 The carbon cycle is very simple, it's about the cycling of carbon through natural systems, through plants, through soils, through the ocean and back out into the atmosphere. In the natural carbon cycle there's a lot of fluxes of carbon dioxide, so carbon goes in and out of the ocean, in and out of the terrestrial biosphere every year. The carbon is constantly flowing between these different systems and large amounts of carbon moves all the time. I mean in the terrestrial biosphere and the trees and the forests it's very easy to see. If you live in a place that has a forest area with seasons, you see in the winter the trees they have no leaves and the spring comes and the leaves build up. This is all good carbon dioxide that goes in the leaves and in the fall, in the autumn when the leaves fall down then the carbon is emitted back in the atmosphere. So you have a huge signal there of CO2 going in and out of the atmosphere. So the ocean will take up CO2, it dissolves in the surface of the ocean and also the ocean will release CO2 to the atmosphere and that depends on the concentration of CO2 in the atmosphere and the concentration of CO2 in the ocean and they form a balance with each other. So there's a continuous massive exchange of carbon dioxide between the atmosphere and the land and the atmosphere in the ocean that is roughly in balance until we introduce human change. So the experiment that we're inadvertently perhaps conducting with the climate system is to move huge volumes of carbon from these stores undergrounds in the form of fossil fuels and bringing it to the surface and burning them and adding this carbon to the atmosphere. What we're doing now is putting everything out of balance so we're adding carbon to the atmosphere. It's new carbon, it's not part of the natural cycle, it's one that we've dug out of the fossil reservoir where they were stored and we've put them back in the atmosphere. This is new carbon and it puts the system out of balance. Although the human emissions are much smaller than the natural fluxes, the natural fluxes approximately are in balance and so they're not causing a net increase of carbon dioxide in the atmosphere. The human emissions, however, are very rapid and the natural systems don't have time to respond to them and so you get a net imbalance of raised carbon dioxide concentrations in the atmosphere. It's unequivocal that the amount of carbon dioxide in the atmosphere is increasing and is increasing faster and is increasing faster than ever. The rate of change now is incredibly rapid and what's more it's pushed us outside of the bounds of what we've seen in terms of atmospheric concentration throughout the ice ages. We have not had levels of CO2 at 400 parts per million by volume in 800,000 years of history. In the Earth's past throughout, in and out of the ice ages, the concentration of CO2 in the atmosphere ranged between about 180 parts per million, 280 parts per million and it took thousands of years for it to change between those states. This is now, it's gone up to 350 and even top in 400 parts per million on a single day basis and that's happened over a period of a couple of hundred years. Every single generation is emitting more than the previous generation because I mean the emission of CO2 increasing exponentially and we emitted so far if you start from the beginning which is like the industrial revolution in 1750 or something when we started slowly I mean to burn fossil fuel and from that time up to today we emitted something like 2000 gigaton of CO2. More than half of this has been emitted over the last 50 years. And we know where that CO2 is coming from because we do the isotopes of the carbon we know it's coming from fossil fuels. So carbon is increasing in the atmosphere but it doesn't entirely stay there so about half of the emission maybe even a bit more than half of the emission that we put in the atmosphere end up in the natural environment it ends up ends up in the ocean and in the forest. So the carbon cycle today absorbed about half of the emissions we put in the atmosphere so we emit as I said 40 gigaton of CO2 per year about half of it 20 gigaton of CO2 are taken back from the atmosphere by the Land and Value Ocean. There's a multitude of different processes that remove carbon dioxide from the atmosphere so for example the CO2 from the atmosphere dissolves in the surface of ocean and then that's turned over and taken into the deep ocean and really for amount of CO2 to be completely removed from the atmosphere it has to be completely dissolved and go down into the deep ocean and then we're talking about geological time scales so hundreds thousands of years. So what happens when we put carbon emissions into the atmosphere new carbon from burning fossil fuel or from deforestation what happens is it take a long time for this carbon to readjust in the land and ocean. Eventually if we're prepared to wait long enough so that's thousands of years a lot of this carbon maybe 70% will end up in the ocean and the reason this takes time is that you have you have different adjustment time so the CO2 goes in the surface ocean it takes about one year to dissolve but how it is transported from the ocean surface to the intermediate and to the deep ocean depends on the ocean circulation and the ocean circulation takes hundreds to a thousand years to mix the entire ocean so that's the time scale that is really relevant here is take a molecule of CO2 we've put it in the atmosphere how long is it going to come take before it ends in the deep ocean. So about 65 to 80% of the carbon dioxide pulse that's put into the atmosphere will be removed within about two to 200 years the rest of it the remaining sort of 35% will take between two and twenty millennia to be completely removed from the atmosphere so roughly you have to think whatever we're doing today whatever CO2 is being emitted roughly a third of it is going to stick around essentially you know forever really when you consider it in our lifetime. We can't change the atmosphere the chemistry with one of the main constituents carbon dioxide by 25% and expect nothing to happen you change your diet by 25% you decide you're gonna start consuming 25% more calories you don't change your exercise or anything else you can't realistically expect nothing to happen and that's what you have to understand that if we change fundamentally our atmosphere chemistry we can't expect climate to stay the same.