The Global Carbon Cycle “It’s not just for scientists anymore…” Rainforest Homework Problem

Surface Temperature Variation (top) Past 140 years, global (bottom) Past 1000 years, N. Hemisphere only

Surface temperature monitoring network 1870 1900 1930 1960

Variations of the Earth’s Surface Temperature - 1000 to 2100 Combined data & model results: 1000 to 1861, N. Hemisphere — proxy data 1861 to 2000, Global — instrumental 2000 to 2100 Global — model projections Variations of the Earth’s Surface Temperature: 1000 to 2100 The projected temperature changes from 2000 to 2100 for the 6 illustrative SRES scenarios are shown in comparison to temperatures observed over the last millennium. The “several models all SRES envelope” shows the temperature rise for the simple model when tuned to a number of complex models with a range of climate sensitivities. All SRES envelopes refer to the full range of 35 SRES scenarios. Source: IPCC TAR 2001

Greenhouse gas increases are driving temperature rise

Indicators of the Human Influence on the Atmosphere during the Industrial Era Concentrations of atmospheric greenhouse gases and their radiative forcing have continued to increase as a result of human activities. Since 1750, carbon dioxide has increased by 31%, methane by 151% and nitrous oxide by 17%. Present concentrations of CO2 and methane are higher now than at any time during the last 420,000 years, the period for which there are reliable ice core data, and probably significantly longer. The current rate of CO2 increase is unprecedented during at least the past 20,000 years. About 75% of the anthropogenic emissions of CO2 to the atmosphere during the past 20 years is from fossil fuel burning, the remainder from deforestation and other land-use changes. The greatest warming effect currently stems from CO2, followed by methane, halocarbons and nitrous oxide. Cooling effects stem from the depletion of stratospheric ozone and generally from relatively short-lived aerosols. Ice cores in Greenland show the large increase in anthropogenic SO2 emissions during the Industrial Era (graph b). Source: IPCC TAR 2001

The CO2 concentration in the atmosphere is strongly correlated with the Earth’s surface temperature

“There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities” “…most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”. IPCC 2001 Global Cycles, Method of analysis: Accounting Cycling and Pathways Controls

The Global Carbon Cycle 1. Accounting (x 1015 g C) Rocks 65,000,000 Oceans 39,000 Soils 1,580 Atmosphere 750 Land Plants 610 Carbon Forms include: Inorganic C (e.g., HCO3-) Organic C Gases (CO2, CH4, CO) The atmosphere is 99.6% CO2

Global Carbon Cycle +7.9 per year Atmospheric CO2 + 3.2 per year 6.3 750 ( @ 360 ppmv) Fossil fuels + 3.2 per year Photosynthesis Land-use Plant respiration Soil respiration 6.3 1.6 Global Carbon Cycle 111 50 60 90 90 92 ~1.4 Net flux ? 1.7 Net flux Vegetation 610 Soils 1580 Ocean 39000 Stock = Billion metric tons Flow = Billion metric tons per year

2. Cycling (a) Pathways (b) Fluxes (in “Peta grams”, Pg = 1015 g = “gigaton” = billion metric tons) 1015 g/year (i) Photosynthesis = - 111 (ii) Respiration = +110 (iii) Net Ocean Uptake = - 1.7 (iv) Fossil Fuels = +6.3 (v) Biomass Burning = +1.6

(c) Mass Balance (of the atmosphere) Net change = Input + Output + Internal Change 3.2 = (110 + 6.3 + 1.6) + (-111 -1.7) + 0 3.2 = (117.9) - (112.7) 3.2 = 5.2 * Need a “sink” of (5.2 – 3.2) = 2.0 Pg C / year to balance the global C budget. Where is the sink?

3. Controls (a) Volcanic Activity (b) Weathering (c) Human influence

Volcanic Activity has a Strong Influence on Atmospheric CO2 over Long Periods of Time

Over Short Periods of Time, Volcanic Activity has a Weak Influence on Atmospheric CO2 Volcanic Emissions = 0.05 Pg C /yr Anthropogenic emissions = 8 Pg C /yr Therefore, human influences are ~160 times more important than volcanoes today.

2. Weathering Reactions Control CO2 in the Atmosphere over Geologic Time

Human Influence on Atmospheric CO2 Increasing trend is modified by seasonal cycle of plant production in the Northern Hemisphere Respiration Photosynthetic uptake

CO2 Emissions from Fossil Fuels and Land Use Change

Projected CO2 Emissions will Increase - Tied to Population Growth -

Projected Changes in Annual Temperatures for the 2050s Although regional patterns are not projected with high confidence, land areas are projected to warm more than the oceans, higher latitude regions (regions closer to the poles) are expected to warm more than equatorial regions, and the Northern hemisphere is projected to warm more than the Southern hemisphere. Projected change compared to the present, assuming ~1%/yr increase in equivalent CO2 Source: The Met Office. Hadley Center for Climate Prediction and Research

Temperature Projections Global average temperature is projected to increase by 2.5° to 10.4°F from 1990 to 2100 Projected rate of warming is unprecedented for last 10,000 years Temperature Projections The global average surface temperature is projected to increase by 2.5 to 10.4°F (1.4 to 5.8°C) over the period 1990 to 2100. These results span the full range of scenarios used in the TAR (35 SRES scenarios). The projected temperature increases are greater than those in the SAR (top end of the range is nearly doubled), which were 1.8 to 6.3°F (1.0 to 3.5°C). The revised higher estimates of projected warming are due primarily to the lower projected sulphur dioxide emissions in the TAR scenarios relative to the SAR scenarios (less of a cooling effect); i.e., a result of the assumption that we will produce fewer pollutants when producing electricity. The projected rate of warming is much larger than the observed changes during the 20th century and is very likely to be unprecedented for at least the last 10,000 years. The magnitude of the warming at the upper end of the range is of the same order as the warming the earth experienced emerging from the depth of the last ice age 20,000 years ago to the warmth of the present interglacial beginning about 10,000 years ago.

How do we solve problems associated with our altered C cycle and increasing CO2 in the atmosphere? The “Geritol Fix” – adding Fe to the Southern Oceans to stimulate algae to take up more CO2 C:Fe = 106:0.01 C:N:P:Fe (!) Element cycles interact! Carbon Sequestration – can something as simple as planting trees be the solution?

Can’t we just plant a bunch of trees? CO2 uptake = 40 CO2 (with 1 N) Net atm change = (20 – 40) = -20 +20 CO2 Plant C:N = 40 20 CO2 OM decomposition Soil C:N = 20 1 N

“There are no magic fixes for the CO2 problem” Take-home message: “There are no magic fixes for the CO2 problem”