Midterm Flashcards
Milankovitch cycles
Milankovitch cycles are periodic changes in the orbital characteristics of a planet that control how much sunlight it receives, thus affecting its climate
Milankovitch thought that the temperature on Earth was influenced by 3 variables related to the position of the earth relative to the sun. If the northern hemisphere receives less energy from the sun in the summer, the ice on the North Pole will not melt and an ice age may arise.
CO2 didn’t initiate global warming from past ice ages, but it did amplify the warming. In fact, about 90% of the gobal warming followed the CO2 increase
During a volcanic eruption, a lot of ash is released into the atmosphere and blocks the sunlight
But the volcanoes emit greenhouse gas CO2 which causes the temperature to rise
There are three main orbital variations in Milankovitch cycles
Eccentricity: changes in the shape of the earth’s orbit, Obliquity: changes in the tilt of the Earth’s rotational axis and Precession: wobbles in the Earth’s rotational axis
What is Eccentricity?
The changes in the shape of the earth’s orbit
The earth does not orbit the sun in a circle, but in an ellipse shape, in which the sun is not centred. This is called eccentricity.
What is obliquity?
The changes in the tilt of the Earth’s rotational axis
Obliquity is the tilt of the Earth’s axis relative to the sun. The wider the angle of the tilt, the more the northern hemisphere turns toward the sun in summer and the more ice melts. The smaller the angle, the less ice melts and greater chance of ice age. The obliquity changes every 41,000 years
What is Precession?
The wobbles in the Earth’s rotational axis.
Precession is a toll mvoement around the earth’s axis that changes every 26, 000 ears
What is the greenhouse effect?
The greenhouse effect is the way in which heat is trapped close to earth’s surface by “greenhouse gases”.
These heat trapping gases can be thought of as a blanket wrapped around Earth
If there was no trapping of heat by greenhouse gases, our global mean temperature would be -18 celcius
Global mean temperature has gone up as greenhouse gas concentrations have gone up
For future, they have formulated a number of scenarios concering future emissions (some have reductions of greenhosue gas emissions) and have attempted to estimate what would happen under those scenarios
What are greenhouse gases?
Earth’s greenhouse gases trap heat in the atmosphere and warm the planet
The main gases are carbon dioxide, methane, nitrous oxide, water vapor and flurinated gases
IPCC Projected effects of climate change
IPCC predicts global surface temperature will continue to increase under all emissions scenarios considered
Many changes in the climate system become larger in direct relation to increasing global warming.
Continued global warming is projected to further intensity the global water cycle, including its variability.
Under scenarios with increasing CO2 emissions, the ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere
Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.
Multiple Model Approach
Our information about the earth’s climate system is limited because our climate system is so big, a computer model cannot come close to a detailed model of the Earth’s atmosphere
These models are intentionally created to have different simplifying assumptions and use different methods of modelling
The average of the outputs of an ensemble of many models is more reliable than the output of any of them
What are Robust Predictions?
If all models in the ensemble agree on something, then this is regarded as likely to be accurate. This is because if the models differ from reality in different ways, there is some hope that their errors will differ.
Climate proxies
In place of thermometer readings, climate scientists use available data that is correlated with temperature.
Tree rings, ice cores, bore holes, coral skeletal rings, fossil pollen grains, isotopes in lake and ocean sediments
Hockey Stick graph
A hockey stick graph presents the global or hemispherical mean temperature record of the past 500-2000 years as shown by quantitative climate reconstructions based on climate proxy records. A hockey stick graph is one in which the blade is near zero before the graph turns upwards to a long nearly straight increasing section
Deductive and inductive arguments
A deductively valid argument means there is no way that the conclusion could be false unless at least one of the premises is false. If the premises are all true, then the conclusion must be true.
Inductive arguments are intended to guarantee that the conclusion is true, even if all the premises are true. Any argument whose premises are all about things that have been observed in the past and whose conclusion is about the future, is an inductive argument
What is a hypothetico-deductive method?
From a hypothesis, H, deduces a prediction, O, that can be tested by observation or experiment. that is if H then O. Check to see wheher O is true, if not, reject H, if O is true, this provides support for H.
Poisson’s prediction
Poisson did a calculation that showed that, according to Fresnel’s theory, if light was projected on a disk, light would be diffracted around the edges and there would be a bright spot in the middle of the shadow. Poisson thought this was obviously wrong, and was a problem for Fresnel’s theory. Francois did the experiment and observed the spot. Fresnel won the prize
