Chapter 16 – Global Warming

Elements of this chapter to keep in mind

 analyze and understand anthropogenic global warming and potential policies on global warming from a scientific basis and in the context of past changes in climate – IPPC Ref.

 the relative sizes of the different carbon reservoirs and different carbon fluxes, in particular the size of anthropogenic fluxes compared to natural fluxes  the timescales of the various CO 2 removal processes  stress the chemistry of CO 2 uptake in the oceans  projections for future CO 2 concentrations and predicted climatic implications of global warming , including understanding the level of uncertainty that exists in climate models, and the sources of these uncertainties  anthropogenic gases other than CO 2 contribute to the greenhouse effect  understand how changes in greenhouse gases may affect sea level and ocean circulation, in particular the thermohaline circulation  impact of melting of ice caps – differences between Greenland and Antarctica ice sheets  understand some of the impacts of global warming on ecosystems

Global Warming

• the potential impact of humans on the global climate system • involves links between all the biogeochemical cycles with the earth’s radiation balance • Focus on the carbon cycle, as it has the primary impact: The Greenhouse Effect gtprate gross terr prod beta switch atm ocn2atm respiration rrate weathering oc o2arate wocrate terr decay a2orate atm2ocn goprate surf ocean gross ocn prod liv ing terrestrial bio tdrate weathering cs ocn decay litterf all lrate

revelle switch

wcsrate dead terrestrial bio urate upwell odrate downwell liv ing marine bio drate noprate organic sed osrate net ocn prod deep ocean inorg sed carbonate sediments israte organic c sediments

Global Warming

The Greenhouse Effect

1. Radiation flux (independent variable) as a function of wavelength (dependent variable) Area under curve gives total amount of energy emitted by the two different bodies, similarly for total absorption below 2. Absorption (in %) of different atmospheric constituents as a function of wavelength 3. Note absorption of long wave radiation (infrared) of water vapor and carbon dioxide

The Summary is divided into the following chapters:

•

HUMAN AND NATURAL DRIVERS OF CLIMATE CHANGE

•

DIRECT OBSERVATIONS OF RECENT CLIMATE CHANGE

•

A PALEOCLIMATIC PERSPECTIVE

•

UNDERSTANDING AND ATTRIBUTING CLIMATE CHANGE

•

PROJECTIONS OF FUTURE CHANGES IN CLIMATE

The first four reflect the “detection and attribution” paradigm

HUMAN AND NATURAL DRIVERS OF CLIMATE CHANGE

HUMAN AND NATURAL DRIVERS OF CLIMATE CHANGE

RF = radiative forcing; LOSU = level of scientific understanding

DIRECT OBSERVATIONS OF RECENT CLIMATE CHANGE

DIRECT OBSERVATIONS OF RECENT CLIMATE CHANGE

UNDERSTANDING AND ATTRIBUTING CLIMATE CHANGE

Climate Projections 1. Scenarios

1. Scenarios based on different assumptions about economic, social, technological, and political changes in the future.

2. Assumptions are input into an economic model, which give the fossil fuel usage, and associated carbon emission, as output.

Consumption rates, oil leads the pack

Climate Projections 2. Changes in Atmosphere

1. Emissions from different scenarios are put into carbon cycles models, which keep track of where the carbon goes 2. Other biogeochemical cycle models that might be relevant to climate (e.g. sulfur) are also used.

3. The focus is mostly on atmospheric concentrations, which can affect the radiative balance of the earth

Summary from IPCC

Emissions from fossil fuels and deforestation Assumptions about population and economic growth: a and b – modest growth; c and d more rapid growth a – most optimistic: increase 7 to 10Gton/yr by 2050 then decrease to 5 b – increase by about 0.7%/yr to reach 13Gton/yr by 2100 c – increase such that peak of 17Gton/yr by 2050 and slow decline afterward d – most of energy comes from fossil fuels, reach peak 28Gton/yr (4 x present!!) by 2080; a cumulative of 2000Gtons, almost ½ of all recoverable fossil fuel reserves

Predicted concentrations

a – most optimistic: concentrations of over 500 ppm by 2100 d – concentrations almost twice as high as in case a., 1000 ppm by 2100, 2 doubling since pre-industrial level, first doubling by 2050.

From 1D, radiative-convective CM: doubling CO 2 increases global temperature by 2.5ºC (with H 2 O feedback), doubling it twice can lead to an increase of 5ºC (9ºF) over the next century.

Note that so far warming is about 1ºC (0.7ºC), so these predictions indicate that our climate might warm faster than in the past.

