Weather and Climate Change

Transcription

1 Weather and Climate Change

2 What if the environmental lapse rate falls between the moist and dry adiabatic lapse rates? The atmosphere is unstable for saturated air parcels but stable for unsaturated air parcels This situation is termed conditionally unstable This is the typical situation in the atmosphere Conditionally unstable air

3 Rain drop size and shape

4 At mid and northern latitudes most precipitation is formed via ice crystal growth Supercooled cloud drops and ice crystals coexist for 40º < T < 0º C Lack of freezing nuclei to glaciate drops Ice crystals can grow by Water vapor deposition Capture of cloud drops (accretion/riming) Aggregation Precipitation and the ice crystal process

5 Air Mass Source Regions summer only

6 Billings rain shadow cp air from Asia and frozen polar regions is carried across the Pacific, circulating around Aleutian low Contact with the ocean warms and moistens the air near the surface, transforming it to an unstable mp air mass As the mp air moves inland it crosses several mountain ranges, removing moisture as precipitation The drier mp air is transformed back to cp air as it travels across the cold, elevated interior of the U.S.

7 Fronts A Front - is the boundary between air masses; normally refers to where this interface intersects the ground (in all cases except stationary fronts, the symbols are placed pointing to the direction of movement of the interface (front) Warm Front Cold Front

8 Air Mass Fronts Figure Two air masses entering a region, such as the U.S. middle latitudes, have a front, or transition zone, between the strong temperature and humidity differences. Four different fronts are used on weather maps.

9 Cold Fronts: cold, fast, steep and stormy

10 Warm Fronts: warm, slow and wet

11 Air Mass Fronts Figure Two air masses entering a region, such as the U.S. middle latitudes, have a front, or transition zone, between the strong temperature and humidity differences. Four different fronts are used on weather maps.

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13 Severe Thunderstorm Structure

14 Severe Thunderstorms Figure 15.5

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17 Climate Change Climate defined as The accumulation of daily and seasonal weather events over a long period of time Climate can change on various time and spatial scales Years to decades to centuries; Ice ages and Glacial/Interglacial cycles, Both global and regional climates are affected Factors Natural Anthropogenic (man made)

18 Ice Ages in the Geologic Past Global Cold Warm Cold Warm We are in a warm interval (interglacial) of a cold period (Ice Age)

19 Milankovitch Cycles

20 Interglacial Glacial

21 Atmospheric CO 2 and Temperature Interglacial Warm Glacial Cold CO 2 and temperature covary over Glacial-Interglacial cycles, but which is the cause and which is the effect?

22 Ice cover during the last Glacial Maximum

23 Glacial Advance in Montana

24 What controls global temperatures on human timescales? (decades to centuries) Changes in concentrations of Greenhouse Gases (CO 2, H 2 O, CH 4 etc.) Changes in land use (farming to urban, forest to grassland etc.)

25 The Earth s Radiation Balance Incoming Energy = Outgoing Energy (absorbed sunshine) (area) = (thermal loss) (area) S(1-a) pr 2 = s T 4 (4 pr 2 ) Solve for T T = -18 C!!

26 The radiative equilibrium temperature The equilibrium surface temperature for Earth should be -18 C (~0 F) But, the observed surface temperature is ~ +15 C (~60 F) ~ 33 C warmer

27 What s Missing? Answer: An Atmosphere with Greenhouse Gases, e.g. water vapor, carbon dioxide, methane, nitrous oxide

28 Greenhouse Effect Increasing Greenhouse Gases increases the amount of heat absorbed by the atmosphere and re-radiated back to the Earth surface.

29 What are the trends in temperature?

30 Observed climate through the ages Throughout much of earth s history the temperature was warmer than today Warm periods of hundreds of millions of years interrupted by glacial periods Most recent series of Ice Ages began about 2 million years ago Recent N. American glaciers at maximum ~ 18,000 years ago

31 Last 140 years Last 1000 years Recent warming

32 The last millenium

33 Recent Centuries

34 Observed Temperature Trends

35 What are the trends in greenhouse gas concentrations in the atmosphere?

36 Steady State until the Industrial Revolution The rest of the slides are from the most recent IPCC report (2007)

37 Recent Increases in Carbon Dioxide Human activities have caused dramatic increases in greenhouse gas concentrations

38 What are the sources of anthropognic carbon dioxide?

39 Power

40 Transportation

41 Nightlights

42 Nightlights

43 Greenhouse gas emitters

44 What is causing the warming?

45 What is causing climate change?

46 What about the future?

47 CO 2 Emission Scenarios What people may do

48 The Impact on CO 2 Concentrations

49 The Impact on Global Temperature

50 Can natural factors explain recent warming? With anthropogenic effect? Without anthropogenic effect? How good are our climate models? Or Are humans to blame

51 What about changes in sea level? Over Figure the last 5.13 century Increase of ~15 centimeters

52 Sea level rise Global average sea level rose m during 20 th century Warmer temperatures associated with sea level rise due to Thermal expansion Melting of continental and Greenland ice Break-up and melting of Antarctic ice sheet

53 Sea level over the next 100 years Increase of ~20 to 50 centimeters Range of estimates

54 Predicted temperature increases In ~ 100 years ~ 2-5 increase in T in Montana over the next century High latitudes and land affected most

55 Predicted changes in precipitation in 100 years In global model simulations, Montana is right on the cusp of increased rain (Canada) and drought (the central plains)

56 Biological impacts Each 1 o C of warming shifts temperature zones by about 100 miles northward (or 500 feet in elevation) Many plant and animal species are unable to migrate fast enough to find suitable habitats Natural or man-made barriers may block natural migration of both animals and people An increase of 3 o C could threaten 7-11% of North America s plant species Loss of cold-water fish habitat of million acres by 2060 Increased acidity of the ocean will make life impossible for corals. Possible extinction in the next years! (Other calcareous marine organisms?)

57 Anthropogenic climate change will persist for a long time Temperature increases and rising sea level projected to continue for hundreds to thousands of years (IPCC, 2000) Melting of ice sheets contributes to sea level rise for thousands of years after climate has been stabilized (IPCC, 2000) A local warming > 3 o C, if sustained for millennia, would lead to essentially a complete melting of the Greenland ice sheet and a resulting sea level rise of 7 m Collapse of West Antarctic ice sheet would raise sea level ~ 70 m! Availability of clean, fresh water will be the most important environmental and geopolitical consideration for the next century, (regardless of climate change, but it could exacerbate the problem)

58 What should we do? Wait and see Take action Study the problem further before taking action It is a balance between Risk and Reward You need to become informed. Don t pass on ignorance on this important question.