AMS Weather Studies Introduction to Atmospheric Science, 4th Edition

AMS Weather Studies Introduction to Atmospheric Science, 4th Edition
Chapter 15 Climate and Climate Change © AMS

Case-in-Point The consensus of scientific opinion is that the present global warming trend is largely anthropogenic in origin Human activity, principally the combustion of fossil fuels, is responsible for the build-up of carbon dioxide and other infrared-absorbing gases in the atmosphere The amount of anthropogenic CO2 already emitted into the atmosphere ensures a magnitude of warming that will cause an unacceptable rise in sea level in some localities The 2007 IPCC Fourth Assessment Report estimates that msl will be 0.2 to 0.6 m higher than now by the year 2100 An example of an island nation that is particularly vulnerable to rising sea level is the Maldives Migration may be their only alternative © AMS

Driving Question How and why does climate change?
Climate changes over a broad range of time scales Years, decades, centuries, millennia Many forces working together are responsible for climate change Variability in available solar energy Volcanic eruptions Changes in the Earth’s surface properties Human activities © AMS

Earth’s Climate System
Climate: The weather of some locality averaged over some time period plus extremes in weather Varies spatially and temporally Described quantitatively in terms of: Normals Means Extremes Weather elements including wind, temperature and precipitation NOAA’s National Climatic Data Center (NCDC) Collects (from NWS), processes and archives data Makes available to users © AMS

The Climatic Norm Average value of some climatic element Encompasses the total variation in the climate record, including both averages plus extremes Computed averages of weather elements over a 30-year time period Adjusted every 10 years to add the latest decade and drop the oldest In the U.S. 30-year averages only done for temperature, precipitation and air pressure © AMS

Climatic Anomalies Departures from long-term climatic averages Positive anomalies: above long-term averages Negative anomalies: below long-term averages Precipitation anomalies usually form more complex patterns than temperature anomalies Due to greater spatial differences in precipitation arising from: Variability of storm tracks Almost random distribution of convective showers Middle and high latitudes have a geographic non-uniformity of climatic anomalies Due to prevailing westerly wave pattern Geographic non-uniformity also applies to trends in climate © AMS

Climate Boundary Conditions
Boundary conditions are imposed on climate due to: Latitude Elevation Topography Proximity to large bodies of water Earth’s surface characteristics Long-term average atmospheric circulation Prevailing ocean circulation © AMS

Latitude Incoming solar radiation and length of daylight vary Earth’s surface temperature responds to these variations Elevation Temperature drops with increasing elevation Topography Affects the distribution of clouds and precipitation Proximity to large bodies of water Important in storage and exchange of heat, water, and greenhouse gases Earth’s surface characteristics Ocean vs. Land, vegetative cover, semi-permanent snow and ice Influence the amount of incident solar radiation that is converted to heat © AMS

Atmospheric Circulation Encompasses influence of all weather systems Less regular and less predictable than other facts Prevailing Ocean Circulation Influences radiational heating and cooling of the planet Primary control of the amount of solar radiation absorbed at the Earth’s surface Ocean is the main source of the most important greenhouse gas (water vapor), major regulator of CO2 Transfers heat from lower to higher latitudes © AMS

Global Climate Patterns
Temperature Latitude of highest mean annual surface temperature (heat equator) located about 10° north of the geographical equator Heat equator is located in the Northern Hemisphere Polar regions have different radiational characteristics Arctic is warmer than Antarctic: Arctic is mostly ocean, Antarctic is ice sheets with a higher albedo Northern Hemisphere has more land then the Southern Hemisphere Land warms much faster than water Ocean circulation transports more warm water to the Northern Hemisphere then the Southern Hemisphere © AMS

Temperature, continued Systematic patterns appear in January/July temperatures Isotherms tend to parallel latitude circles Isotherms shift north and south from January to July following the Sun Greater shift over land Steeper isothermal gradients mean more vigorous circulation and stormier weather in the winter hemisphere © AMS

