Professor Peter Stott:

Yes. We can draw on the scientific evidence to imagine a "2° world". We have scientifically examined the measures that need to be taken to make it at least likely - a 66% chance - that we will not exceed an increase of 2 degrees Celsius on pre-industrial levels. We can see the global measures we need to take. For example, we need to reduce emissions by 50% by 2050 and to zero net emissions by approximately 2080 or towards the latter end of this century. Essentially, this means the world must put itself on a trajectory towards zero emissions and, in the grand scheme of things, in quite a short length of time, although beyond the length of time many of us expect to see, but it is the length of time our children and grandchildren could well see.

We must remember that it is the developed nations of the world that have been responsible for many of the emissions. I argue that the next question is for politicians, rather than me as a scientist; it is a question of equity in how the burden is to be shared among nations. The scientific point is that very considerable reductions need to happen to get to the 2° world mentioned in the Paris agreement. That brings us to the question of sea levels, etc. As an aside, I was born in Liverpool and have a connection with the city. The sea level is currently rising by over 3 mm a year. It should be borne in mind that because of the way climate works, "sea level" is termed as an "integrator", which means that it sums up the net effect of everything being done as a consequence of human emissions over long periods. It is not something that can be switched on and off. There is a very long-term commitment - over many centuries - to continued sea level rises as a result of the emissions we are seeing today. Sea level rises also significantly increase the risk of storm surges that have been alluded to. There is a gradually increasing sea level which is clearly attributable to human-induced emissions which result in a warming of the oceans which leads to expansion and also the melting of snow and ice on land.

The scientific community now has a very good and robust explanation and all of the terms in the equation add up. There is very strong scientific confidence in their attribution to rising sea levels. The risk to places like Liverpool and London, as mentioned, is increasing. It is a little like the way I spoke about rising temperatures and heatwaves. I refer to the curve of the background level in sea levels gradually increasing. The Thames Barrier protects London from the consequences of a storm surge, but the risk of overtopping is being increased very significantly because of a baseline rise in the sea level. Thanks to the Thames Barrier, London is currently protected, but if we consider the high levels of global warming with continued high emissions, the question of the Thames Barrier needs to be reconsidered.

Having precise numbers depends on where we look and the configuration of a particular city, the sea bed and all the rest. This is where the scientific community is ready to provide the detailed assessments. There would be differences between Liverpool, London, Dublin or wherever else we might look. I will not give precise numbers, but the scientific community is ready to advise on the matter.