Climate Change in the Champlain Basin - The Nature Conservancy

Climate Change in the Champlain Basinemissions scenario. Although A2 represents an extremesituation relative to the B1 case, it represents a situation inwhich atmospheric CO2 accumulation continues atgradually accelerating rates over the course of this century.Because the Champlain Basin has already experienced awarming of 2.1°F (1.2°C) during the last three decades, itis therefore reasonable to conclude that the A2 path mightproduce an additional warming close to what most modelssuggest by century’s end; simply continuing the recent30-year trend steadily for another nine decades would raisetemperatures by another 6.3°F (ca. 3.5°C), within the modeled6–11°F range that is predicted for the A2 scenario.It is important, however, to remember that all projections offuture trends come with the caveat that year-to-year fluctuationswill also push temperatures well above or belowthe mean from time to time. Powerful short-term factorssuch as the North Atlantic Oscillation, shifts in stratosphericmoisture content, volcanic eruptions and random movementsof storm tracks will temporarily disrupt the moresmoothly rising tide of greenhouse warming as they havealways done in the past. As a result, changes from year toyear will sometimes be more dramatic than the long-termtrends and may even run counter to them for brief periodsof time without negating the usefulness of those underlyingtrends for long-term climatic prediction.Climatic “extremes” are also expected to become morecommon as the world warms (IPCC, 2007), but this doesnot necessarily mean that every aspect of variability willincrease in the Champlain Basin. Record-breaking coldsnaps, for example, may occur less often. Most of the thermalextremes might therefore appear in the form of recordhighs, which should naturally occur more often as theupper bounds of temperature variability rise along with themean. Such changes could be experienced as increasinglyfrequent and memorable heat waves during the warmermonths of the year and as deeper and/or more frequentthaws during winter.In summary, mean annual temperatures in the ChamplainBasin are likely to rise 1–11°F (roughly 0.5–6.1°C) by theend of this century, depending on which model simulationand emissions scenario is followed. One might alsospeculate that significant warming is most likely to occurduring winter on the basis of three lines of reasoning. First,dominant winter warming is predicted for the Northeast andChamplain Basin by most, though not all, of the AOGCMsrepresented through Climate Wizard for the A2 scenario(Table 3). Second, loss of cool, reflective snow and icecover due to melting may tend to amplify winter warmingin some locations, though the importance of this effect islikely to vary a great deal from site to site. And finally, winterweather in this region is strongly influenced by air massesthat move down from higher latitudes where warming ratesgenerally exceed the global average; the Champlain Basinmight therefore be exposed to maximally warmed highlatitudeair masses during the coldest periods of the year.Such arguments, however, are only tentative, and whenconsidering future climatic changes on a local scale it iswiser to anticipate a likely range of possibilities than tofocus too heavily upon a single anticipated outcome. Inaddition, although the universal projection of annual-scalewarming during this century is very likely to be correct, theconsistency among climate model projections for seasonalscalechanges is much weaker (Table 3) due to inherentlimitations in the ability of AOGCMs to simulate short-termclimate conditions, especially on local geographic scales(Hayhoe et al., 2007; Schiermeier, 2010). Furthermore, becausewe do not yet know how greenhouse gas emissionswill change in the future, we cannot be sure of exactly howmuch temperatures will rise, only that the general directionof change will be that of warming throughout the presentcentury. The model simulations presented here nonethelessallow us to estimate the range of annual-scale warming inthe Champlain Basin that is most reasonable to expect andprepare for.B. Precipitation: Past and futurePrecipitation is extremely variable in space and time, andfuture precipitation patterns are therefore more difficultto model and predict than temperature trends. However,broad-scale patterns of change are relatively easy to envision.As global warming continues, the amount and intensityof precipitation is expected to increase in much of the worldas heat-driven atmospheric circulation systems strengthen,and as evaporation from warmer land and ocean surfacesraises the moisture content of the air (IPCC, 2007). NECIApredicted an increase of total annual precipitation in theNortheast by the end of this century, on the order of 10% orso (Frumhoff et al., 2007). In addition, more winter precipitationis expected to fall as rain rather than as snow as warmingcontinues throughout this century (Frumhoff et al., 2007;Hayhoe et al., 2007).Total annual precipitation in the Champlain Basin increasedby about 3 inches during the early 1970s due to a rapidupward shift to a higher average baseline that has persistedto the present day (Figure 3). But apart from this, there islittle evidence of a direct correspondence between risingtemperature and the amount of precipitation revealed12