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Week2 multi-choice answers

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).

Question 1: 

Water vapour is the dominant source of the greenhouse effect in the Earth's atmosphere. It is the reason why the Earth is not at -18 degrees C. The contribution of other greenhouse gases is to an enhanced greenhouse effect, but there impact is much smaller than the 30 degrees that water vapour gives.

Question 2:

a & c are correct. The last three decades have all been warmer on average than any since the 1850's, while warming over the last decade has been consistent with zero. Note that the meaning of "consistent with zero" does not mean that the value is zero, but rather than the error associated with the measured warming overlaps with zero. In the case of the recent IPCC report the range of -0.05 to 0.15 degrees per decade crosses the zero line, and so is consistent with zero.

Question 3:

b - very likely. This is a conclusion drawn directly from the IPCC reading.

Question 4:

b - in the ocean. The ocean has a very high specific heat capcity (i.e. it can soak up a lot of energy with only modest warming). This is where a lot of the energy from recent warming has gone, and indeed is suggested as one of the reasons that recent temperature changes have been towards the lower end of the model predictions.

Question 5:

c & d. Negative radiative forcing causes the planet to cool, or means that more energy is going out from the top of the troposphere than is coming in. In this case aerosols or volcanic activity act to block incoming solar radiation and so create an imbalance which acts to cool the planet.

Question 6:

b - Clouds are extremely difficult to model and understand, and remain a significant cause of uncertainty in the climate system.

Question 7: 

c - The IPCC believe it is extremely likely that at least 50% of the warming has been caused by human activity.

Question 8:

d - The models show a wide range of warming depending on the scenarios which are adopted. However, all of these show at least 1.5 degrees of warming.

Question 9: 

abcd - All of these statements are correct. In fact they are a set of statements that are often used by skeptics to argue for the non-reality (or non-importance) of global warming. However, most of them have relatively little impact on the key questions of today, and you might find it a useful exercise to deconstruct them as skeptical arguments. (P.S. I am aware this could look like a trick question, so everybody has got the marks for it).

Question 10:

c - The figures in the IPCC report show that sea level rise has been approximately 150 mm.