climate change

  • the temperature of planet Earth over time → graph where the 0 line represents the average temperature from 1960-1990, used to compare temperatures to what we think it was in the past
    • temperature isn’t static, the Earth was warmer hundreds of millions of years ago, though now we see rapid warming
    • Earth was undergoing a slight cooling until the Industrial Revolution when humans started burning fossil fuels
  • natural forcing mechanisms for climate change → solar output (luminosity), continental drift and climate, thermohaline circulation, distance/angles between the Earth and sun, and changes in atmospheric composition
  • solar output (luminosity) → 11 and 22-year cycles of fluctuating irradiance; 40-50 years of reliable messurement suggests a potential increase of approx. 0.09 watts during periods of maximum luminosity (compared to 0.4 watts from GHGs)
    • luminosity is not a significant factor in the rapid warming of the last 100-200 years (may increase changes over wide periods of time)
  • continental drift and climate → ocean currents change in response to continental movement, changing how the ocean transports warm and cold water
    • when equatorial ocean currents circulate - earth is warmer
    • equatorial ocean currents are blocked - high-latitude currents will isolate the polar continent, causing polar temperatures to drop
    • a supercontinent (i.e. Pangea) would have likely led to a warmer climate due to more EMR being absorbed by a land mass causing change in precipitation patterns
    • continental drift and climate is not a significant factor as there has been no supercontinent at the equator in past 100-200 years, though may explain temperature differences in millions of years
  • deep ocean/thermohaline circulation → warming after the last ice age caused large amount of freshwater to be released into the ocean, slowing the ocean circulation which causes strong cooling over the North Atlantic for 600-1000 years (the young dryas period)
    • often called the Little Ice Age, though this long-term cooling trend was interrupted by rapid warming of the past 150 years
    • not a significant factor, slowing ocean circulation may be a negative feedback globally (cooling down of temperatures), and may contribute to significant regional variation due to melting ice, but more data it needed
  • distance/angles between the Earth and sun → distance and angle between the Earth and sun has varied, the sun changes in energy output and the Earth’s orbit brings it closer to and farther away from the sun in a predictable cycle
    • the Earth’s elliptical orbit can stretch and contract over time, changes in the tile of the Earth can occur
  • Milankovitch cycles → changes the duration and intensity of sunlight reaching the Earth, 3 distinct cycles in how the Earth rotates around the sun, variation in these 3 cycles are believed to be the cause of Earth’s ice ages (glacials)
    • not relevant to the warming of the past 200 years
  • changes in atmospheric composition → the strongest candidate to explain overall patterns in Earth climate that can account for the changes of the last 100-200 years
  • understanding the 0.8℃ warming of the last 150yrs → not the warmest period ever in Earth’s history, but unique in that it cannot be explained by any natural forcing mechanisms as we currently understand them
  • causes of global climate changes → greenhouse gases explain warming trends, allows the penetration of visible and traps infrared radiation, a significant portion of which stays trapped on Earth and warms the atmosphere
    • the concentration of greenhouse gases are increasing and infrared radiation produces almost double the warming that visible light does
  • radiative forcing → the imbalance in the Earth’s energy budget that results when the amount of energy radiated to outer space is changed through either natural or human influences
  • positive radiative forcing → results in warming; factors include GHGs, CFCs, nitrous oxide, tropospheric ozone, black carbon, sun, volcanic aerosols
  • negative radiative forcing → results in cooling, natural mechanism can cool the climate; factors include stratospheric ozone, reflective aerosols, soil dust, cloud changes, changes in land use, volcanic aerosols
  • cooling the atmosphere → some pollutants and atmospheric aerosols can cool the atmosphere as they reflect sunlight back into space, preventing the transmission of radiation into the atmosphere
    • example - volcanic eruption produce a sulphur haze into the atmosphere that can cause this form of cooling
  • causes of the enhanced greenhouse effect → the amount of gas emitted and properties of the gas
  • average residence time → the length of time gas resides int he atmosphere
  • global warming potential → how much given mass of greenhouse gas contributed to global warming over a period of time compared to the same mass of carbon dioxide
  • causes of the enhanced greenhouse effect → average residence time and global warming potential
  • average residence time → the length of time gas resides in the atmosphere
  • global warming potential → how much given mass of greenhouse gas contributed to global warming over a period of time compared to the same mass of carbon dioxide
    • CO2’s global warming potential isn’t the highest, but there is a lot lower concentration of these materials in the atmosphere so they won’t warm the earth as much
    • CO2 also has a higher radiative forcing
  • 5 significant pools in the carbon cycle → atmosphere, forests and soils, surface ocean, deep ocean, fossil fuel
    • interested in the movement of carbon in and out of these pools
  • carbon fluxes → photosynthesis/respiration, changing land use (deforestation, forest regrowth), surface ocean flux (oxygen from the atmosphere gets dissolved), flux to the deep ocean (carbon from the surface moves to the deep ocean), fossil fuel
  • terrestrial photosynthesis → fossil fuels account for more than 2x the carbon currently stored in forests and soils, not able to absorb all the fossil fuels as even if we could double forested areas to absorb 4280 GT, we would still have excess CO2 to dispose of eventually
  • increased ocean uptake → even if the oceans could absorb more CO2, this option is limited by the rate at which it moves out of the shallow oceans into marine organisms and deep oceans
    • the dissolution of CO2 in oceans makes them more acidic, endangering coral reefs and any organisms with a calcium-based shell
  • International Panel on Climate Change (IPCC) → the leading international body for the assessment of climate change, est. 1988 with the purpose of providing a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts
  • 1.5℃ global warming → the increase in the Earth’s average temperature from the baseline average temperature (1960-90), enough heat and energy to tip many important natural systems past a dangerous turning point
  • potential impacts of going from 1.5℃-2℃ → billions more people will experience severe heatwaves, seas rise another 10cm, climate-related risks and poverty, coral reefs could decline up to 99%, the global fishery could decline, impacts on developing economies
  • changes in the Arctic and Antarctica → polar amplification is exacerbated by feedback mechanisms: the release of methane and CO2 stored in permafrost, and melting of ice and snow will raise sea levels and decrease the salinity of the ocean
  • impact on polar bear populations → they rely on ice to help it hunt further into the ocean, and the melting causes more polar bears to be on coastlines and unstable hunting
  • ecological effects → affects every species on earth, some will expand their range and thrive; the greatest risks are polar seas, coral reefs, mountain ecosystems, coastal wetlands, and tundra
  • dealing with global climate change → focus must be CO2, two methods are mitigation and adaptation
  • mitigation → moderating/postponing global climate change, i.e. buying time: reducing CO2 emissions through developing fuel alternatives and increasing energy efficiency; planting and maintaining trees to increase photosynthesis
    • geo-engineering and climate engineering → large-scale engineering and manipulation of the planetary environment to combat/counteract anthropogenic changes in atmospheric chemistry
    • CO2 management → separate and capture, sequester from the atmosphere, artificial ocean upwelling, ocean iron fertilization, ocean alkalinization
    • solar radiation management → reduce the amount of solar radiation reaching the earth, i.e. spraying millions of tonnes of reflective particles of sulphur dioxide, mimics volcanic eruptions
  • adaptation → responding to changes, implies that climate change is unavoidable