Unit 9 Beta

Global Change: the one-page sheet

9.1 Stratospheric Ozone Depletion

The stratospheric ozone layer absorbs most of the Sun’s UV. CFCs drift up to the stratosphere, where UV frees chlorine, and each chlorine atom destroys many thousands of ozone molecules because it is released again after each cycle. The ozone hole forms over Antarctica each spring. Thinner ozone lets more UV-B through, raising skin cancer and cataracts. Carbon dioxide is not an ozone-depleting gas.

Chlorofluorocarbons (CFCs) contain chlorine, fluorine and carbon. They were used in refrigerators, air conditioners, foams and spray cans because they are stable and nontoxic near the ground.
In the stratosphere, UV frees chlorine; $\text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2$ , then $\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2$ . The chlorine is reused.
Ozone depletion is worst over Antarctica each spring (the ozone hole), where extreme cold forms clouds that speed the reactions.
More UV-B at the surface means more skin cancer and cataracts and damage to phytoplankton and crops.

they last long enough to drift up into the stratosphere chlorine atoms are set free one atom can destroy many thousands of ozone molecules more UV-B reaches the surface, raising skin cancer and cataracts and harming phytoplankton

chlorofluorocarbon: Chlorofluorocarbons (CFCs): stable, nontoxic gases of chlorine, fluorine and carbon once used as refrigerants, propellants in spray cans and in foams. In the stratosphere, UV breaks them and frees chlorine that destroys ozone.
ozone depletion: The thinning of the stratospheric ozone layer by chlorine and bromine from CFCs and halons. The ozone hole is the severe seasonal thinning over Antarctica each spring.

9.2 Reducing Ozone Depletion

The Montreal Protocol of 1987 phased out CFCs, halons and other ozone-depleting substances worldwide. HCFCs were a stopgap that still contains chlorine; HFCs spare ozone but trap heat, so the Kigali Amendment phases them down. Hydrocarbon and other refrigerants and capture of old refrigerant help too. Ozone is recovering slowly because CFCs last for decades.

The Montreal Protocol (1987) is the treaty that phased out CFCs, halons and other ozone-depleting substances. Every UN member has ratified it.
HCFCs were a temporary replacement: less ozone-depleting, but they still contain chlorine, so they are being phased out too.
HFCs contain no chlorine and do not harm ozone, but many trap heat thousands of times more strongly than CO₂. The Kigali Amendment (2016) phases them down.
Other fixes: hydrocarbons such as isobutane, ammonia and CO₂ as refrigerants, and capturing refrigerant from old equipment.

nations signed the Montreal Protocol in 1987 production of ozone-depleting substances fell by more than 99% far less chlorine reaches the stratosphere ozone is recovering and should return to 1980 levels around 2066 over Antarctica

Montreal Protocol: The 1987 international treaty that phased out the production of CFCs, halons and other ozone-depleting substances; it has been ratified by every UN member state.
hydrochlorofluorocarbon: Replacements for CFCs. Hydrochlorofluorocarbons (HCFCs) still contain some chlorine, so they deplete a little ozone and are being phased out. Hydrofluorocarbons (HFCs) contain no chlorine and spare ozone, but many trap heat strongly and are being phased down under the 2016 Kigali Amendment.

9.3 The Greenhouse Effect

Sunlight warms the surface, which gives off infrared; greenhouse gases (water vapor, CO₂, methane, nitrous oxide, CFCs) absorb it and send part back down, keeping Earth about 33 °C warmer. More gas traps more heat. Global warming potential compares gases with CO₂: multiply a mass by its GWP for CO₂ equivalent. The greenhouse effect is not ozone depletion.

