| NATS 101 Lecture 32 Climate Change (contÕd) |
| Outline |
| IPCC summary from Kevin Trenberth | ||
| Current energy flow and balance | ||
| How changing the GHG concentrations causes climate to change | ||
| Stephen Boltzmann law (reminder) | ||
| Feedbacks and subsequent changes | ||
| Slide 3 |
| Slide 4 |
| Slide 5 |
| Slide 6 |
| IPCC 2007 Report on Climate |
| The recent IPCC report has clearly stated that ÒWarming of the climate system is unequivocalÓ and it is Òvery likelyÓ caused by human activities. | |
| Moreover, most of the observed changes are now simulated by climate models over the past 50 years adding confidence to future projections. | |
| IPCC report online |
| Nobel Peace Prize |
| GLOBAL Energy Flow Thru Atmosphere |
| Global Atmo Energy Balance |
| The Natural Greenhouse Effect: clear sky |
| Changing CO2 concentrations |
| Global Atmo Energy Imbalance |
| Radiative Forcing (RF)
Components {Global-average estimates and ranges; typical geographical extent and assessed level of scientific understanding} |
| Stefan-BoltzmannÕs Law (review from Lecture 5) |
| The hotter the object, the more radiation emitted. | ||
| When the temperature is doubled, the emitted energy increases by a factor of 16! | ||
| Stefan-BoltzmannÕs Law | ||
| E= (5.67x10-8 Wm-2K-4 )xT4 | ||
| E=2x2x2x2=16 | ||
| 4 times | ||
| (T is temperature in Kelvin) | ||
| 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 IN>OUT |
| Change in IR Emission to Space (contÕd) |
| AFTER GHG increase IN>OUT Eventual solution IN=OUT |
| Anthropogenically-Caused Warming |
| Initially after increasing GHG concentrations, the IR radiation to space decreases, such that | ||
| Solar in > IR out | ||
| Causing the Earth to start warming | ||
| IF GHG concentrations level off at some point, then eventually the Earth warms enough that | ||
| Solar in = IR out | ||
| ÒEventuallyÓ depends on how fast the oceans warm | ||
| The warmer Earth represents a new climate regime | ||
| With bad and good consequences that we partially understand | ||
| 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 melting of ice | ||
| Less ice reduces EarthÕs albedo | ||
| Earth absorbs more sunlight | ||
| Earth becomes warmer melting more ice | ||
| Works in the other direction as well: | ||
| Cooling makes more ice which reflects sunlight which makes Earth colder which makes more ice | ||
| =>ÕPositiveÕ 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. | |
| ÔNegativeÕ Feedback Mechanism |
| Positive and Negative Feedbacks |
| Atmosphere has a numerous checks and balances, some that counteract climate changes and some that enhance changes | |
| All feedback mechanisms operate simultaneously. | |
| The dominant effect is difficult to predict with complete certainty. | |
| Cause and effect is very challenging to prove. |
| Complexities of GHG caused Warming |
| So, as the Earth starts warming, other things start to changeÉ | ||
| The atmosphere can hold more water vapor | ||
| Water vapor is a GHG => more warming (ÔpositiveÕ feedback) | ||
| More intense precipitation events and severe weather | ||
| Land heats up faster than the oceans (remember sea breeze) | ||
| Less snowpack => earlier and smaller run-off => drier summers | ||
| Relative humidity over land will likely drop in general | ||
| Continental interiors will generally get drier? | ||
| Clouds will change????? | ||
| Having more clouds increases albedo, cooling the Earth | ||
| More clouds increase Greenhouse effect warming the Earth | ||
| Wind patterns start changing | ||
| Storm tracks and precipitation patterns change. | ||
| Winter storm tracks may move more poleward | ||
| Ice starts melting | ||
| Reducing the albedo => more warming | ||
| Continental ice melt causes sea level to rise | ||
| SVP and Temperature (from Lecture 9) |
| Claussius Clapeyron equation defines water vapor saturation vapor pressure (SVP) versus temperature | |
| SVP defines water holding capacity of air | |
| SVP nearly doubles with a 10oC warming |
| Water vapor increase at higher temperatures |
| The Natural Greenhouse Effect: clear sky |
| Upper Tropospheric Water Vapor Trends |
| Observational Evidence of Water Vapor Feedback |
| Increasing water vapor concentrations shift the altitude of water IR emission upward which DECREASES its emission (because of colder temperatures) | |
| Atmospheric temperatures have also been increasing over time (at least in theory) which should INCREASE the IR emission from water vapor | |
| To isolate the water vapor concentration change, Subtract the IR measured from water (=ÔT12Õ from HIRS) from emission measured from O2 (whose concentrations have not changed) (=ÔT2Õ from MSU) | |
| If IR from water is becoming less than emission from O2, the atmospheric water concentrations have increased => THIS IS WHAT IS OBSERVED |
| Land surface temperatures are rising faster than SSTs |
| Slide 33 |
| Snow cover and Arctic sea ice are decreasing |
| Slide 35 |
| Sea level is rising: |
| Slide 37 |
| Slide 38 |
| Surface melt on Greenland |
| Greenland ice mass budget |
| Key Points: Climate Change |
| Increasing GHG concentrations warms the Earth | |
| 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 Lectures |
| Topic - Anthropogenic Climate Change | |
| Reading - Ahrens, Ch 14: 373-400 (383-412) | |
| Problems - 14.5, 14.8, 14.10, 14.12, 14.13, 14.15, 14.16, 14.19 |