Thank you for answering the multi-choice questions for week 2. The answers and some feedback are below. Your marks will also be available shortly. Don't worry if your mark isn't very high (this counts for a tiny fraction of the module).
Volcannoes will pump aerosols into the atmosphere and will hence block incoming solar radiation. They are the only one of the items that will create cooling, the others are all greenhouse gases.
Temperature and the availability of water are the two crucial variables involved in the use of tree rings for temperature measurements. The other elements can certainly create effects, but are less important.
Only decreasing the albedo of the Earth will result in an increase in the equilibrium temperature. Decreasing the solar activity results in less incoming radiation, and acts to cool the planet. Increasing the albedo would reflect more light, and so cool the planet. Increasing water vapour in the atmosphere will result in the temperature increasing, but this is due to the greenhouse effect and so the equilibirum temperature (as derived in the lecture) will not be affected since it doesn't include greenhouse gases. However, decreasing the albedo will result in more solar radiation being absorbed, and will act to increase the temperature.
b - The differing weights of 18O and 16O means differing rates of evaporation and condensation which in turn creates different ratios of 18O to 16O at different temperature locations around the world.
c - The main driving force for ice ages is not to do with the average distance between the Earth and sun, but the solar forcing. This is dominated more by the angle that incident light makes with the surface of the Earth than the distance.
All of these statements are actually true. I am aware that this could be regarded as a trick question and so your total is out of 8 rather than 9 (i.e you haven't been penalised for getting it wrong).
b and c are correct.
acd are correct. The only incorrect statement is that sea levels have never been higher. In practice there are epochs in geological history when there has been even less ice than today.
b and c are correct.