CLIMATE CHANGE

THE GREAT DEBATESession 9

BIOLOGICAL FACTORS

• Changes in albedo. Surfaces vary in the degree to which they absorb or reflect solar energy

• Changes in particle concentrations in the atmosphere

• Changes in concentrations of greenhouse gases in the atmosphere

They are capable of changing the climateof our planet in three different ways:

CHANGES IN ALBEDO

• Some surfaces such as glacial ice, snow, bare sand and light-coloured rocks reflect a lot of solar radiation. They are said to have a high albedo and appear light in digital images

• Other surfaces such as smooth water surfaces and vegetated surfaces absorb a lot of solar radiation. They have a low albedo and appear dark in digital images

Albedos vary between different kinds of surfaces. Vegetated surfaces have low albedos

ATMOSPHERIC PARTICLES

• Naturally occurring particles consist of dust, soot, pollen grains, spores and tiny salt crystals. They play a role in cloud formation

• Light-coloured particles reflect solar energy while dark particles absorb it

• Some volcanic eruptions produce large quantities of volcanic ash and cause world-wide cooling for up to five years

GREENHOUSE GASES

• They are efficient at trapping some of the long-wave (infrared) radiation that is radiated by the Earth

• Some of these are present naturally such as water vapour, carbon dioxide and methane

• Others do not occur naturally but are produced by industrial processes

CYANOBACTERIA• These unicellular organisms were

capable of carrying out photosynthesis using carbon dioxide from the atmosphere and producing oxygen as a waste product

• Over many hundreds of millions of years they changed the Earth’s atmosphere from one dominated by greenhouse gases to one dominated by oxygen and nitrogen

ROLE OF PLANTS

• Plants continued the work begun by cyanobacteria to raise oxygen levels to a level where multicellular animals could develop

• By invading the land they reduced the albedo of large areas of the Earth’s surface allowing more solar energy to be absorbed. This undoubtedly had a climatic effect

EFFECTS OF HUMANS

• They changed the albedo of large areas of the earth’s surface by vegetation clearing, creation of reservoirs, irrigation agriculture and urban development

• Some of the changes caused an increase in albedo while others caused a decrease

• The balance between the two is not clear

Centre-pivot irrigation agriculture in SaudiArabian desert has reduced albedo

Large scale urbanization around Tokyo Bay in Japan has increased albido

EFFECTS OF HUMANS• Human activities increase the

concentrations of dust and soot. Dust particles are produced by industrial activities while soot is generated by fuel burning and fires.

• Dust particles have a cooling effect because they scatter and reflect while soot particles tend to absorb solar energy

• All particles tend to act as nuclei for cloud formation and precipitation

EFFECTS OF HUMANS

• Human activities have increased dramatically the concentrations of naturally occurring greenhouse gases such as carbon dioxide and methane

• Other greenhouse gases have been introduced by industrial activities such as nitrous oxide, ozone, chloro-fluorocarbons and nitrogen trifluoride

Graph shows rapid increase in CO2 concentrations in last fifty years. Seasonal fluctuations are due plantactivity in the Northern Hemisphere

Increase in methane has slowed since 1990. It is avery powerful greenhouse gas but is present in much lower concentrations than CO2

INCREASE IN CONCENTRATIONSOF GREENHOUSE GASES

• Since the industrial revolution began carbon dioxide concentrations have risen from 270 to 390 ppm(v) and methane concentrations have risen from 700 to 1820 ppb(v)

• Carbon dioxide is derived mainly from the burning of fossil fuels while methane is produced from a number of sources

URBAN CLIMATES (1)

• Local climates in urban areas have changed significantly

• Every effort is made to dispose of precipitation as rapidly as possible

• In rural areas enough moisture remains in the environment to keep temperatures down by evaporation but in urban areas that is not the case so higher temperatures can be expected

URBAN CLIMATES (2)

• Urban areas generate large amounts of heat through industrial processes, transport, heating and air conditioning

• Most cities have also grown rapidly in size during the last 100 years

• Most long term climate records are from cities but because of the rapid increase in energy output it is not surprising that they show a temperature increase over time

Upward temperature trend at New York should not be regarded as evidence of global warming becauseof an increase in locally generated energy input