Weather and Climate Change
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
Rain drop size and shape
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
Air Mass Source Regions summer only
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.
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
Air Mass Fronts Figure 12.12 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. http://www.rap.ucar.edu/weather/satellite/
Cold Fronts: cold, fast, steep and stormy
Warm Fronts: warm, slow and wet
Air Mass Fronts Figure 12.12 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. http://www.rap.ucar.edu/weather/satellite/
Severe Thunderstorm Structure
Severe Thunderstorms Figure 15.5
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)
Ice Ages in the Geologic Past Global Cold Warm Cold Warm We are in a warm interval (interglacial) of a cold period (Ice Age)
Milankovitch Cycles
Interglacial Glacial
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?
Ice cover during the last Glacial Maximum
Glacial Advance in Montana
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.)
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!!
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
What s Missing? Answer: An Atmosphere with Greenhouse Gases, e.g. water vapor, carbon dioxide, methane, nitrous oxide
Greenhouse Effect Increasing Greenhouse Gases increases the amount of heat absorbed by the atmosphere and re-radiated back to the Earth surface.
What are the trends in temperature?
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
Last 140 years Last 1000 years Recent warming
The last millenium
Recent Centuries
Observed Temperature Trends
What are the trends in greenhouse gas concentrations in the atmosphere?
Steady State until the Industrial Revolution The rest of the slides are from the most recent IPCC report (2007)
Recent Increases in Carbon Dioxide Human activities have caused dramatic increases in greenhouse gas concentrations
What are the sources of anthropognic carbon dioxide?
Power
Transportation
Nightlights
Nightlights
Greenhouse gas emitters
What is causing the warming?
What is causing climate change?
What about the future?
CO 2 Emission Scenarios What people may do
The Impact on CO 2 Concentrations
The Impact on Global Temperature
Can natural factors explain recent warming? With anthropogenic effect? Without anthropogenic effect? How good are our climate models? Or Are humans to blame
What about changes in sea level? Over Figure the last 5.13 century Increase of ~15 centimeters
Sea level rise Global average sea level rose 0.1-0.2 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
Sea level over the next 100 years Increase of ~20 to 50 centimeters Range of estimates
Predicted temperature increases In ~ 100 years ~ 2-5 increase in T in Montana over the next century High latitudes and land affected most
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)
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 1.7-2.3 million acres by 2060 Increased acidity of the ocean will make life impossible for corals. Possible extinction in the next 100-150 years! (Other calcareous marine organisms?)
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)
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.