| NATS 101 Lecture 31 Climate and Climate Change |
| Climate Overview |
| Climate classified largely in terms of | ||
| Temperature & Precipitation (vs. evaporation) | ||
| Koppen Climate Classification Groups |
| A. Topical Moist: no winter | |
| B. Dry: Potential evapotranspiration > precipitation | |
| C. Moist Mid-Latitude with mild winter | |
| D. Moist Mid Latitude with severe winter | |
| E. Polar: cold, T<10oC | |
| H. Highland | |
| Global map |
| More classification detail |
| Af Tropical rain forest | |
| Am Tropical monsoon | |
| Aw Tropical wet and dry | |
| BW Arid desert | |
| BS Semi-arid | |
| Cfa Humid subtropical | |
| Cfb Cfc Marine | |
| Cs Mediterranean dry summer | |
| Cw Dry winter | |
| What is Climate CHANGE? |
| Climate change - A significant shift in the mean state and event frequency of the atmosphere. | |
| Climate change is a normal component of the EarthÕs natural variability. | |
| Climate change occurs on all time and space scales. | |
| A plethora of evidence exists that indicates the climate of the Earth has changed. |
| Determining the Past Climate |
| Paleoclimatology - the study of past climates. | |
| Past 100-200 years (weather observations) | |
| Must use indirect climate measures, proxies, to examine further into the past. Some proxies: | |
| - Tree rings (1,000+ years before present BP) | |
| - Trapped pollen (10,000+ years BP) | |
| - Glacial ice cores (100,000+ years BP) | |
| - Ocean sediment cores (1 Million+ years BP) | |
| - Geology (1 Billion+ years BP) |
| Ice Core from Vostok, Antarctica |
| During last ice age (>18,000 years ago) | |
| Temps 6oC colder | |
| CO2 levels 30% lower | |
| CH4 levels 50% lower | |
| H2O levels were lower | |
| than current interglacial. | |
| What caused what? |
| Most Recent Ice Age |
| SST 18,000 years BP |
| Temperatures Since Last Ice Age |
| Climate Changes Affect Mankind |
| Evidence of Climate Change |
| Causes of Climate Change |
| Atmospheric Composition - Anything that changes the radiative properties of the atmosphere (volcanic aerosols, carbon dioxide). | |
| Astronomical - Anything that alters the amount or distribution of solar energy intercepted by the Earth (solar variations, orbital variations). | |
| EarthÕs Surface - Anything that alters the flow of energy at the Earth's surface or changes its distribution (desertification, continental drift). |
| Causes of Climate Change |
| Milankovitch Theory of Ice Ages |
| Attempts to explain ice ages by variations in orbital parameters | |
| Three cycles: | |
| Eccentricity (100,000 yrs) | |
| Tilt (41,000 yrs) | |
| Precession (23,000 yrs) | |
| Changes the latitudinal and seasonal distributions of solar radiation. |
| Milankovitch Theory of Ice Ages |
| Ice ages occur when there is less radiation in summer to melt snow. | |
| Partially agrees with observations, but many questions unanswered. | |
| What caused the onset of the first Ice Age? |
| Long-Term Climate Change |
| 250 million years ago, the worldÕs landmasses were joined together and formed a super continent termed Pangea. | |
| As todayÕs continents drifted apart, they moved into different latitude bands. | |
| This altered prevailing winds and ocean currents. |
| Long-Term Climate Change |
| Circumpolar ocean current formed around Antarctica 40-55 MY ago once Antarctica and Australia separated. | |
| This prevented warm air from warmer latitudes to penetrate into Antarctica. | |
| Absence of warm air accelerated growth of the Antarctic ice sheet. |
| Our changing climate |
| Slide 20 |
| Our changing climate |
| Our changing climate: Key Questions |
| Slide 23 |
| Our changing climate: Increasing CO2 concentrations |
| Changing CO2 concentrations |
| Ice Core from Vostok, Antarctica |
| During last ice age (>18,000 years ago) | |
| Temps 6oC colder | |
| CO2 levels 30% lower | |
| CH4 levels 50% lower | |
| H2O levels were lower | |
| than current interglacial. | |
| 130,000 years ago it was a bit warmer than today | |
| 50% change in CO2 associated with 8oC change in temperature | |
| 6-8oC decrease in temperature produced incredibly different climate: Ice Age |
| Slide 27 |
| Increasing CO2 concentrations |
| Our changing climate: Can we predict it? |
| GLOBAL Energy Flow Thru Atmosphere |
| Global Atmo Energy Balance |
| Global Atmo Energy Imbalance |
| Change in IR Emission to Space |
| Notice that because of EarthÕs greenhouse gases, 91% (=64/70) [195/235 = 83%] of the IR emitted to space comes from the atmosphere and only 9% (=6/70) [40/235 = 17%] comes from the surface | |
| When GHGÕs are added to the atmosphere, the altitude of IR emission to space rises | |
| In the troposphere, air temperature decreases with altitude | |
| So the temperature of the emission to space decreases | |
| So the energy emission to space decreases because the emission energy decreases with decreasing temperature |
| Change in IR Emission to Space |
| BEFORE GHG increase IN=OUT AFTER GHG increase |
| Change in IR Emission to Space (contÕd) |
| AFTER GHG increase IN>OUT Eventual solution IN=OUT |
| Complexity of Climate System |
| Closer Look at Climate System |
| Climate Feedback Mechanisms |
| Positive and Negative Feedbacks |
| Assume that the Earth is warming. | |
| - Warming leads to more evaporation from oceans, which increases water vapor in atmosphere. | |
| -More water vapor increases absorption of IR, which strengthens the greenhouse effect. | |
| -This raises temperatures further, which leads to more evaporation, more water vapor, warmingÉ | |
| ÒRunaway Greenhouse EffectÓ | |
| Positive Feedback Mechanism |
| Positive and Negative Feedbacks |
| Again assume that the Earth is warming. | |
| - Suppose as the atmosphere warms and moistens, more low clouds form. | |
| - More low clouds reflect more solar radiation, which decreases solar heating at the surface. | |
| - This slows the warming, which would counteract a runaway greenhouse effect on Earth. | |
| Negative Feedback Mechanism |
| Positive and Negative Feedbacks |
| Atmosphere has a numerous checks and balances that counteract climate changes. | |
| All feedback mechanisms operate simultaneously. | |
| All feedback mechanisms work in both directions. | |
| The dominant effect is difficult to predict. | |
| Cause and effect is very difficult to prove at the Òbeyond a shadow of a doubtÓ level. |
| Key Points: Climate Change |
| Proxy data are used to infer the past climate. | |
| Data show that the EarthÕs Climate | |
| Has changed in the past | |
| Is changing now | |
| And will continue to change | |
| Key question is determining whether recent changes are due to natural causes or man. |
| Key Points: Climate Change |
| The climate system is very complex. | |
| Contains hundreds of feedback mechanisms | |
| All feedbacks are not totally understood. | |
| Three general climate change mechanisms: | |
| Astronomical | |
| Atmospheric composition | |
| EarthÕs surface |
| Assignment for Next Lecture |
| Topic - Anthropogenic Climate Change | |
| Reading - Ahrens, p 391-399 | |
| Problems - 14.12, 14.15, 14.16, 14.19 | |
| NOVA: ÒWhatÕs Up with the Weather?Ó |