Carbon, Phosphorus and Nitrogen Cycles

Geologist, Alasdair Skelton, explains that there are two parts to the carbon cycle.

The slow part of the carbon cycle operates on timescales of hundreds of thousands of years. On average, 0.1 petagram of carbon dioxide enters the atmosphere from volcanoes and is removed again from the atmosphere by the weathering of rocks, each year.

The fast part of the carbon cycle operates on timescales ranging from seconds to thousands of years. On average 1.7 petagrams of carbon is cycled between vegetation and soils, oceans, lakes and the atmosphere, each year.

Sitting on a rock outcrop alongside Lake Vättern in Sweden, Alasdair Skelton talks about 2019, a year which he calls peak carbon, meaning the year we emitted most carbon to the atmosphere. He explains that by burning fossil fuels and changing how the land is used, we emitted 9 petagrams of carbon to the atmosphere. Most of this carbon (8 petagrams) comes from burning fossil fuels and cement production. These belong to the slow carbon cycle, which means that it will take hundreds of thousands of years for that carbon to get back where it came from.

Surrounded by fields, Alasdair Skelton explains that one fourth of all carbon in the atmosphere was emitted by us since 1950. He links this to global energy consumption has increased by a factor of 5. He links this to population growth but because this has been by a factor of 3 (not 5) he explains that another reason is that we are consuming more energy per person.

With regards population growth, Alasdair Skelton explains that to feed so many people, we have turned to fertilizers which use phosphorus and nitrogen. Phosphorus comes from rocks and is non-renewable. Nitrogen is in plentiful supply but its conversion to fertilizers is coupled with emissions of nitrous oxide, a very potent greenhouse gas.