Earth’s carbon balance

The Basic Principle

CO2 is a “greenhouse” gas – it absorbs infra-red radiation as heat

There are other greenhouse gasses, such as CH4 and NO2 but CO2 is the major one

2

How is CO2 measured?

CO2 absorbs infra red radiation

A test gas sample is compared with a reference gas

NOAA monitoring System on Mauna Loa

System for measuring leaf photosynthesis

Infra red gas analyzers

World network

Mauna Loa

US Somoa South Pole

NOAA Stations

Mauna Loa CO2

Trend and annual cycle

International Geophysical Year

Northern hemisphere effectMarch-May maximumSouth pole out of phase

Global growth rate in atmospheric CO2

Influence of economic downturns can be seen

Changes in mean annual global temperature

Sea level rise

Potential effects of sea level rise

Estimates of sea level rise range between 20 and 110 cm by 2100

Why climate change effects on oceans may pose a serious threat

‘In what is being described as "a groundbreaking move for local government", politicians in the Florida Keys have recognised that climate change is likely to threaten their reefs and beaches with severe damage.’

Hurricane George hits Key Westhttp://news.bbc.co.uk/hi/english/sci/tech/newsid_679000/679959.stm

Why climate change effects on sea level poses a serious threat:

Small increases in mean sea level may have large effects during storm conditions, e.g., Florida, Maldives, Bangladesh

Possible changes in ocean currents, e.g., the Gulf Stream and its effects on Northern Europe – dramatic not incremental

Melting of the West Antarctic ice sheet not included in calculating current estimates of sea level increase (potential ~5m rise).

Two Biological Questions

1. Could the earth’s biological systems accumulate sufficient CO2 to balance `emissions?

2. What effects may global change have on the earth’s biological systems?

Summary of the earth’s current carbon balance

All figures are in billions of tonnes of carbon, Gt C1 tonne = 1,000 kilo grams

Anthropogenic release

Net uptake by terrestrial vegetation

Net uptake by the oceans

+6.3

-0.7

-2.3

Gain by the atmosphere +3.3

Net uptake by terrestrial vegetation would have to be increased four-fold to off-set the current rate of increase in

atmospheric C

Could any impact be made as part of a multiple solution approach?

1. Could the earth’s biological systems accumulate sufficient CO2 to balance emissions?

A more detailed look at the global carbon cycle, 1990s

Deforestation contributed between a third an a half of the net gain in the atmosphere. If deforestation were halted then the target for CO2 capture would be less

There is four times as much carbon in the soils and detritus of terrestrial ecosystems as there is in their vegetation

There is approximately five times as much carbon in accessible reserves as there is in the atmosphere

Carbonate in rocks contains the most C by far of any compartment

Net primary production is the difference between the amount of carbon gained by growth of plants minus that lost by respiration and decomposition

Global carbon amounts & net primary production in different biomes

First

Second

tC/ha/yr

Some definitions …

Biome: all organisms, as well as the physical environment, in a particular area. Biomes are usually characterized by their plant life. E.g., Tundra, tropical rainforest.

Biomass: the weight of living material.

SINKS: places where a material, or energy, accumulates

SOURCES: places that produce or supply a material or energy

Tropical forests have the highest biome net primary production and the second highest total biomass. They are strong SINKS for carbon – but if disturbed so that their soil C is respired they can be strong SOURCES

Although temperate forests have the second highest net primary production they have a small global area and so a low total biome C

Note that croplands have a low net primary production. This is because crops usually do not cover the ground for much of the year

Growth of young forests to absorb CO2

“Kyoto Forests”

To balance the net gain of 6 Gt of carbon by the atmosphere through planting young forests, and,

assuming an increase in production of 5 t ha-1 over the vegetation replaced, e.g., replacing a crop,

requires over 109 hectares of young forest, ~14 times the size of Washington State.

Balancing the CO2 input from the US alone would require an area ~3 times Washington State ( ~1.2 times the size of California)

2. What effects may global change have on the earth’s biological systems?

A. Direct effect of elevated CO2

B. Multiple effects of elevated CO2 , elevated temperature, and changed nutrient inputs

C. Possible changes on the distribution range of biomes and crops

A. Direct effect of elevated CO2

Net primary productivity is likely to rise but …

Enhancement declines as the period of CO2 enrichment is extended

Naturally CO2 enriched sites

Acclimation: a change in physiology that enables a plant to maintain a particular pattern or rate of growth, e.g., reduction in stomatal density

CO2 enrichment experiments

FACE: Free Air Carbon Dioxide Enrichment

Brookhaven National Lab

Panama

CO2 is released into the air to achieve an elevated concentration

Experiments are being conducted with a range of crop and vegetation types Catherine Potvin

B. Multiple effects of elevated CO2 , elevated temperature, and changed nutrient inputs

Gain in uptake of carbon may be offset by an enhanced respiration, especially microbial respiration associated with decomposition in the soil and organic litter

Anthropogenic nitrogen from automobile exhausts and agriculture may cause an increase in productivity

C. Possible changes on the distribution range of biomes and crops

Use of global climate change models to predict climate change, along with known present day environmental conditions of different biomes, leads to prediction of major areas of change in vegetation types and that the geographic range of crops will change

Simulated changes in species distributions

Sitka spruce: expansion as coastal region becomes wetter

Douglas fir: some contraction and expansion

No change Contract Expand

Sitka spruce

Douglas fir

Simulated changes in species distributions

No change Contract Expand

Engleman spruce Douglas fir Lodgepole pine Ponderosa pine

Sitka spruce Western red cedar Western hemlock Incense cedar

Information about potential tree species change in the western US can be found at:http://greenwood.cr.usgs.gov/pub/circulars/c1153/c1153_4.htm

1. Substantial changes in tree species distribution are predicted.

3. Similar types and sizes of change have taken place since the end of the last glaciation

2. The changes are individualistic – not the same for all species.

4. Predictions of expansion DO NOT TAKE ACCOUNT of trees dispersal requirements

5. Changes in tree distribution since the last glaciation occurred over ~ 10 thousand years.

A “business as usual” approach to CO2 emissions will lead to a major increase in atmospheric concentrations, doubling by the end of the next century is quite possible

Such a change is bound to have major effects on the earth’s biological and geophysical systems

Conclusions

Sections you need to have read

7.13 35.10 38.4

Courses that deal with this topicThere are many courses and seminars that cover particular aspects of climate change. Two to consider are:

ESC 202 Global Changes and Forest Biology

ATM S 211 Climate and Climate Change

http://www.umac.org/climate/Papers/pg56-64.html