Mean sea-level air temperature for January in °C © AMS

Mean sea-level air temperature for July in °C © AMS

Precipitation Variability in patterns due to: Topography Distribution of land and sea Planetary-scale circulation Intertropical Convergence Zone (ITCZ) Rainfall in the adjacent belt poleward to about 20° latitude depends on seasonal shifts of the ITCZ Subtropical anticyclones Dominate climate all year between 20° to 35° N and S Prevailing wind patterns Between about 35° and 40° latitude, the prevailing westerlies and subtropical anticyclones govern precipitation Precipitation generally declines poleward of about 40° latitude as lower temperatures reduce the amount of precipitable water Tendency in continental interiors for more precipitation in the summer © AMS

Mean annual precipitation (rain plus melted snow) in millimeters (mm) © AMS

Climate classification Classification schemes group climates according to: Meteorological basis of climate Asks why climate types occur where they do Environmental effects of climate Infers the type of climate from environmental indicators such as the distribution of indigenous vegetation Numerical climate classification schemes also employed that utilize statistical techniques © AMS

The Climate Record Climate varies from place to place and with time
Reconstructions of past climate based on historical documents, and longer-term geological and biological evidence Geological Time General conclusions made regarding climate over geological time Geological past subdivided using geologic time scale Plate tectonics complicates climate reconstruction by moving continents and opening and closing ocean basins Continental drift Alters the course of heat-transporting surface ocean currents and the ocean conveyor-belt system © AMS

Geologic time scale © AMS

The Climate Record About 225 million years ago, the super-continent Pangaea began to split apart into separate continents that slowly drifted apart. Ocean basins opened, and eventually continents reached their present positions. Continental drift is responsible for climate changes operating over hundreds of millions of years © AMS

The Climate Record Geologic time, continued
570 million years ago, between Proterozoic and Phanerozoic Eons: abrupt climatic changes between extreme cold and tropical heat. Global warming. Mesozoic Era, from about 245 to 70 million years ago, remained relatively warm Global mean temperature rose 3 - 4°C between Triassic and Jurassic Periods Creaceous Period saw temperatures 6 - 8°C higher then now Cenozoic Era, 55 million years ago, methane released by deep sea sediments enhanced the greenhouse effect 40 million years ago saw shift toward colder, drier and more variable climate © AMS

The Climate Record Past Two Million Years
Plate tectonics not a major factor Climate has favored the development of glacial ice sheets Glacial theory Pleistocene Ice age began 1.7 million years ago, and culminated about 10,500 years ago The Pleistocene included glacial and non-glacial events Ice sheets caused sea level to drop by 113 to 135 m (370 to 443 ft) Land bridge was exposed linking Siberia and Alaska During interglacial episodes, ice sheets thinned and retreated, sometimes disappeared entirely During glacial episodes temperatures were cooler than today, but cooling was not geographically uniform Polar amplification: an increase in the magnitude of a climatic change with increasing latitude © AMS

The Climate Record Variation in global glacial ice volume from the present back to about 600 million years ago Temperature variation over the past 160,000 years © AMS

The Climate Record Extent of glacial ice cover over North America about 20,000 to 18,000 years ago, the time of the last glacial maximum © AMS

The Climate Record Past Two Million Years, continued
Fluctuations between major glacial and interglacial climatic episodes over the past 600,000 years Last major glacial climatic episode began about 27,000 years ago, reaching its peak about 18,000 to 20,000 years ago Present interglacial known as the Holocene © AMS

The Climate Record Past Two Million Years, continued
Over the past 1000 years, there has been a Medieval Warm Period (about 950 to 1250 CE) followed by a cooling known as the Little Ice Age (about 1400 to 1850 CE) © AMS

The Climate Record Instrument-Based Temperature Trends
Invention of weather instruments and establishment of weather observing networks made climate record much more detailed and dependable Highest confidence is in temperature records dating from the late 1800s with the birth of national weather services along with the founding of the International Meteorological Organization (WMO today) Examination of temperature trends over the past 140 years or so is instructive as to climate variability and climate change General consensus in the scientific community holds that an overall global-scale warming trend has prevailed since the end of the Little Ice Age © AMS

