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climate:climate_change

climate change

Introduction

Greenhouse gases and global warming

the facts

  • the earth is heated by the sun which generally provides 340W/sq.m, of which around 29% is reflected back into space and the rest is absorbed by the atmosphere or earth which becomes warmer and radiates some of this back into space as infrared heat 1)
  • “greenhouse gases” in clouds and in the upper atmosphere in particular, absorb the infrared rays coming off earth and radiate some of them back to earth acting as a blanket keeping it warm
  • nitrogen and oxygen, which together account for 99 percent of the atmosphere, has essentially no influence on Earth's temperature because they did not absorb heat, but certain “greenhouse gases” do

carbon dioxide

  • earth's atmosphere is made up of around 0.04% CO2 which is thankfully low, as levels above 0.1% will cause humans and other animals to become drowsy
  • CO2 is the one of the most important greenhouse gases and is responsible for increasing our average surface temperature from minus 18°C to a livable 14°C
    • other greenhouse gases are methane and water vapor (accounts for 36-70% of greenhouse effect)
  • Natural sources of atmospheric carbon dioxide include volcanic outgassing, the combustion of organic matter, wildfires and the respiration processes of living aerobic organisms.
    • in general, the net effect is zero, for example regenerating forests will consume similar amounts of the CO2 released from wildfires, although this takes decades and may be incomplete if the forests do not flourish
    • current volcanic activity releases 130 to 230 megatonnes of carbon dioxide each year
    • there is a large natural flux of CO2 into and out of the biosphere and oceans
    • Australia remains an overall carbon sink 2) with a net effect of reducing atmospheric CO2 levels
  • Man-made sources of carbon dioxide include the burning of fossil fuels for heating, power generation and transport, as well as some industrial processes such as cement making.
    • In 2010, 9.14 gigatonnes of carbon (GtC, equivalent to 33.5 gigatonnes of CO2 or about 4.3 ppm in Earth's atmosphere) were released from fossil fuels and cement production worldwide, compared to 6.15 GtC in 1990
    • once CO2 is added to the atmosphere, it takes hundreds of years for it to be removed through natural processes
  • atmospheric concentrations of CO2 are dramatically rising, especially since 1950
    • up until 1800, it was around 250ppm, rising to around 300ppm by 1900 and 315ppm by around 1950 and then has risen sharply to around 370ppm by 2000 and to 415ppm by 2020 - arise of 50%! 3)
    • it had been mainly below 300ppm for the past 800,000 years 4)5)
    • each ppm of CO2 represents around 7.8 gigatonnes CO2
    • a small change in CO2 can have significant effects on global temperatures

methane

  • methane is 30x more potent than carbon dioxide as a greenhouse gas but has a much shorter life in the atmosphere
  • the main sources of methane release into the atmosphere are6):
    • oil and gas fields
    • large diary farms
    • some types of landfill
    • natural gas leaks from houses

global temperatures are rising

  • Overall, the global annual temperature has increased at an average rate of 0.07°C (0.13°F) per decade since 1880 and at an average rate of 0.17°C (0.31°F) per decade since 1970, and by 2015 had risen by 1°C since the 19th century 7)
climate/climate_change.txt · Last modified: 2020/01/06 22:25 by gary1