The greenhouse effect: greenhouse gases absorb infrared radiation given off by the surface and re-emit part of it downward, warming the lower atmosphere.
Greenhouse gases: water vapor (most abundant), carbon dioxide, methane, nitrous oxide (N₂O) and CFCs and HFCs. SO₂ and particulates are not greenhouse gases.
Global warming potential (GWP) compares the heat trapped by a gas with the same mass of CO₂ over 100 years: CO₂ 1; methane roughly 25 to 30 (the IPCC value depends on the report); N₂O roughly 265 to 300; CFCs thousands. A calculation question gives you the GWP to use.
The natural greenhouse effect keeps Earth about 33 °C warmer than it would be. Ozone depletion is a separate problem: UV and the stratosphere.

it warms Earth’s surface greenhouse gases in the troposphere absorb much of it the lower atmosphere and surface stay warmer than they would be traps more heat, strengthening the effect and raising temperatures

infrared radiation: Infrared radiation (IR): invisible radiation with longer wavelengths than visible light, given off by warm objects such as Earth’s surface. Greenhouse gases absorb it.
greenhouse gas: A gas that absorbs and re-emits infrared radiation, warming the lower atmosphere: water vapor, carbon dioxide, methane, nitrous oxide, CFCs and HFCs (GHGs).
greenhouse effect: The warming of Earth’s surface and lower atmosphere because greenhouse gases absorb infrared from the surface and re-emit part of it downward. The natural effect keeps Earth about 33 °C warmer; added gases strengthen it.
global warming potential: Global warming potential (GWP): how much heat a mass of a gas traps over a set time, usually 100 years, compared with the same mass of carbon dioxide (GWP 1). Mass × GWP gives the CO₂ equivalent.
nitrous oxide: Nitrous oxide (N₂O): a greenhouse gas that traps roughly 265 to 300 times as much heat as the same mass of CO₂ over 100 years (the IPCC value depends on the report), released mostly by fertilized soils, manure and burning fuel. It lasts over a century in the air.

9.4 Increases in the Greenhouse Gases

Burning fossil fuels and clearing forests add CO₂; livestock, rice paddies, landfills and gas leaks add methane; fertilizer adds nitrous oxide. The Keeling curve shows CO₂ at Mauna Loa rising from about 317 ppm in 1960 to over 420 ppm, faster each decade. Ice cores show it stayed between about 180 and 300 ppm for 800,000 years.

CO₂ sources: burning fossil fuels (largest), deforestation, cement. Methane: livestock, rice paddies, landfills, natural gas leaks. Nitrous oxide: fertilizer and manure.
The Keeling curve: CO₂ measured at Mauna Loa since 1958. It rises every year, faster each decade, with a small yearly wiggle from Northern Hemisphere plants.
Ice cores hold bubbles of ancient air: CO₂ stayed between about 180 and 300 ppm for 800,000 years and was about 280 ppm before 1800.
Today: over 420 ppm, about 50% above the level before 1800.

carbon stored for ages enters the air as CO₂ add methane; fertilizer adds nitrous oxide the concentration of greenhouse gases keeps rising they show CO₂ above 420 ppm, far above its 800,000-year range

Keeling curve: The record of atmospheric carbon dioxide measured at Mauna Loa Observatory, Hawaii, since 1958 by Charles David Keeling and later NOAA. It rises every year with a small seasonal cycle.
ice core: A long cylinder of ice drilled from a glacier or from the thick ice of Antarctica or Greenland. Bubbles of air trapped in the ice record past greenhouse gas levels going back hundreds of thousands of years.

9.5 Global Climate Change

More greenhouse gases warm Earth. Warming melts land ice, which raises sea level, and melts sea ice, which does not raise sea level but lowers albedo. Positive feedback loops such as melting ice and thawing permafrost amplify warming. Effects include heat waves, droughts, heavy rain, coastal flooding and species shifting toward the poles.