Lessons of the Climate Past
Climate is inherently variable over a broad spectrum of time scales ranging from years to decades, to centuries, to millennia Variations in climate are geographically non-uniform in both sign (direction) and magnitude Some areas may experience warming while others cooling Climate change may consist of a long-term trend in various climate elements and/or a change in the frequency of extreme weather events Climate change tends to be abrupt rather than gradual Abrupt means change is shorter than duration of episodes © AMS

Lessons of the Climate Past
Only a few cyclical variations can be discerned from the long-term climate record Regular cycles: diurnal and seasonal variations, incoming solar radiation Quasi-regular variations: El Niño, Holocene millennial-scale fluctuations, major glacial-interglacial shifts Climate change impacts society © AMS

Causes of Climate Change
Match a possible cause (or forcing) with a specific climatic oscillation (or response) based on similar periods of oscillation Example: El Niño may account for climate shifts lasting several months Global energy budget Changes in energy input/output will change the planet’s climate © AMS

Climate and Solar Variability Earth’s climate system can be altered by fluctuations in the Sun’s energy output, sunspots, or regular variations in Earth’s orbital parameters A sunspot is a dark blotch on the face of the Sun that develops where an intense magnetic field suppresses the flow of gases transporting heat from the Sun’s interior Typically last for a few days, total number varies systematically Satellite monitoring reveals that Sun’s energy output varies directly with sunspot number © AMS

Variation in mean annual sunspot number © AMS

Earth’s Orbit and Climate Change Milankovitch Cycles Regular variations in the precession and tilt of Earth’s rotational axis and the eccentricity of its orbit around the Sun Caused by gravitational influences exerted on the Earth by other large planets, the moon and sun Tilt of Earth changes from 22.1° to 24.5° over about 41,000 years © AMS

Past and future variations in the Milankovitch cycles
© AMS

Volcanoes and Climate Change Only explosive eruptions rich in sulfur dioxide (SO2) are likely to impact global or hemispheric climate for a few years at the most When combining with water vapor, droplets of sulfuric acid (H2SO4) and sulfate particles form; together called sulfurous aerosols Can remain in stratosphere for many months Collectively thicken the stratospheric aerosol veil Absorb both incoming solar and outgoing infrared radiation, warming the lower stratosphere In the presence of chlorine destroy ozone © AMS

Volcanoes and Climate Change
Temperature anomalies in Fahrenheit degrees in the Midwest during June, July, and August 1992 © AMS

Volcanoes and Climate Change The combination of stratospheric warming and ozone depletion strengthens the circumpolar vortex This is associated with a non-uniform change in surface temperatures A violent sulfur-rich eruption is unlikely to lower the mean hemispheric or global temperature by more then 1 °C Local and regional temperature change may be greater Large scale cooling followed massive volcanic eruptions that emitted SO2 into the stratosphere © AMS

Earth’s Surface Properties and Climate Change Earth’s surface, comprised of approximately 71% ocean water, is the prime absorber of solar radiation Changes in the physical properties of water or land surfaces, or relative distribution of ocean, land or ice may affect Earth’s radiation budget and climate Variations in snow cover Snow has refrigerating effect on atmosphere Reflects 80% of solar radiation reducing solar heating Emits infrared radiation, radiating heat to space © AMS

Earth’s Surface Properties and Climate Change, continued Changes in sea ice or glacial ice coverage have longer-lasting impacts on climate Ice is much more reflective of incident solar radiation than ocean or snow-free land Changes in sea surface temperature and ocean circulation SST patterns can exert a strong influence on the location of major features of the atmosphere’s planetary scale circulation Ocean circulation transports heat throughout the world; changes in circulation patterns can cause changes in climate © AMS

Human Activity and Climate Change Modification of the landscape Clearing forests, urbanization Alters radiative properties of the Earth’s surface Combustion of fossil fuels Alters concentrations of gases and aerosols Rising concentrations of CO2 and other infrared-absorbing gases enhance greenhouse effect, contributing to global warming Rapid rise in CO2 with start of Industrial Revolution Rise of other infrared-absorbing gases (e.g., methane and nitrous oxide) could also enhance greenhouse effect Methane is a product of organic decay in the absence of oxygen Nitrous oxide increase likely due to industrial air pollution © AMS