Radiative forcing from other gases

Carbon dioxide, methane and nitrous oxide - all linked to population, anthropogenic activities, agriculture, etc. all contribute to the

radiative forcing

(= change in outgoing IR radiation flux due to change in concentration of these gases) Doubling CO 2 - 4.4 W/m leads to 2.5ºC increase in 2 , which temperature according to SCMs, or 1.5-4.5ºC in GCMs From the figure: CO 2 CH 4 - 0.5 W/m 2 , CO 2 - 1.5 W/m 2 - 0.15 W/m over the past 1000 years , 2

Our C-cycle lab, scenario 1

Our C-cycle lab, scenario 2

Our C-cycle lab, scenario 3

Our C-cycle lab, scenario 4

Climate Projections 3. Changes to the Climate System

1. changes in atmospheric composition are put into a climate model, which calculates the radiative balance of the earth, and the resulting changes in the distribution of energy and temperature 2. particular attention is paid to surface air temperatures and to sea level rise – shown in the figure is predicted trends in global Ts for the four scenarios described before IPCC 2001

IPCC 2007

Climate Projections 3. Changes to the Climate System

1. changes in atmospheric composition are put into a climate model, which calculates the radiative balance of the earth, and the resulting changes in the distribution of energy and temperature 2. particular attention is paid to surface air temperatures and to sea level rise – shown in the figure: Predicted sea-level change for the four scenarios described earlier; range: 30 cm for scenario a. to 50 cm for case d. IPCC 2001 Note: the concern is with the rate of increase, as this shows that it would be 2 to 3 times faster than the rate of increase in the past century

Climate Projections 4. Uncertainties

1. Uncertainties in every step are addressed: 2. Economic, technological, carbon cycle, and social uncertainties are addressed by including a large number of scenarios 3. Climate model uncertainties are addressed by including ranges of results from different models IPCC 2001

IPCC 2007 2007

PROJECTIONS OF FUTURE CHANGES IN CLIMATE

take-home messages:

Sea Level Rise

1. caused by an increase in the

volume

of water stored in the oceans. What causes this increase in volume? Increase amount, decrease density 2. increase in the

amount

: Melting of ice that is on land 3. decrease in the density

: thermal expansion

4. estimates of local impacts must include local vertical movements due to

glacial rebound

,

sedimentation changes

, and other local effects global sea level follows global temperature trend about 12 cm since 1880

Sea Level Rise

Sources of land-ice that might have contributed to past, and could contribute to future, global sea level rise: 1.

Glaciers: believed to have contributed about half of past century’s global sea level rise (the other half due to thermal expansion) 2.

3.

Greenland ice sheet: contains enough water to raise sea level by 7 meters; previous contribution to sea level rise is unknown, but most likely had a

positive

contribution (lost mass during the past few decades). Antarctic ice sheet: contains enough water to raise sea level by > 60 meters (East Antarctica) but it may melt less than Greenland’s. Also snowfall may increase over Antarctica thickening the sheet over next century, therefore global sea level MIGHT decrease instead. Ice flow on West Antarctica is dynamic, and its potential response to climate change is unknown. 4.

West Antarctica: less water but behaves differently – here ice flows and forms ‘floating chunks’ (ice shelves) of ice grounded off the continents, if temperature increases, they may become free-floating ice, generates friction, hence more heat, hence more melting! This can add SIGNIFICANTLY to present prediction of sea level rise due to Greenland’s ice sheet melt (which is most likely).

West Antarctica

Ice Shelves: are grounded at several points offshore; affected by water temperatures; if they are removed, ice will flow faster

Ice Flow

Sea level rise due to 1. Thermal expansion - half of rise

* 0.7 °C during 20th century responsible for about 7 cm rise * changes in deep ocean: very slow, mostly due to Milankovitch cycles which can be responsible for 5 msea-level fluctuations over longer period (recorded)

2. Melting of mountain glaciers - this has been in the news as being much faster and more widespread as previously thought

Changes in thermohaline circulation – possible impact

Possible changes to N. Atlantic downwelling, which could affect regional temperatures. If the N. Atlantic freshens sufficiently, downwelling might decrease, or cease, leading to cooler surface ocean and cooler regional climate.

Possible effects on ecosystems

1. Different plant species more adapted to higher CO2 and higher temperature levels. e.g. C3 plants are expected to increase productivity at elevated CO2 levels more than C4 plants; this could affect agriculture.

2. Forest composition expected to vary, depending on temperature and other environmental controls 3. Plant and animal migrations expected to affect ecosystems; different than earlier events because of speed of change, and disruption of migration paths by human settlement

Economics of Climate Change

1.

2.

3.

Intergenerational equity

: benefiting from things for which future generations will have to pay; discounting costs and benefits

Other equity issues

: “Developing” vs “developed” countries: who is more responsible, those who emitted in the past, or those in the future?

Externalized costs

: Some of the costs associated with “a product” are paid for by society in general, not the polluter. So, cost of cleaning up are not included in the price.

Policies to mitigate global warming

1.

Conservation

– use less energy (not likely to happen); plant trees;

2.

Alternative energy –

using energy from non fossil-fuel (non greenhouse emitting) sources.

3.

Nuclear, wind, tidal, geothermal, biomass-based fuels, solar Methods to decrease CO2

emissions

.

CO2 tax

– extra tax on high-CO2 emission fuels; tax determined by mpg regulations;

carbon sequestration