2001
12 Currents & UpwellingProj: A weakening of the global thermo-haline circulation may occur, reducing heat transport to the N. AtlanticCompeting arguments on oceanic & coastal upwelling increase or decreaseNo reliable forecastsForces driving natural variability not well understoodCurrents and upwelling. Freshwater influx from the movements and melting of sea ice or ice sheets may lead to a weakening of the global thermohaline circulation, leading to cooling in the North Atlantic and possibly causing unpredictable instabilities in the climate system. There are competing arguments as to whether oceanic and coastal upwelling would increase or decrease. In any case, there is no ability to make reliable forecasts at the regional scale which governs the upwelling systems. Forces leading the oceans to vary in temperature and currents on decadal scales of natural variability are not well understood and are not well modelled.
13 Ocean Conveyer BeltSource: US National Assessment
14 Storms and El NiñoObs: No trends in storminess in last 50 years. Some regional trends in storminess in both directionsThe post 1989 period of ENSO activity seems unusually high, but may have happened beforeProj: Changes in frequency & intensity of cyclones, storms, & El Niño uncertain
15 Ice CoverObs: Two weeks less fresh ice in last ~125 yrs. No evident trend in sea ice in Antarctic.Proj: Glaciers and snow and ice coverage to continue retreat in N. hemisphere. Major loss of fresh & sea iceThe NW Passage & N. Sea Route of Russia may have 100 days of shipping. 40% thinner summer Arctic ice since ~1960In the Antarctic, the main effect will be a retreat of the ice edgeIce coverage impacts ice-associated species, primary productivity, fishing and aquaculture
16 Sea Level RiseObs. show cm. rise since 1900; 1-2 mm/yr. 10X faster than previous 3K yrs. No acceleration detectedProj. is cm by 2100; from thermal expansion & melting of ice. USNA*: +19” by 2100Regional variations due to wind and atmospheric pressure, ocean density, land motion, currentsWetlands will decrease; sharply where there is shore protectionHigher wave energy; faster erosion*USNA= US National Assessment
19 PrecipitationObs show several %/decade greater air moisture & precip up 1%/decade in mid-high latitudesProj: A few percent increaseMore extreme, heavier precip eventsThis can affect water salinity, watershed flows, turbidity, pollutant loading and related factors
20 7 of 9 Models Agree on Wetter Winters in Northeast Source: IPCC 2001
21 UV-B Other groups, not IPCC, study ozone depletion Obs: ozone losses up in mid-latitudes & ArcticGrowth rates of several problem chemicals have slowed or stopped. Peak may be pastProj: ozone layer may return to normal about 2050In clear waters, UV-B penetrates tens of meters, damaging eggs, larvae and zooplanktonIn coastal waters, less than 1 meterAntarctic ozone hole is larger than Antarctica
22 Species Sensitivities • Changes: temperature, sea level, river flows, salinity, currents, winds, storms, and variability• Species are dependent on one or more of above• Species can move rapidly if habitat and paths exist• Fish are cold-blooded. Life processes, like growth, are faster when warmer (within limits)• Many species have narrow ecological niches, but there are many species to fill niches• Small changes cause large disruptions to a species• Mixes will change until stability is reestablishedMany of the changes affect predator - prey relationships
23 Societal Sensitivities • Species in more stable environments are usually more valuable• Fishers can follow fish, communities won’t• Political borders or economics stop pursuit• Developing nations dependent on fish as food or export earnings are most sensitiveFishers can follow fish, communities usually won’t-But there are economic,social and safety costs
24 Sensitivity Examples Species Societal • Scallop and fish eggs that rely on a gyre to return them to their habitat on a certain day or week• Fish eggs in streams or on the sea floor that require a minimum current speed for oxygenation• Species that require a