Biology 381, Pollution Biology

Department of Biological Sciences,
Faculty of Science,
University of Alberta,
Edmonton, Alberta.

10. Global climate change and the enhanced greenhouse effect.

10.1 Required reading and other announcements.

World Wide Web resources provide excellent reference materials. Links to the WWW are optional reading.

10.2 An overview of the problem.

In 1896, the Swedish chemist Svante Arrhenius calculated that a doubling of atmospheric carbon dioxide (CO₂) would make Earth several degrees warmer.

A century later, we are beginning to understand the processes which create and influence our climate and the effect we might have on it.

The Earth's atmosphere is largely transparent to incoming short wave radiation from the sun.

Short wave radiation is absorbed at/near the Earth's surface, converted into heat (infrared radiation), and radiated back into the atmosphere.

Greenhouse gases absorb infrared energy, causing the temperature of the atmosphere to rise.

http://www.puc.ohio.gov/gcc/sciover.html.

As the concentrations of greenhouse gases in the atmosphere increase, so too does the amount of infrared radiation absorbed. Hence, the earth and its atmosphere get warmer.

The enhanced greenhouse effect has the potential to significantly affect global climate.

The nature and extent of these changes is still a matter of considerable debate.

10.3 Anthropogenic greenhouse gases (GHGs).

Two factors determine whether a greenhouse gas (GHG) has a quantitatively important effect on global climate.

• The concentration of the GHG in the atmosphere.

  The absolute concentration of a GHG at any time will reflect a balance between "sources" and sinks.

• The extent to which the GHG absorbs infrared energy.

  The relative warming potential or Global Warming Potential (GWP) of a GHG is a function of the absorptive properties of the gas, and its residency in the atmosphere.

Important greenhouse gases
Greenhouse gas	Abbreviation	Concentration	Global Warming Potential
Water	H20	variable	high
Carbon dioxide	CO2	high (102 ppm)	low (1.0)
Methane	CH4	moderate (ppm)	moderate (21)
Chlorofluorocarbons	CFCs	very low (ppt)	high (3,400-13,000)
Nitrous oxide	N2O	low (ppb)	moderate (310)
Hydrochlorofluorocarbons	HCFCs	very low (ppt)	mod., high (90-2000)
Hydrofluorocarbons	HFCs	very low (ppt)	mod., high (140-12,100)
Ozone	O3	variable	low

To evaluate the total "radiative forcing" of a GHG, the Global Warming Potential (GWP) must be multiplied by the actual mass of emissions.

http://www.puc.ohio.gov/gcc/sciover.html.

What subset of greenhouse gases should be the focus of global efforts to control the enhanced greenhouse effect?

10.4 Concentrations of greenhouse gases are increasing.

Anthropogenic emissions of greenhouse gases have risen sharply since the industrial revolution.

Estimated concentrations of greenhouse
gases (1750 and 1992).

Greenhouse Gas	1750 Concentration	1992 Concentration
Carbon Dioxide	280 ppmv	355 ppmv
Methane	0.8 ppmv	1.72 ppmv
Nitrous Oxide	275 ppbv	310 ppbv
CFC-11	0	280 pptv
CFC-12	0	484 pptv
HCFCs/HFCs	0	n/a
Tropospheric Ozone	n/a	variable
Stratospheric Ozone	n/a	300 DU

Note: ppmv=parts per million by volume, ppbv=parts per billion by volume,
pptv=parts per trillion by volume.
http://www.puc.ohio.gov/gcc/sciover.html.

Source: International Consortium of Local Environmental Initiatives, Toronto, Canada, or see
http://www.puc.ohio.gov/gcc/sciover.html.

Concentrations of CO₂ in the atmosphere have increased by approximately 25%, from 270-280 ppm 250 years ago, to approximately 350 ppm today.

Changes in atmospheric CO₂ concentrations measured at Mauna Loa, Hawaii : 1958-1991

http://www.puc.ohio.gov/gcc/sciover.html.

By all indications, concentrations of CO₂ will continue to increase for the foreseeable future.

http://www.globalchange.org/dataall/95jul5l.htm.

The International Energy Agency's "Capacity Constraints" estimate of global energy-related CO₂ emissions for the years 2000 and 2010.

10.5 Predicting the impact : General Circulation Models.

Scientific progress has not produced simple answers. If anything, recent research confirms the complexity of the climate system.