Climate change: long-term change in Earth’s climate, now mainly warming caused by added greenhouse gases.
Sea level rise comes from melting land ice (glaciers, ice sheets) and from warming water taking up more space. Melting sea ice does not raise sea level, because it already floats.
A positive feedback loop amplifies a change: melting ice lowers albedo; thawing permafrost releases methane and CO₂.
Effects: heat waves, shifts in rainfall, stronger storms, coastal flooding, coral bleaching, species moving toward the poles.

global average temperature rises (about 1.1 °C since the late 1800s) water flows into the ocean and sea level rises albedo falls and stored carbon is released: positive feedback loops amplify warming heat waves, droughts, heavy rain and species range shifts become more common

climate change: A long-term change in Earth’s climate. Global climate change today means warming caused mainly by greenhouse gases from human activity, and its effects on sea level, weather and ecosystems (global warming is the temperature part).
sea level rise: The rise in average ocean height, caused by melting land ice and by seawater expanding as it warms. Melting floating sea ice adds almost nothing.
positive feedback loop: A loop in which the result of a change strengthens that change, such as melting ice lowering albedo, which causes more warming and more melting.
land ice: Ice on land: glaciers and the ice sheets of Greenland and Antarctica. Its melt raises sea level. Sea ice, frozen seawater floating on the ocean, does not raise sea level when it melts.

9.6 Ocean Warming

The ocean absorbs about 90% of the extra heat. Warmer water expands (thermal expansion), which with melting land ice raises sea level. Warm water holds less oxygen and mixes less, so oxygen and surface nutrients fall. Heat stress bleaches corals and pushes species toward the poles. The thermohaline circulation, driven by temperature and salinity, could slow as fresh meltwater enters the North Atlantic.

The ocean has absorbed about 90% of the extra heat trapped since 1970.
Thermal expansion: warmer water takes up more space. With melting land ice, it causes most sea level rise. It is caused by heat, not by dissolved CO₂.
Warming lowers dissolved oxygen, bleaches corals, shifts species ranges and makes the surface layer mix less with nutrient-rich deep water.
The thermohaline circulation (ocean conveyor belt) is driven by temperature and salinity; fresh meltwater could weaken it.

the ocean absorbs about 90% of it, because water stores heat well sea level rises, alongside water from melting land ice oxygen falls and fewer nutrients reach the surface corals bleach, fish move toward the poles, and currents can change

thermal expansion: The increase in volume of water as it warms. Thermal expansion of seawater is one of the two main causes of sea level rise, with melting land ice.
thermohaline circulation: Thermohaline circulation (the ocean conveyor belt): the slow global movement of deep ocean water, driven by differences in temperature and salinity, which set the water’s density.

9.7 Ocean Acidification

The ocean absorbs part of the CO₂ people add to the air. Dissolved CO₂ forms carbonic acid, which releases hydrogen ions and lowers pH; those ions also bind carbonate, so corals, oysters and some plankton struggle to build calcium carbonate. pH has fallen from about 8.2 to 8.1; because the scale is logarithmic, that is about 26% more hydrogen ions. Cutting CO₂ emissions is the fix.

Ocean acidification: seawater pH falls as it absorbs CO₂. Average surface pH has dropped from about 8.2 to about 8.1 since the 1700s and could reach about 7.8 by 2100 if emissions stay high.
Chemistry: $\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3$ (carbonic acid) $\rightarrow \text{H}^+ + \text{HCO}_3^-$ ; then $\text{H}^+ + \text{CO}_3^{2-} \rightarrow \text{HCO}_3^-$ removes carbonate.
The pH scale is logarithmic: hydrogen ions multiply by $10^{\text{drop}}$ . A drop of 0.1 is about 26% more H⁺; a drop of 0.3 is about twice as much.
The ocean is still basic (pH above 7); "acidification" names the direction of change.

the ocean absorbs about a quarter of it it releases hydrogen ions, so pH falls less carbonate is left for building calcium carbonate reefs weaken and food webs that depend on them suffer

ocean acidification: The decrease in the pH of seawater as it absorbs carbon dioxide from the air. Surface ocean pH has fallen from about 8.2 to about 8.1 since the 1700s.
carbonic acid: Carbonic acid (H₂CO₃) forms when CO₂ dissolves in water and releases hydrogen ions. Those ions bind carbonate ions (CO₃²⁻), leaving less for organisms to build calcium carbonate (CaCO₃) shells and skeletons.

