wk 2: climate change

weather vs climate

• weather

  • current state of atmosphere with respect to temperature, precipitation, wind, and sky cover

• climate

  • statistical description (average and variability) of the weather at a location over longer periods of time (typically 30 years)

climate change

• significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years

changes in global surface temperature

• each of the last three decades has been successively warmer at the earths surface than any preceding decade since 1850

• in north hemisphere 1983-2012 was likely the warmest 30 year period of the last 1400 years

• its getting warmer, and its getting warmer faster

• 10 warmest years have now all occurred since 2005

• 2019 ranks as earth’s second warmest year since 1880

• 2020 also was one of the hottest years

cryospheric changes

• over last two decades Greenland and Antartica ice sheets have been losing mass

• glaciers continued to shrink almost world-wide

• arctic sea ice and northern hemisphere spring snow cover have continued to decrease in extent

our energy source: the sun

• centre of sun, pressure is so great that the hydrogen atoms squeeze together and form helium

• process that causes this: nuclear fusion

  • releases massive amount of energy → is what makes sun so hot → hit the earth/other planets

radiation and energy flows—no atmosphere

• energy from sun drops to 342 watts/m2 once reaches earth

• what happens to this energy at earths surface?

• look at situation with no atmosphere

• earth’s surface will absorb parts of solar radiation → starts to heat up → as it heats up will emit radiation of its own → gets hotter and hotter → eventually will emit the same amount of energy it absorbs

  • reaches equilibrium

• earth’s surface temp w/o atmosphere: -18 C

radiation and energy flows—with atmosphere

• same 342 w/m2

• radiation starts to pass through atmosphere

• only about 10% of the emitted infrared radiation gets through the atmosphere, most of it is absorbed in atmosphere trace gases

  • selective absorbers

  • water vapour, carbon dioxide, methane

• atmosphere also warms up (bc absorbing) and emits energy

  • part of emitted energy goes back to surface, some of it emits back to space

• earth’s surface absorbs more energy than it emits

• (fluxes) thermals and evaporation make up the difference, balance out energy fluxes at earth’s surface

radiation and energy flows—greenhouse effect

• global average without atmosphere: -18

• global average with atmosphere: +15

• natural greenhouse effect: +33

• water molecules will stay in atmosphere for 10 days

  • rain flushes it out to come down to earth, form clouds, etc

  • co2 + methane can stay in atmosphere for 100 years

  • bc natural speed of carbon cycle is a lot longer compared to water cycle

• KEY IDEA: having an atmosphere changing affects what happens to the energy emitted from the sun, determines how warm it is at the surface

forcing the climate system: natural/anthropogenic

• 3 main ways for changing energy fluxes that can result in different surface temp.

  1. change incoming energy from the sun: change in earth’s orbit

  2. altering concentration of greenhouse gases + aerosols: co2affect how much energy is trapped, and reradiated (does not go to space) back to earth surface

  3. alter characteristic of earth’s surface: change how much radiation is reflected, how much energy is used to evaporate water, how hot the surface needs to be to emit necessary infrared radiation

• all changes can have natural or anthropogenic causes

greenhouse gases: co2

• co2 occurs naturally as a trace gas in atmosphere

• concentration is determined by carbon cycle, carbon cycle has fast part (driven by photosynthesis) and slow parts (geological processes)

• how much co2 is in the atmosphere?

• Mauna Loa observatory measuring since 1958

  • curve is shooting up

  • July 2020 co2 concentration 414 parts per million (ppm)

  • 48% higher than natural levels prior to Industrial Revolution

• primary source of new co2 is linked to human activity (burning fossil fuels, deforestation)

• no equivalent natural process that can rid co2 out of atmosphere at equally fast rate

  • co2 just keeps accumulating in atmosphere, in oceans

  • when in oceans → acidification

• comparing to pre industrial times

• concentration of co2 currently is way outside the natural range over the last 800 thousand years

volcanic eruptions: aerosols

• big volcanic eruptions can spew tons of aerosol concentrations that cool the atmosphere

• washed out of atmosphere fairly quickly by rain

land use changes

• changing forests to fields or cities completely changes how surface interacts with radiation

• the darker and drier the surface, the more energy it will absorb and turn into heat