Considerable uncertainty about the scale, the timing, and the regional distribution of global warming remains.

General Circulation Models have served to highlight our lack of understanding about global climate.

Climate Modeling and the case of the missing carbon.

• A clear picture of the global carbon budget continues to elude climate researchers.

• As yet, the carbon output of major sources (approximately 7.6 billion tones) cannot be accurately determined.

• Accounting for the amount of carbon in sinks is even more difficult.

• The atmosphere, the ocean, and the land with its plants and animals comprise the world's three major carbon sinks.

• The only sink whose carbon content is known with any certainty is the atmosphere.

• More than 2 billion tons of carbon per year are unaccounted for.

• Some scientists have argued that this is the amount of carbon in the terrestrial sink, that stored by the world's plants as increased growth.

• Will the terrestrial sink continue to function as in the past, or will natural biological limits or climate changes brought on by global warming diminish its storage capacity?

• The continued ability of temperate forests to absorb new carbon is anything but assured.

Climatologists have quickly moved to incorporate the latest findings into their General Circulation Models.

The projected rise in global mean temperature from 1990 to 2100 is 2.5° C, compared with 3.3°C calculated by older models.

Such changes may seem insignificant, but climate shifts of this magnitude have not been experienced since the last deglaciation some 10,000 years ago.

But, General Circulation Models remain flawed in several key areas.

• The greatest source of uncertainty concerns clouds, which play an important role in regulating Earth's radiation.

• Ocean dynamics are a second major area of concern for modelers.

• A third area of uncertainty involves atmospheric chemistry.

• A final source of uncertainty for modelers is the biosphere's reaction to greenhouse conditions.

• While these uncertainties raise doubts about the extent of global climate change, climatologists still emphasize that a continued increase in greenhouse gases will heat up the Earth over time.

10.6 Current evidence indicates global climate may be changing.

Reexamination of historical records suggests that global mean temperatures have risen 0.3 to 0.6°C over the past 100-130 years.

http://www.ncdc.noaa.gov/gcps/papers/climchg/climate-change-update.html.

Eight of the hottest years in the temperature record occurred between 1980 and 1992.

Now that the effects of Mt. Pinatubo have diminished, temperature records are being set again.

The rapid melting of glaciers in temperate regions over the last 30 years also suggest a warming trend.

Borehole data also point to a rise in surface temperatures of 1 - 1.5^o C over the past 100-150 years.

However, it is still hotly debated whether all or part of this century-old trend can be explained by human contributions to the greenhouse effect.

The extent of current warming has not exceeded the limits of natural climate variability.

10.7 Dramatic shifts in global climate?

The Earth's oceans are one of the most important factors shaping global climate.

• They absorb heat trapped by greenhouse gases.

• They are climate stabilizers.

• They can also occasionally instigate dramatic climate shifts.

Ocean Circulation and Climate Shifts.

• Historical alterations in ocean circulation patterns may have triggered temperature changes of more than 5° C within 50 years or less.

  http://windows.engin.umich.edu:80/earth/images/rectangle_mike_image.html.

  

  http://dcz.gso.uri.edu/amy/avhrr.html.

• Some scientists have theorized that deep oceanic currents can be interrupted.

• Periodic stalling and renewal of current flow, and hence heat transport, could explain the discontinuous warming that characterized the world's emergence from the last ice age.

• The fear today is that greenhouse warming could prevent the formation of North Atlantic deep water.

• Rapid climate fluctuations in the wake of stalled oceanic currents could severely affect the functioning of the biosphere. Few ecosystems would have time to adapt to the temperature shifts.

A positive feedback loop?

• Formation of deep water is an important mixing mechanism in the ocean. The rate of mixing is the limiting factor in determining how much CO₂ the ocean can absorb from the atmosphere.

• A stalled current could substantially reduce the ocean's role as a sink for CO₂.

• This could initiate what is effectively a positive feedback loop.

10.8 Less warming that expected?

Ozone depletion and airborne particulates have had a cooling influence over some regions of the globe. Thus, greenhouse warming has been less pronounced than expected.

Recent evidence suggests that the heat-trapping properties of CFCs may be more than offset by stratospheric cooling which results from stratospheric ozone depletion.

These competing effects of CFCs are not necessarily reassuring.

Atmospheric aerosols and particulates also have a significant cooling effect.

It is not clear to what extent aerosol shading and greenhouse warming will cancel each other out.