9.8 Invasive Species

Invasive species are nonnative species that spread quickly and cause harm. They are often generalists with r-selected traits that face few predators in their new home. They outcompete natives and are very hard to remove once established. Zebra mussels, kudzu and cane toads are classic cases. Prevention, such as ballast water rules and boat cleaning, and early detection are the best tools.

Invasive species are nonnative (exotic) species that spread quickly and cause harm. Not every nonnative species is invasive.
They are often generalists with r-selected traits. Lacking natural predators is a feature of the new ecosystem, not a trait.
Examples: zebra mussels (ballast water, Great Lakes), kudzu (planted for erosion control), cane toads (brought to Australia for pest control), Asian carp, emerald ash borer.
Control: prevention (ballast rules, boat cleaning, inspections), early detection, removal, and carefully tested biological control.

it arrives where it has few predators, parasites or diseases its population grows explosively native populations decline and biodiversity falls prevention and early detection are the best control

invasive species: A nonnative (exotic) species, moved by people outside its native range, that spreads quickly and harms ecosystems, the economy or health. Many are generalists with r-selected traits.

9.9 Endangered Species

Endangered species face extinction now; threatened species likely will soon. Specialists, K-selected species, small populations and species that need large territories are most at risk. The US Endangered Species Act protects listed species and their critical habitat, and CITES controls international trade. Recovery works when the cause of decline is removed, as with the bald eagle after DDT was banned.

Endangered species: in danger of extinction in all or much of its range. Threatened species: likely to become endangered soon.
Most at risk: specialists, K-selected species, small or isolated populations, species needing large territories, those hunted or traded.
The Endangered Species Act (US, 1973) lists species, bans harming them and protects critical habitat. CITES is the international treaty controlling trade.
Recoveries: bald eagle (DDT ban plus protection), California condor and black-footed ferret (captive breeding and release).

cannot easily shift to new food or habitat and replace losses slowly they become threatened, then endangered they are more vulnerable to disease and change can stop the decline and let numbers recover

endangered species: A species in danger of extinction throughout all or a significant part of its range. A threatened species is one likely to become endangered in the foreseeable future.
Endangered Species Act: The Endangered Species Act (US, 1973) lists threatened and endangered species, bans harming them and protects their critical habitat. CITES, an international treaty, controls trade in protected species and their parts.

9.10 Human Impacts on Biodiversity

Human impacts on biodiversity are summed up as HIPPCO: habitat loss (the leading cause), invasive species, pollution, human population growth, climate change and overexploitation. Fragmentation leaves small, isolated populations that are easily lost. Today’s extinction rate may mark a sixth mass extinction. Protected areas, wildlife corridors, catch limits and restoration help reverse the losses.

HIPPCO: Habitat loss, Invasive species, Pollution, human Population growth, Climate change, Overexploitation. Habitat loss is the leading threat.
Fragmentation creates small, isolated patches that hold fewer species and lose them faster.
Wildlife corridors (strips of habitat, overpasses, underpasses) reconnect fragments so animals can move, mate and recolonize.
Species are being lost tens to hundreds of times faster than the background rate, which may mark a sixth mass extinction.

habitat is lost and broken into small, isolated fragments they lose genetic diversity and are easily wiped out species are lost far faster than the natural background rate slow the losses and let populations recover

habitat loss: The destruction or conversion of the places species live, by farming, logging, mining, roads and cities (habitat destruction). It is the leading cause of biodiversity loss.
HIPPCO: An acronym for the main human threats to biodiversity: Habitat loss, Invasive species, Pollution, human Population growth, Climate change and Overexploitation.
wildlife corridor: A strip or link of habitat, such as a forested strip, an overpass or an underpass, that connects fragments so animals can move between them (also called a habitat corridor).
mass extinction: The loss of a large share of Earth’s species in a geologically short time. Five have occurred; today’s rapid losses may mark a sixth mass extinction.