Anthropogenic Changes and the Atmosphere

Modified: 21 November 2018: expanded section on Nitrous Oxide (N₂O)

POSTED: 14 November 2018

• Climate in The Twentieth and Twenty-first Centuries

• global temperature rose 1.3°C between 1860 and 2017; some 0.6 °C in the century between 1905 and 2005
• greatest increases in 1910-1945 and since 1976
• first may be due to slightly more solar output and lack of global volcanism ⁽⁵⁾
• second is due to injection of greenhouse gases
• warming trend was temporarily offset by 1991 Mt. Pinatubo eruption (by 0.5°C), including the temporary warming by an El Niño
• most glaciers are retreating, including equatorial ice caps and glaciers
• Antarctic ice sheet calves huge ice masses (i.e. of the size of Delaware)
• if the Greenland and Antarctica ice sheets melted completely, global sea level would rise by 65m
• causes for some ice melting are complex, e.g.
  
  • Mt. Kilimanjaro's disappearing ice cap could also be due to local reduction in precipitation as a consequence of local deforestation
  • Antarctic ice sheet is actually growing in some places



• Greenhouse Gases

• H₂O (most important greenhouse gas;
  huge variations due primarily to natural causes, i.e. climate and weather)
• CO₂: amount of CO₂ in atmosphere has increased by 32% from 280ppm in 1800 to 370ppm in 2000, over 400ppm in 2015.

Causes for change: Natural: temporarily also from volcanic activity, but the contribution in historical times has been insignificant Human: burning of biological mass and fossil fuels (80%) Human: removal of rainforest (though the contribution of this is relatively small) (17.3%) as of 2014, Indonesia's rampant deforestation (mainly for oil palm farming) made it #3 in the world's top contributors to anthropogenic CO2 Human: cement production (smaller yet) (2.7%) NB: almost all of the current increase in CO2 is anthropogenic.

• CH₄: has increased 150% from 0.7ppm in 1750 to 1.77ppm in 2000. 1.85ppm in 2018; more effective greenhouse gas than CO₂ but less relevant due to slower current increase. This problem will become more prominent as the population increase requires more farming.

Causes for change: Natural: wetlands (72%) Natural: termites (12.5%) Natural: ocean (6%) Natural: other (9.5%) Natural: recent global warming also releases methane in the tundra that has been "locked" in frozen ground (positive climate feedback) Natural: potential release of large amounts of gas hydrates from submarine icy lenses could happen, if current warming persists (at which point this actually happens is currently unknown) Natural: a natural gas seep off-shore Santa Barbara releases significant amounts though most may be dissolved in water, unless it is transported very quickly to the sea surface Human: coal mining, natural gas, petroleum industry (27%) Human: rice paddies (16%) Human: cattle farming (enteric fermentation, animal wastes)(29%) Human: waste disposal sites (sewage, landfill, biomass burning) (28%) NB: anthropogenic release is currently estimated to be 2.5 times larger than natural release.

• N₂O: nitrous oxide
Causes for change:
• Human: agriculture; main anthropogenic cause
• Human: car and truck engines
• Natural: bacteria growing in soil
• Estimates in 2010 place the anthropogenic/natural ratio at 36/64%.
NB: most of the N₂O is produced by microorganisms is soils and oceans. Anthropogenic sources break down to fertilized agricultural soils and livestock manure (42%), runoff and leaching of fertilizers (25%), biomass burning (10%), fossil fuel combustion and industrial processes (10%), biological degradation of other nitrogen-containing emissions (9%) and human sewage (5%).
• O₃: protects from UV radiation in stratosphere but is a greenhouse gas and a pollutant in the troposphere
Causes for change:
• Natural: changes in solar activity (in stratosphere)
• Human: cars and industry (troposphere)
• CFCs: exclusively of human origin, does not occur naturally; greenhouse gas and destroyer of protecting stratospheric ozone layer; long lived; a single CFC molecule is therefore capable of destroying large amounts of ozone molecules
Sources:
• air conditioning and refrigerators
• foam insulations
• until recently: propellant in aerosol spray cans
• most countries have banned CFCs and other ozone killers but some developing countries still produce CFCs
The increase in greenhouse gases since the Industrial Revolution (mid 1700s) caused an increase of radiative forcing by greenhouse gases by 2.43 W/m². Compare this to a possible increase of 0.3 W/m₂ due to changes in solar output.