The Climate Future Global Climate Models (GCMs)
Simulate Earth’s climate systems Use mathematical equations that describe physical interactions among the various components of the climate system Differ from numerical models in that GCMs predict broad regions of expected positive and negative temperature and precipitation anomalies and mean locations of circulation features For example, used to predict potential climatic impacts of rising levels of greenhouse gases using boundary conditions GCMs are in need of considerable refinement May miss important feedback processes Need a greater resolution © AMS

The Climate Future Search for Cycles and Analogs
Climate records an alternative approach to predicting climate future Instrument-based and reconstructed climate record probed in search of regular cycles that might be extended into the future, and analogs that show how the climate in specific regions responds to global-scale climate change Identification of any statistically significant periodicities or trends in the climate record would be a powerful tool in climate forecasting © AMS

The Climate Future Enhanced Greenhouse Effect and Global Warming
Over the next 10, ,000 years, Milankovitch cycles favor return of Ice Age conditions Rising concentrations of greenhouse gases are likely to cause global warming to continue throughout this century Climate models predict that over the subsequent 20 years, the global mean annual temperature will increase at an average rate of about 0.2 Celsius degrees per decade Even if greenhouse gas emissions were to stabilize at present levels, global warming would likely continue well beyond the 21st century © AMS

Potential Impacts of Global Climate Change
Shrinking Glaciers and Rising Sea Level Persistence of the current global warming trend appears likely to cause sea level to rise in response to melting of land-based polar ice sheets and mountain glaciers, coupled with thermal expansion of seawater Amplification of the warming trend at higher latitudes would threaten the ice sheets of Antarctica and Greenland Melting could cause a considerable rise in sea level © AMS

Shrinking Glaciers and Rising Sea Level, continued The shrinkage of mountain glaciers and ice fields whose seasonal would be a major concern, as people, livestock, and crops rely on the season runoff for fresh water Thermal expansion of warming seawater will be a greater contributor to mean sea level rise than melting of land-based glaciers during the 21st century Higher mean sea level would accelerate coastal erosion, inundate wetlands, estuaries, and islands, and make coastal zones more vulnerable to storm surges © AMS

Arctic Environment Shrinkage of Arctic sea ice is likely to trigger an ice-albedo feedback mechanism that would accelerate melting of sea ice and amplify warming As sea ice cover shrinks, the greater area of ice-free ocean waters absorbs more solar radiation, sea-surface temperatures rise, and more ice melts Less sea ice cover on the Arctic Ocean is likely to increase the humidity of the overlying air leading to more cloudiness © AMS

Other Impacts Higher temperatures and more frequent drought may affect food production Possible concern for an increase in hurricane intensity High SST only one factor contributing to tropical cyclone formation Improved models of the climate system are needed to better assess the effect of warming on hurricane activity © AMS

Ocean Acidification CO2 that is absorbed by the ocean participates in chemical reactions that increase the acidity (lowers the pH) of ocean waters Potentially harmful to marine organisms that use carbonate ions (CO3-2) to build calcium carbonate (CaCO3) shells or skeletons Marine organisms that are particularly vulnerable to ocean acidification are coccolithophorids, foraminifera (phytoplanktonic organisms), and pteropods (small marine snails) All important food source in marine food webs Corals which filter plankton from ocean water and secrete calcium carbonate are also vulnerable © AMS

AMS Weather Studies Introduction to Atmospheric Science, 4th Edition

Similar presentations

Presentation on theme: "AMS Weather Studies Introduction to Atmospheric Science, 4th Edition"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

AMS Weather Studies Introduction to Atmospheric Science, 4th Edition

Similar presentations

Presentation on theme: "AMS Weather Studies Introduction to Atmospheric Science, 4th Edition"— Presentation transcript:

Similar presentations

About project

Feedback