Week 1 of the course has already thrown up a variety of questions, so here goes with some answers…

1. What is the process of ice sheet sublimation? We’re all familiar with evaporation, where a liquid turns into a gas – e.g. liquid water turning into water vapour (a gas). Sublimation is when the molecules in a solid (in this case, ice) go straight into the gas phase (water vapour), without turning into liquid first.

2. Does increased snow/ice melt due to climate change and a warmer world lead to more precipitation as snow? Not really. More snow/ice melt produces more liquid water, much of which ends up in the ocean, from where it can be evaporated and then return to the land as precipitation. Overall we observe more evaporation and precipitation in a warming world (the hydrolgogical cycle ‘spins’ faster). But because it is getting warmer more of that precipitaiton tends to be rain rather than snow.

3. How did the process of advancing/retreating ice start? Sea ice (for example) tends to expand in winter during the polar night (darkness). In the spring and into summer as the days get longer, this tends to melt more ice. That in turn triggers the ‘ice-albedo positive feedback’, absorbing more sunlight and accelerating the ice melt. On a much longer timescale we can think about similar processes governing the creation and melt of giant ice sheets on land. More on all this next week.

4. How is atmospheric circulation driven by release of latent heat? Atmospheric circulation is driven, in general, by the different amounts of heating of different parts of the atmosphere. Most importantly, more sunlight is absorbed at the equator than the poles, and that drives an atmospheric circulation that tends to redistribute heat towards the poles. In addition, when water condenses in the atmosphere (such as when clouds form), this releases latent heat. That tends to cause the air to expand and rise upwards, starting the process of convection (a kind of atmospheric circulation). On small scales this is what creates the remarkable tower like structures of clouds. On larger scales the release of latent heat in monsoonal rains (e.g. in India) fuels an upward flow of the air over land, sucking in air from over the ocean, which returns at height in the atmosphere – this is the monsoon circulation.

5. Can we stabilise climate and emissions whilst population and consumption increases? Only if the consumption is no longer of fossil fuels, or meat eating, or any of the other processes that produce emissions of ‘greenhouse’ gases. More on this in the coming weeks.

6. Who is going to support the investments required globally to prevent the acceleration of climate change? This requires a change in our economic system so that there is a price on the pollutants that are accelerating climate change and a corresonding reward for technologies that can provide energy and other services without contributing to climate change. On a national scale, e.g. in Germany, there have been some success stories with governance arrangements that have incentivised the solar energy industry and are helping it gain market share over fossil fuel burning. Globally there are some signs that solar energy is taking off, but the overall picture is not good. More on this in the coming weeks.

Professor Tim