• The Industrial Age and CO₂

• CO₂ measured from trapped bubbles in ice cores for times prior to 1958 and direct measurements in atmosphere since then
• industrial revolution at the end of 1700s started a steady increase in CO₂
• increase from 280ppm in 1800 to 370ppm in 2000 to 387ppm in 2008 to 393ppm in 2011; the increase has accelerated within last 50 years

source: NOAA, wikipedia

Keeling curve: Charles David Keeling from SIO established continuous measurements of CO2 on Mauna Loa, Hawaii in 1958; also took measurements at the South Pole that also saw an increase in CO2 seasonal variations (+/- 3ppm) much smaller than overall increase from 318 ppm in 1958 to 400 ppm in 2016 (a 26% increase in 58 years)

• temporarily passed 400 ppm in 2013; 2016 global average above 400 ppm
• current CO₂ level is the highest in last 650,000 years


• the U.S. have been the major contributor (25% of world's CO₂ production!)
• China and India catching up rapidly, with China surpassing U.S.in 2009
• in 2014, the world's largest emitter of greenhouse gases are, in this order: China, U.S., Indonesia ⁽⁶⁾



• Global Increase in Temperature

The link between atmospheric CO₂ increase and temperature increase is difficult to assess since global temperature depends on many factors, not just the atmospheric content of greenhouse gases.
• global temperature rose 1.0°C within last 140 yrs
Possible Reasons:
• millennial warming (<0.02°C)
• solar warming (0.2°C)
• industrial revolution (>0.8°C)
• volcanism (insignificant)
• greatest increases in 1910-1945 and since 1976
• first increase possibly due to increased sun activity (but sunspot maximum was actually in 1950s to 1960s) and lack of volcanism ⁽⁵⁾
• temperatures decreased between 1940 and 1970; the minimum in 60ies-70ies coincides with drop in solar activity
• second increase is most likely due to injection of greenhouse gases
• global average temperature rose by 0.4°C between 1970 and 1990; the current trend is up



• Global Warming and Sea Level Rise

Rising temperatures lead to thermal expansion of the water in the oceans and melting of glaciers and ice sheets. Both results in a rise in sea level.
• In last 100 years, global sea level has risen by 15cm


Estimated contributions to sea level rise:
• thermal expansion: 30%
• melting of glaciers: 20%
• melting of Greenland ice sheet: 20%
• melting of Antarctic ice sheet: unknown but likely large

NB: the melting of sea ice (icebergs) does not contribute to sea level rise! The icebergs floating in seawater already displace the seawater of equivalent weight. So when the icebergs melt, they displace less seawater but the meltwater replaces the "displaced" seawater.


• various model predictions range from 2-5°C warming and a 40 - 100 cm rise in sea level in next 100 years
• this is of the same order as the typical tidal reach and sea surface elevation due to low pressure in a hurricane
• consequences: flooding of coastal areas; landward migration of estuaries; displacement of millions of people
• sea level could rise between 20 and 70 m if all ice sheets melted; estimates vary widely, perhaps because some include thermal expansion of the oceans and some do not



• The Kyoto Protocol

• established in 1997; to be replaced by the Copenhagen protocol in 2009
• in order to stabilize CO₂ at 450 ppm, emission would have to fall below 1990 level
• industrial countries have to reduce to 5.2% below 1990 level by 2012
• need countries responsible of > 50% to ratify
• 96 countries ratified, incl. E.U. and Japan which make up 37.4% of production in industrial countries
• Russia (17.4%) and Poland (3%) initially pledged to ratify the protocol, which would account for 57.8% of production
• jeopardized when Russia bailed out in 2003, but ratified when it joined in October 2004
• in 2012, Canada withdrew
• the Kyoto protocol is opposed by:
  • fossil fuel industry
  • oil-producing countries
  • major fossil fuel users (U.S., China)
• U.S. (25% of total CO₂ and 36.4% of production in industrialized countries, as of 2007) consistently bailed out;
  major argument against ratification: "this would hurt national economy"
  situation improved under Obama who pushes for alternative energies and increased fuel efficiency standards
• European Union and Brazil proposed phasing out fossil fuel burning; Europe has increased the use of alternative energy (e.g. wind), while Brazil has a strong biodiesel program
• new threat: developing countries are catching up (e.g. China, India); some was accounted for in Kyoto Protocol but Warsaw conference in 2013 discusses that it is time for China to participate in reduction of carbon pollution
• annual world climate talks to find successor for Kyoto Protocol have so far failed
• 2006 news clip
• 2013 news clip



• The Kyoto Protocol, next phases

In anticipation of the expiration of the Kyoto Protocol, worldwide meetings have been held every year to agree on a successor to the Kyoto Protocol. Most meetings have failed because the two biggest contributors, the U.S. and China have objected for one reason or another. The 2015 Paris Agreement has come closest, and is now ratified. But the world's biggest worry is that the U.S. will pull out under the new presidency.
• 2009: Copenhagen, Denmark:
• 2010: Cancun, Mexico:
• 2011: South Africa:
• 2012: Qatar, UAE:
• 2013: Warsaw, Poland:
• 2014: UN:
• 2015: Paris, France:
• 2016: Marrakesh, Morocco:



• The Ozone Hole

• Ozone: solar radiation converts O₂ to O₃. Protective layer in 10-50km altitude
• lack in stratospheric ozone lets carcinogenic UV radiation reach the Earth's surface, causing skin cancer, cataracts, impaired immune system, reduced crop yields
• stratospheric ozone attacked by human-made CFC and other halogen componds
• ozone "holes": sharp decrease in thickness of protective ozone layer in stratosphere
• process most effective at low temperatures and in presence of sunlight
• ozone holes therefore near poles; seasonal changes
• ozone destruction most severe in early spring
• decline first noticed in 1980s
• ozone hole caused by human action alone; no natural process known to destroy ozone layer
• chlorofluorocarbons (CFCs) attack and destroy ozone molecules in stratosphere
• sunlight breaks down CFCs; Cl recombines with one of the oxygen atoms of O₃
• CFCs have very long lifetime so can destroy ozone over a long time
• it has been conjectured that the ozone hole will likely increase before the ozone layer recovers, despite recent efforts to reduce CFC input
• Montreal Protocol established in 1987: CFC phased out by 1996 by 140 countries, incl. U.S.
• unlike Kyoto, Montreal was ratified by many because the (sole) human cause of CFC production was more obvious
• effects from CFC reduction not expected to be effective before 2025
• in 2006, the Antarctic ozone hole was the largest ever
• another problem: other halocarbons - like hydrochloro-flourocarbons (HCFC) replaced CFCs. These are less destructive to the ozone layer but are nevertheless greenhouse gases. These will be phased out by 2030. HFCs (hydroflourocarbons) are also greenhouse gases but their lifetime in the atmosphere is significantly shorter than CFCs and HCFCs.
• N₂O also destroys stratospheric ozone.

NB: the ozone hole does not contribute to global warming/global warming and the ozone hole are two phenomena that are not related. Ozone absorbs in the infrared (IR) part of the spectrum, but much more so in the ultraviolet (UV) part. The ozone hole lets more UV light to Earth's surface which does not directly warm the planet.

• Projected Consequences of Global Warming for San Diego

On Nov. 19, 2008 the San Diego Union Tribune released a report written by the San Diego Foundation to the California Climate Action team to describe the consequences of climate change for the San Diego Region by 2050. The Tribune summarized the main projections:


• sea level will be 12-18 inches higher
• the region will require 37% more water while resources (such as the Colorado River) will be less by at least 20%
• the fire season will start earlier; the number of days with ideal conditions for large wildfires will increase by up to 20%
• peak electricity demand will be 70% higher

The summary of the San Diego Foundation actually goes further and says it more bluntly: In 2050, if current trends continue ...
• sea level will be 12-18 inches higher
• San Diego's climate will be hotter and drier
• Wildfires will be more frequent and intense
• We will face severe water shortage
• Public health will be at risk, especially among the elderly and children
• Native plant and animal species will be lost forever
• We will not be able to meet our energy needs

Download summary here. The full report is available at the SDF website.


• Related Web Sites

• Intergovernmental Panel on Climate Change
• Real Climate
• Stephen Schneider at Stanford
• Worldwatch Institute



• References and Recommended Reading

• ⁽¹⁾"Earth's Climate, Past and Future" by William F. Ruddiman, 2000. W.H. Freeman and Company, ISBN: 0-7167-3741-8
  
• ⁽²⁾"State of the World" by The Worldwatch Institute, W.W. Norton and Company.
  Topics change from year to year but here is a short list on recent topics:
  2003 (ISBN: 0-393-32386-2): special 20th Anniversary Edition on spread of and fight against diseases, decline of birds, energy resources, mining and ecosystems, greenhouse effect, Kyoto Protocol, sustainable Earth
  2004 (ISBN: 0-393-32539-3): consumerism and globalization, waste/recycling of resources, catch-up of developing countries, water productivity and increasing shortage.
  2005 (ISBN: 0-393-32666-7): global security, infectious diseases, food security, water, oil economy, postwar societies
  2006 (ISBN: 0-393-32771-X): China and India, global meat industry, freshwater, renewable energy, Mercury, sustainable development, corporations
  2007 (ISBN: 0-393-32923-0): urban future, water and sanitation, urban farming, transportation, energy, natural disaster risks, public health, poverty
  2008 (ISBN: 0-393-33031-1): toward a sustainable global economy, rethinking progress, sustainable lifestyle, low-carbon economy, water, biodiversity, human energy, trade governance
  
• ⁽³⁾check out Worldwatch Institute web site
• "Earthshock" by Andrew Robinson, 1993, Thames and Hudson, ISBN: 0-500-27738-9
• ⁽⁴⁾"Global Warming" by John Houghton, 1999, Cambridge Univ. Press, ISBN: 0-521-62932-2
• ⁽⁵⁾"Natural Disasters" by Patrick Abbott. MacGraw Hill
• ⁽⁶⁾Time, Oct 27, 2014.

1. CO₂
2. CH₄
3. CFCs
4. H₂O

1. thermal expansion of ocean water
2. melting of ice sheets
3. melting of sea ice

1. 12-18 ft
2. 12-18 m
3. 12-18 inches
4. 12-18 cm

1. CO₂
2. O₂
3. CFCs
4. CH₄

1. CO₂
2. O₂
3. CFCs
4. CH₄