Kaleab Tekle Woldemariam GISN22 Exam
You have now received an exam for GISN22 and you have 24 hours to complete the exam. Please make sure to start each question on a new page as it is different teachers that will correct your exam. Good luck. _______________________ ___________________________________ ______________________ _______________________ _____________________ ________ 1) Describe the typical patterns in the global circulation that can be used to determine where the driest and most moist places are on Earth, give some large scale (global) and small scale (regional) examples. (10 p)
The major global climate system components are the atmosphere, the hydrosphere (the ocean, rivers and lakes), the cryosphere (glaciers, sea ice and ice sheets), the land surface and the biosphere (vegetation and other living systems on land and in the ocean).However, physical processes within each component and interactions between these components are not yet well known. The sun is the source of the energy available to drive Earth’s climate system. Atmospheric circulation is driven by the uneven horizontal distribution of net incoming radiation on the earth’s surface. surface. The amount of net incoming radiation depends on latitude. Net incoming radiation is higher on the tropics, the atmosphere (and oceans) respond to this uneven distribution of radiation by attempting to move heat from the tropics and subtropics to the middle and high latitudes, where there is a net radiative loss of heat. Convection, the vertical process of heat transport, and advection, the horizontal process of heat and moisture transport, work together to accomplish this goal. Vegetation influences climate through its effects on the surface energy budget. Ecosystems affect net radiation primarily through albedo (shortwave reflectance). Most absorbed energy is released to the atmosphere as latent heat flux (evapotranspiration) and sensible heat flux. Latent heat flux cools the surface and transfers water vapor to the atmosphere, whereas sensible heat flux warms the surface air. Deserts experience large net longwave energy losses because their dry smooth surfaces and little vegetation cover leading to high surface temperatures, and limited moisture with negative feedback to support vegetation
Earth’s latitudinal atmospheric circulation is driven by driven by rising air at the equator and subsiding air at the poles. Radiative Forcing and the Coriolis effect1 produce three major cells of vertical atmospheric circulation (the Hadley, Ferrell, and Polar cells). Air warms and rises at the equator due to intense heating. After reaching the tropopause, the equatorial air moves poleward to about 30°N and S latitudes, where it descends and either returns to the equator, forming the Hadley cell, or moves poleward. Cold dense air at the poles subsides and moves toward the equator until it encounters poleward-moving air at about 60°N and S. Here the air rises and moves either poleward to replace air that has subsided at the poles (the polar cell) or moves toward the equator to form the Ferrell cell. Also shown are the horizontal patterns of atmospheric circulation consisting of the prevailing surface winds (the easterly trade winds in the tropics and the westerlies in the temperate zones). The boundaries between these zones are either low-pressure zones of rising air (the ITCZ and the polar front) or high-pressure zones of subsiding air (the subtropical high-pressure belt and the poles).
Source: Chapin III, F. S., Matson, P. A., Vitousek, P.M., 2011. Principles of Terrestrial Ecosystem Ecology, 2nd Ed., Springer Science+Business Media, LLC 2011
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Tendency, due to Earth’s rotation, of winds to be deflected to the right in the northern northern hemisphere and to the left in the southern hemisphere.
Precipitation is the major water input to most terrestrial ecosystems. Evaporation and transpiration are also other climate variables which determine whether a place will be moist or dry. In addition to global atmospheric circulation, the vegetation type also influences the amount of precipitation a place receives. In tropical rain forests where large tree canopies are common, the amount of evapotranspiration is high with correspondingly high precipitation cycled through the hydrologic cycle.
Tropical wet forests (rainforests) occur from 12°N to 3°S and correspond to the ITCZ. These forests have consistently high temperatures and high precipitation. In comparison, Subtropical deserts located at 25 – 30°N 30°N and S have a warm, dry climate because of the subsidence of air in the descending Hadley cell.
In a regional context, precipitation may be influenced by topography. A good example is the Ethiopian highlands which receive more than 1,200 mm/annum whereas the surrounding lowlands in eastern parts of the country receive on ly 100mm/annum.
