GPHY 314 Quiz: Week 5

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29 Dec 2020
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WEEK 5: Modern Climate Change and Future Predictions
Summary to Date
Class began with Earth’s radiative balance between energy in and out, imbalances
Then discussed how climate has changed over Earth’s history
o GHGs were implicated/correlated with changes at all timescales
Global climate change: modification of mean or distributional characteristics of global climate
for specified period
o Can be due to natural or anthropogenic processes
Extended periods of global climate change requires radiative imbalance
Just saw evidence for modern warming
o Modern warming rate greater than recent past, concurrent with massive rise in GHGs
o Compare carbon dioxide measurements over past 2,000 years
Currently around 410 in 2019, compared to 280 in over last 2,000 years
Consistent picture of extreme change
o Looking back at 800,000 years, no period where carbon dioxide raised about
300ppm, which was even then only for a very short period
Very unprecedented then, and if we look at last 3.3 million years, our
modern levels are really only comparable to those 3 million years ago
If we continue at the current rates of emissions, there will be more
carbon dioxide in Earth’s atmosphere by 2025 than at any time in at
least the last 3.3 million years (de la Vega et al., 2020)
Sea levels 20 metres high, global temperatures 2-3°C higher so it
gives us a sense of what we may see if we continue at these rates
o Takes 50,000 to 100,000 years for current amounts of carbon dioxide in atmosphere to be
pumped out, so it will take at least this long for current levels to be restored to normal
Simple correlation suggests GHGs may be the cause of modern warming
o Generate estimate of global radiative forcing from carbon dioxide
o As you increase amount of GHGs, get fairly dramatic increase in global temperature
o Comparing the two, there’s a strong statistical association/fit between the two
o Can know this by looking at history of carbon dioxide science, attribution and detection
History of Carbon Dioxide Science
In 1827, Joseph Fourier (French mathematician and physicist) wondered why Earth’s average
temperature approximately 15°C when his calculations indicated should be much colder (-18°C)
John Tyndall (Irish scientist, fascinated by growth and formulation of glaciers) began series of
experiments to measure amount of infrared radiation that certain gases could absorb and transmit
o Tyndall found that water vapor and carbon dioxide were good absorbers and emitters of
infrared radiation
Eunice Foote (1856) made presentation of series of experiments where she described it seemed
that certain gases absorbed the sun’s rays better than others
o Incorrect, but did highlight important of water vapour and carbon dioxide for potentially
leading to heating with some interaction with heating
o First person to suppose what this means for global climate i.e. increase in temperature
Arrhenius first estimate that role carbon dioxide could play for warming on earth
o First instance it was supposed small changes in atmosphere could play larger role in
Earth’s climate
Angstrom’s [faulty] reasoning ignored higher in atmosphere you have potentially less thick
atmosphere and less carbon dioxide, so warming could still occur
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Callendar generated some of the first global temperature estimates, linked to his guesses about
how carbon dioxide was increasing
o Suggested as warming of ocean layer occurs, it would actually reduce the amount of
carbon dioxide
Prevailing belief back then was that ocean would absorb extra carbon dioxide
Not until 1950s that we got different, better understanding of warming properties
US Air Force needed to understand atmosphere during Cold War for communications and heat-
seeking missiles
o New missiles couldn’t see very far if they used wavelength that carbon dioxide absorbed
Nimbus-3 experiment (1969) between observed and theoretical measures
o Satellite observation used advanced spectrometer over Gulf of Mexico that was able to
generate an understanding of how atmosphere emitted radiation
o Comparison shows understanding of physics and absorption of carbon dioxide matches
Jason Report (1979) not from field of climate science, asked to look at whether carbon dioxide
could lead to future warming
o Final conclusion if you increase carbon dioxide, alters radiative properties of atmosphere
Later National Academy of Sciences report (1982) also looked at this issue
o Concluded if carbon dioxide continues to increase, negligible climate changes will result
o Potentially catastrophic events to be considered -> If Antarctic ice sheet melts, could case
rise in seal level by 5 metres, which would cause flooding on most of the US East Cost,
including Florida and Washington
o Unanimous agreement that temperature increase of ±1.5°C will bring significant changes
to climate, including rainfall distribution and alterations in biosphere
1980s first comprehensive assessments of global temperature records with climate modelling to
bridge understanding of how carbon dioxide could impact climate
James Hansen TedTalk video
o Energy policies continued to focus on fossil fuels gave public talk criticizing lack of
appropriate energy policy in 2004 and 2005
o Led to calls from White House and NASA Headquarters, saying he couldn’t give talks or
speak to media without approval
o Adding carbon dioxide reduces heat radiation to space so there’s a temporary imbalance
until earth warms up enough to again radiate into space the amount of energy coming in
o Upper half of ocean gaining heat at substantial rate, deep ocean at smaller rate, and
energy is going into net melting of ice all over
o Total imbalance now is 0.6 W/m2, which is ~x20 greater than rate of energy used by all
of humanity
o If want to stabilize climate, need to reduce carbon dioxide 391ppm back to 350ppm
o Major imbalance occurred when there was a solar minimum, disputing those who argue
that the sun is the reason for warming
o Climate history for global temperature, carbon dioxide, and sea level over 800,000 years
High correlation between all three
Temperature changes slightly lead carbon dioxide by a few centuries
Climate change disputers try to use this lag to say temperature influences carbon
dioxide, not the other way around
But lag expected because small changes in Earth’s orbit alter distribution of
sunlight on earth
o Both Greenland and Antarctic Ice Sheet both losing mass, several hundred cubic
kilometers per year (at accelerating rates)
o Last time carbon dioxide was at this level, sea level was ~50 meters higher
o Monarch butterfly could be 20-30% of animals made extinct due to this
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