the warming occurringin winter. By the end of this century, mean temperaturesin the Northeast are expected to rise another 5–10°F (ca.3–5°C), depending upon the models and emissions scenariounder consideration (Hayhoe et al., 2007).Regional warming here has been slightly fasterthan the global average, and the overall shapesof the rising temperature curves in most of theNortheast, including the Champlain Basin, differedsomewhat from the global pattern during much ofthe last century (Figure 1). This highlights the importanceof considering smaller geographic scalesin addition to globally averaged conditions, and italso means that the selection of appropriate timeframes for analysis must be undertaken with care.Both the global and regional temperature recordsshow a temporary high in the mid-20th centuryfollowed by a decade or so of cooling before thelong-term rising trend resumed in the 1970s. However,the mid-century high occurred later here (ca.1950s) than it did for the planet as a whole (ca.1940s). Because of that pattern, records of temperaturesin the Northeast that begin in the 1950s canproduce surprisingly weak linear warming trends or evenslight overall cooling at sites where the mid-century peakhas not yet been exceeded by today’s rising temperatures.Conversely, shorter time windows that begin in the relativelycool 1960s produce rising trends that are steeper than thecentury-scale average. How does one most reasonablyselect the proper time frame for determining how climatehas changed in the recent past?For this study, we selected the 30-year, 1976-2005 intervalfor most of our historical analyses for three reasons.First, 30 years is the standard period used for calculationof a region’s current climate. Second, it represents a timeframe that has been analyzed elsewhere in the region,so it provides opportunities for comparison. And finally, itrepresents conditions that have been clearly influencedby greenhouse gas buildups. Before the 1970s, additionalfactors such as solar variability and aerosol concentrationsmore strongly disrupted the global warming trend,but since then, only greenhouse gas concentrations haverisen in concert with temperature (IPCC, 2007). Becausegreenhouse gas concentrations are expected to rise furtherin coming decades, the climatic record of the 1976–2005interval provides a useful guide to the general nature ofchanges that are soon to come.Figure 1. Global and Champlain Basin temperatures,1900–2008. Dotted lines bracket the 1976-2005 timeinterval. Arrows indicate general directions of changeover selected time intervals. Note the difference in timingof the mid-century warm periods in the two records;the global peak occurred a decade earlier than the onein the Champlain Basin.9