2 a) Explain what is meant by the concept of "Radiative Forcing" (RF), and give the scientific units it is typically expressed in. (1p)
Radiative forcing or climate forcing is the difference between insolation (sunlight) absorbed by the Earth and energy radiated back to space. Positive radiative forcing means Earth receives more incoming energy from sunlight than it radiates to space. This net gain of energy will cause warming. Conversely, negative radiative forcing means that Earth loses more energy to space than it receives from the sun, which produces cooling. Typically, radiative forcing is quantified at the tropopause in units of watts per squa re meter (W/m2) of the Earth's surface. b) What, according to the 5th Assessment Report of the IPCC (published in 2013), have been the major contributions to radiative forcing (RF) of the climate system since 1750? Distinguish between natural and human RF, the contribution to global warming and cooling, and R F uncertainty. (3p)
The major contributions to radiative forcing (RF) of the climate system since 1750 have been GHG (Green House Gas) emissions due to indu strialization. There are two broad mechanisms for climate responses due to radiative forcing. The first mechanism is feedback through rise in the concentration of atmospheric greenhouse gases (GHGs), especially carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The second mechanism is modulating the absorption or distribution of solar energy in the atmosphere or at the land surface due to land surface changes (i.e. land use changes).
Carbon dioxide concentration in the atmosphere has increased by 37% since 1750 , exerting 1.66 W m−2 of new GHG forcing. Methane (CH4), nitrous oxide (N2O), and tropospheric O3 have increased 152%, 18%, and 36%, respectively, accounting for 0.6, 0.16, and 0.35 W m−2 of new GHG forcing2.
The natural radiative forcing come from natural processes such as volcanic activity which spews out ashes which would reduce the surface temperature by blocking sunlight reaching earth’s earth’s surface or resulting in more warming due to release of GHGs. 2
Field, C. B., Lobell,D. B., Peters, H. A. and Chiariello, N. R., Feedbacks of Terrestrial Ecosystems to Climate Change, Annu. Rev. Environ. Resour. 2007. 32:1 – 32:1 – 29 29
Figure: The contribution of human-induced and an d natural radiative forcings3. c) How does the *modelled* global average annual surface temperature compare to the *observed* global average annual surface temperature when the climate models do not include human contributions to RF? (2p)
Modelled global average annual surface temperature compared to the observed surface temperature is lesser when the contribution of anthropogenic sources to radiative forcing because greenhouse gas emissions are known to trap h eat and increase earth’s surface temperature. d) Describe the modelled spatial/geographic and seasonal variability in surface temperature and precipitation typically seen in the climate projections made by the climate models that contributed to the 5th Assessment Report of the IPCC. (3p)
The modelled surface temperature will be generally higher leading to heat waves. There will be increased variability in precipitation where dry places will be more drier and wetter places will be more wetter with increase in intensity of rainfall.
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Chapin III, F. S., Matson, P. A. , Vitousek, P.M.,2011. Principles of Terrestrial Ecosystem Ecology, 2nd Ed., Springer Science+Business Media, LLC 2011
e) Speculate as to how the modelled spatial/geographic variability in annual average surface temperature typically seen in climate projections might change if human aerosols were removed from the climate model projections. (2p)
As human aerosols are sources of GHGs, the removal of aerosols would reduce the increase in annual surface temperature.
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3 a) Give an example of a feedback loop starting with increasing air tem peratures in the Arctic. (4p)
Increasing air temperature in the arctic leadings to melting ice, instead of reflecting ice/snow , the surface absorbs and release solar radiation (becomes low albedo) triggering a feedback of further increase in air temperature. Changes in ecosystem albedo explain in part why highlatitude regions are warming more rapidly than low latitudes. As climate warms, snow, lake ice, and sea ice melt earlier in the spring, replacing a reflective snow-covered surface with a dark absorptive water body. This process, together with the resulting change in surface temperature, referred to as the snow (or ice) albedo feedback . b) Describe the impacts of changes from a human perspective – why should we care about the feedback loop you have described? (2p)
The feedback loop is likely to cause a number of climate change induced hazards such as sea level rise leading to coastal flooding, increase in surface air temperature affecting atmospheric circulation ( intensity in precipitation) and loss of habitat for polar species. However, there is an economic opportunity in terms of access to new natural resources such as petroleum and fishing grounds and new sea routes.