Like cooling from ozone-depletion, aerosol cooling is uneven and may initiate large-scale changes in climate.

Modelled geographical distribution of contemporary annual mean direct radiative forcing (Wm^-2) from anthropogenic sulfate aerosols in the troposphere.
http://www.ncdc.noaa.gov/gcps/papers/climchg/climate-change-update.html.

10.9 What impacts might be possible?

One of the projected impacts of the enhanced greenhouse effect will be a increase in temperature.

• Increases in mean global temperatures will not be evenly spread over the globe.

  http://www.ncdc.noaa.gov/gcps/papers/climchg/climate-change-update.html.

• Warmer temperatures could result in more extreme weather such as severe droughts and/or floods

Large scale melting of ice is predicted to raise sea levels.

• Global warming could cause sea levels to rise in two ways, through thermal expansion of ocean water, and through the shrinking of ice caps and mountain glaciers.

• Higher sea levels would threaten low lying coastal areas.

• Recent changes in sea levels generalized over the globe.

  http://www.ncdc.noaa.gov/gcps/papers/climchg/climate-change-update.html.

Global warming may increase rates of desertification.

Effects of climate change on agricultural productivity will be difficult to predict.

• Higher levels of CO₂ should stimulate photosynthesis in C3 plants.

• However, climate and agricultural zones would tend to shift towards the poles.

• Some species would benefit from higher temperatures, others might not.

• Mid-latitude yields may be reduced by 10-30% due to increased summer dryness. This could also exacerbate pest/pathogen interactions.

Ecosystem level effects.

• Shifts in climate could shift the competitive balance among species, particularly as it relates to C3 and C4 plants.

• The composition and geographical distribution of many ecosystems will shift as many species respond to climate.

• As much as 30% of the world's forests may undergo broad changes in vegetation types.

• Forest dieback and melting of permafrost could alter patterns of terrestrial uptake and release of carbon.

• More extreme weather events could increase the incidence of fire, and pest outbreaks, perhaps resulting in changes in and ecosystem structure and function.

Effects on human health.

10.10 Working towards a solution.

Uncertainties about the impact of the enhanced greenhouse effect will continue to plague forecasts for several more decades.

However, the international scientific community is now moving toward a consensus regarding the potential for global climate change.

Action to control the enhanced greenhouse effect may require a major shift in human lifestyle with a significant economic cost.

If carbon dioxide emissions were maintained at 1994 levels, this would still lead to an increase in atmospheric concentrations for at least two centuries, approaching a doubling of pre-industrial levels (from 280 to 500 parts per million volume) by the end of the 21st century.

Are we ready for such changes?

10.11 An emerging international effort.

The key international initiative aimed at controlling global climate change is the United Nations Framework Convention on Climate Change (FCCC).

• The FCCC (1992-94) is the first international legal instrument dealing directly with climate change.

• The Convention's objective is the "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system."

• This objective is to be achieved within a time frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production in not threatened, and to enable economic development to proceed in a sustainable manner.

• One of the important general commitments is to adopt national programmes for mitigating climate change.

• Developed countries have agreed to take measures designed to limit emissions of carbon dioxide and other greenhouse gases, with the aim of reducing emissions to 1990 levels by the year 2000.

• The convention that has been signed by most countries on the planet, with signatories accounting for 88% of global CO₂ emissions.

  

  http://http://www.globalchange.org/dataall/95jul1l.htm.

  Percentage of global CO₂ emitted by signatories to the Framework Convention on Climate Change.

  

  http://www.globalchange.org/dataall/95jul2l.htm.

One of the more positive offshoots of the Framework Convention on Climate Change is the formation of the Intergovernmental Panel on Climate Change.

The IPCC was one of the first to sound the warning that many of the goals set out in the FCCC may not be met by the target date of 2000.

10.12 Additional world wide web information.

IPCC Second Assessment Synthesis ... (1995). - One of the most up to date and authoritative references available.

Global Change, The Electronic Edition. - An absolute wealth of information on global climate change. Everything you wanted to know if you have the time to look.

The Intergovernmental Panel on Climate Change's fact sheet series A major source of fact sheets on Global Change.

The Public Utilities Commission of Ohio's overview of global climate change. - A strong review of the basics.

Global Change's Guide to IPCC-Related Publications - A list of sources for information on Global Change.

Last updated, March 16, 1997