Lecture 18 Ecosystems, the Global Carbon Cycle, and Climate

Facts

• CO2 concentration on the rise since Industrial Revolution

• 50% of planetary dry biomass is carbon

• ESMs only created ~25 years ago

• Sources

  • animals

  • plant matter

  • industry

  • deforestation

• Sinks

  • atmosphere

  • ocean: 40,000 mGt of carbon

  • land biota, soil litter, peat: 2,000 mGt

• Fluxes

  • photosynthesis 62 mGt

  • respiration and decomposition 60 mGt

  • physical and chemical processes

What happens to the CO2 we emit?

• Sources

  • 90% from industrial activity, 9.7 GtC/year

  • 10% from land use change, 1.1. GtC/year

• Sinks

  • 48% in atmosphere, 5.2 GtC/year

  • 29% in forests/plants, 3.2 GtC/year

  • 26% in oceans, 2.9 GtC/year

• 4% imbalance

• hard to estimate land stores because there is no mixing, unlike atmosphere and oceans

• terrestrial carbon stores, 1995

  • Vegetation: 610 GtC

  • Soils 1580 GtC

Land Carbon Storage Patterns

• storage of carbon greatest in wooded systems, worst in deserts

  • more carbon below ground in boreal forests

    • frozen, waterlogged soil, short growing period

Global Carbon Budget

• fossil carbon grown as a source massively

• does not match sources to sinks, area of research

Carbon Cycle on Land

• gross photosynthesis

• bole, root, microbial, litter, dark and photo respiration

• CO2 storage

What makes the carbon budget change?

• what makes photosynthesis and respiration change

• resource supply and resource demand

• Photosynthesis

  • 6CO2 + 12H2O -> 6O2 + C6H12O6 + 6H2O

  • temperature, light, etc

  • the carbon that forests remove from the air is much more impactful than the oxygen they release

• Respiration

  • 6H2O + C6H12O6 + 6O2 -> 6CO2 + 12H2O + energy

  • respiration has a 1:1 correlation with temperature, not quite the same in nature

Calculating the carbon balance

• carbon balance = total CO2 in - total CO2 out

• Ways of thinking: models

  • terminology, description with words

  • mapping out a process with pictures

  • representing processes with numbers

  • all MODELS, need to use numbers to estimate quantities

• terrestrial ecosystem process mapped with words: carbon cycle

• or, more detailed with quantities

• carbon is accumulatory

• massive seasonal shifts in carbon sequestration

  • terrestrial biosphere changes with growing period, etc.

  • GPP high in Northern Hemisphere in their summer, low in their winter

• forests highly sensitive to radiation changes

• nitrogen also important

El Nino

• massive effects on carbon balance

• spikes in atmospheric CO2 increase during El Nino events

  • increase in fires in SEA (0.4 GtC 2011-2015)

  • decrease in Gross Primary Productivity (e.g. amount of carbon fixed by vegetation) in South America due to dryness

  • increase in respiration in East Africa due to warmth (0.6 GtC)

Policy Context

• carbon stocks, land use change, and mitigating climate change

• possible to manage increased carbon uptake from forests

  • be specific in where planting trees would do most good

  • REDD: UN policy to reduce emissions from deforestation and degradation

• Houghton et al 2015, showed how investing in tropical forests would pull emissions down faster than just cutting fossil fuel usage