1. Understanding Earth’s energy balance is essential to understanding the issue of global warming. For example, the solar energy striking Earth’s surface averages 168 watts per square meter (W/m2), but the energy leaving Earth’s surface averages 390 W/m2. Why isn’t Earth cooling rapidly?
The Earth’s energy balance
From the picture above, the incoming solar radiation (342 W/m2) is equal to the total outgoing radiation [reflected solar radiation (107 W/m2) + Outgoing longwave IR radiation (235 W/m2)] = 342 W/m2 (outgoing radiation going to space).
At the Earth’s surface, input [absorbed by surface (168 W/m2) + LWIR reabsorbed by surface (324 w/m2) = conduction (24 W/m2) + loss of heat by evaporation (78 W/m2) + surface emission (390 W/m2)] both total input and output equals to 492 W/m2….
Both the upper atmosphere and Earth’s surface energies are balanced. Therefore the Earth as a whole isn’t heating or cooling.
However, at the earth surface or ground troposhere level, the greenhouse effect comes into play in regulating the earth surface temperature by trapping the heat and reradiate it to the earth surface. As we go from the troposphere to stratosphere, the temperature will decrease as it is further away from the earth surface.
Earth absorbs longwave UV and visible rays and emit IR radiation.
- Nitrogen, oxygen, and argon absorb and emit little or no radiation.
- Water vapor, carbon dioxide, ozone, methane, and nitrous oxides all absorb some wavelengths of longwave IR radiation. Because they absorb longwave IR, they also are capable of emitting longwave IR.
- Water vapor absorbs some shorter wavelengths of IR radiation, and ozone absorbs UV radiation, but gases in the atmosphere absorb no visible light.
- Clouds absorb all longwave IR radiation well (and hence are capable of emitting longwave IR well). They also reflect visible light well (they have a high albedo).
The above substances trap and reemit IR radiation back to the surface of the earth.
The continual increasing emission of greenhouse gases occurring at the troposphere of the earth will disturb the stability of Earth’s Energy Balance and the resulting energy imbalance warms our planet by either Greenhouse effect and enhanced greenhouse effect caused by humans.
2. Do you think the statement made by the cartoon is justified? Explain.
The statement in the cartoon is unjustified as global warming is capable of causing climate change like excessive snowfalls in certain areas of the world. This appears to be counter-intuitive at the first glance but can actually be proven by the precipitation cycle.
In global warming, the average global temperature is generally increasing as time passes. As the climate warms, evaporation increases from water bodies such as oceans and this increases the proportion of water vapor in the air, resulting in an increase in humidity. The increase in moisture in the air is then expected to result in an increase in precipitation as the amount of snowfall is actually dependent on the amount of moisture present in humid air. This means that larger storms can be driven and this then results in the heavier snowfall as per the observation.
In addition, snowstorms can occur if temperatures are in the range of -10°C to 0°C. Global warming decreases the probability of snowstorms occurring in the Southern regions where it is generally warmer. However, in northern regions where it is actually colder, the temperatures are often too cold for very heavy snow and warming will actually result in conditions that are more favorable for snowstorms to occur. (Kunkel et al., 2008)
3. One of the first radar devices developed during World War II used microwave radiation of a specific wave range that triggers the rotation of water molecules.
Why was the design not successful?
Water is actually an excellent radar reflector. Both rain and waves can reflect radar energy back and create images on the screen, blanking out entire regions.
Absorption of microwave radiation by water in the atmosphere interferes with the detection of intended objects. Water vapour and weather conditions would have affect the operationability of the radar. The conventional radar device which is first being implemented also did not cover a large range.
Doppler weather effects (precipitation) were found to degrade conventional radar and moving target indicator radar, which can mask aircraft reflections. Doppler effects degrade performance of systems not designed to account for moving objects. Fast-moving objects cause a phase-shift on the transmit pulse that can produce signal cancellation.
Conventional radars are effective in measuring precipitation through echoes and reflectivity, but are not as accurate in storm detection as the Doppler radar. The Doppler radar measures speed and direction rather than the intensity of a signal by using the principle of the Doppler shift.
Doppler radars are created to replace conventional radars. Modern weather radars are mostly Pulse-Doppler radars.
Some military radars uses the reflection, absorption and scattering of light instead of echoing sound waves. LIDAR (light detection and ranging) can be used for weather, detection of greenhouse gases, aerosols, atmospheric pollutants.
4. Now that you have studied air quality (Unit 1), Stratographic ozone depletion (Unit 2), and global warming (Unit 3), which do you believe poses the most serious problem for you in the short run? In the long run?
Short run – Air Quality
Air quality at the troposphere, the harmful air particles and gases poses the most serious problem in the short run as it has a direct effect on humans and some can cause harmful or irritation effect on short term exposure and cause disease in long term exposure to polluted gas.
Long run – Global Warming
Global warming causes sea level to rise due to melting of permafrost. There is a large population of people living in countries near the seas and deltas etc (e.g. Shanghai). The rise in sea level can flood a large area of land and many will have to evacuate. Also, there is not enough effort done to slow down or reverse global warming.
San Francisco State University, Department of Geosciences, Earth’s Long-Term, Global Average Energy Budget http://funnel.sfsu.edu/courses/metr104/S12/handouts/TQ_EarthsEnergyBudget.soln.html
Kunkel, et al. GEOPHYSICAL RESEARCH LETTERS, Heavy precipitation associated with tropical cyclones. vol (37), 2010