Slide 1

Global warmingWhat is global warming? Why should we concern with this phenomenon?

What is greenhouse gases and how do they contribute to global warming?Theoretically.

149,597,870.7 kilometers away

Avg. Temp: 18 oC (0 oF)But the greenhouse effect keeps the earth warm

100 %25 %6 %23 + 46 %Incoming radiation = ref. from atm. + ref. from surface + abs. by atm. + abs. by earth 100 % = 25 % + 6 % + 23 % + 46 %9 %37 %9 %37 %Greenhouse effect: is the natural process by which atmospheric gases trap a major portion of the infrared radiation radiated by the Earth Greenhouse gases: are gases that are capable of absorbing and trapping infrared radiation and so warming the atmosphereEx. Water vapor, CO2, CH4, N2O (nitrous oxide), O3Enhanced greenhouse effect: the process in which atmospheric gases trap and return more than 80 % of the heat energy radiated by the EarthGlobal warming: is the increase in average global temperatures that results from an enhanced greenhouse effectGlobal warming

http://www.nps.gov/goga/naturescience/climate-change-causes.htm

Carbon dioxide to blame?Air composition: N2 (78%), O2 (21%), Ar (0.9%), CO2 (0.04%), water (variable)Svante Arrhenius (1859 1927) a Swedish scientist believed that the increase of industrialization may lead to the build up of CO2 gas in the atmosphere resulting in the increase of 5 6 oC in the average temperature of the surface of the earth. How to prove or disprove this statement using scientific methods?Greenhouse gasesMeasure the temperature and carbon dioxide concentration periodically over a long period of time (Figure 3.3, 3.8)Analysis of ice core samplesIce layers = preserved histories of the atmosphereAir bubbles trapped in ice layers provide timeline of the atmosphere history (Figure 3.4, 4.5)Deeper the ice layers, farther back in timeFrom Figure 3.5, beginning at around 1800, CO2 began accumulating in the atmosphere at an ever-increasing rate, corresponding to the beginning of the Industrial revolution and the accompanying combustion of fossil fuels that powered that transformationGreenhouse gases (contd)Air composition: N2 (78 %), O2 (21 %), other (1 %)Other (1%): includes but not limited to CO2, H2O, CH4 (greenhouse gases)Why N2 and O2 are not greenhouse gases?Molecular shapes and vibrationsBut first, consider the molecular shapesRemember Lewis structure?Determine the valence electrons for each atomEx. CH4 C: 4 1 = 4 Ve- H: 1 1 = 1 Ve- 8 Ve-Arrange electrons in pairs to satisfy the octet rule

or

Since opposite attracts and like charges repel, assume the most stable molecular shape has the bonding electron pairs (and non bonding electron pairs) as far apart as possible

More on the shape of molecules

104.5 oBentH2OTrigonal pyramidalAmmonia, NH3109.5 oTetrahedralMethane, CH4Vibrating molecules and the greenhouse effectHow does the greenhouse gases trap heat?Molecules respond to photons of energy

Increasing energySome radiations contain enough energy to break a bond, but IR radiations can only promote vibrations in a molecule11Vibrational modes for CO2

(a), (b) stretching vibration; (c), (d) bending vibrationsWhen energy is absorbed by a CO2 molecule, it can eitherGet excited and collide with other atmospheric molecules to transfer extra heat orReemit the extra energy directly also as heatAny molecules that can absorb IR radiation can act as a greenhouse gasN2 and O2 are not greenhouse gases because they are diatomic molecules that energy generated through vibrations are canceled outHomework Read Chapter 3