“Scientific theories are models of reality constructed by human beings, and these models inevitably reflect, and are used to endorse, the values and interests of those who create them.”

				Peter Bowler

 Global Climate Change 3

•	We have added substantial amounts of greenhouse gases to the atmosphere
•	These gases are contributing to global warming
•	Environmental Forcing Factors - EFF’s - factors that are responsible for climate forcing, like greenhouse gases

•	Greenhouse gases are partly natural…
•	Relative contribution of human activities:
>	Carbon Dioxide 50 - 60%
>	Methane 12 - 20%
>	Nitrous oxide 5%

•	Residence time of greenhouse gases is as important as their relative warming effect
•	Residence time is the time that greenhouse gases remain in the atmosphere (also called removal time)

•	Thousands of gases have the ability to absorb and retain atmospheric infrared radiation, including water vapor
•	Any and all of these gases are potential greenhouse gases

•	Ozone acts as a greenhouse gas, but the ozone layer has stayed constant for millennia (now declining)
•	Tropospheric ozone, on the other hand, could be a serious problem
•	Lower-level ozone due to cars, power plants, burning of biomass

•	Ozone depletion is indirectly reinforced by global warming
•	Increased CO2 increases formation of “polar stratospheric clouds”, which tend to increase rate of ozone destruction

•	Only a handful of greenhouse gases remain in the atmosphere long enough to cause a serious problem
•	Carbon dioxide, nitrous oxide, CFC’s, have the longest residence times

•	Methane and carbon dioxide produce the strongest climate forcing
•	Methane only stays in the air for ~ 10 years, CO2 will be around for a century or more

•	
Aerosols consist of very fine particles suspended in a gas
•	Aerosol clouds are highly reflective
•	Can be sulfate aerosols (light clouds), dust, organic aerosols (light clouds) or black soot aerosols (dark clouds)

•	Both sulfate aerosols and black-soot aerosols have a relatively low residence time in the atmosphere
•	Gone in about 10 days…
•	Sulfate aerosols have a negative forcing!

•	Sulfate aerosols come from natural and anthropogenic sources
•	Sulfate aerosols - natural sources
>	Volcanic outgassing
>	Marine organisms - sulfur aerosols
>	Vegetation - organic aerosols

•	Sulfate aerosols - anthropogenic sources
>	Coal-fired power plants
>	Coal-fired industrial plants

•	Sulfate aerosols reflect light & heat back into space, reduce global temperatures
•	Ironically, by cleaning up plant emissions, using higher grades of coal with lower sulfur content, we are contributing to global warming!

•	Marine plankton emit sulfur aerosols
•	Plankton give off dimethyl sulfide, DMS (small amounts, but lots of plankton)
•	Oxidized into SO2 in the atmosphere
•	About 50% of sulfur aerosols are due to biogenic sulfur emissions

•	Vegetation produces organic aerosols
•	Plants give off organic molecules that accumulate, form a cloudy haze
•	Smoky Mountains are smoky because of organic aerosols, though smokier today due to pollution

•	Volcanic aerosols can have a significant effect on climate, despite their short residence time - why??
>	Repeated eruptions on a large scale release tremendous amounts of dust
>	Much of the dust settles out in 1-2 years, but finer particles form aerosols that reflect rays back into space for 10 years

•	1816 was the year without a summer
•	Series of volcanic eruptions, culminating in 1815 with the eruption of Mount Tambora in Southeast Asia, most spectacular eruption in 15,000 years!
•	Dumped vast amounts of dust aerosol into the air, reflected solar energy into space

•	Freeze in early June nipped flowers, crops in the bud, frost continued until June 11th, with heavy snowfall
•	July 6-9, another frost hits New England, August 13-14 still more frost!
•	Widespread crop failures, high food prices, in US and Europe

•	Black soot aerosols absorb heat, directly contribute to global warming
•	Formed by incomplete combustion of fossil fuels, biomass (ex. forest fires)
•	Black aerosol clouds absorb heat directly, reduce reflection of heat back into space

•	2013 Journal of Geophysical Research almost triples the previous estimate of contribution of black soot aerosols to global warming
•	Only saving grace is short residency time
•	Easier to clean up, immediate effect on climate 

•	A large part of the uncertainty surrounding the effects of aerosols concerns their role in cloud formation
•	Clouds reflect suns rays back into space, reduce global warming

•	Tiny particles in aerosols form nuclei for water vapor to condense into clouds
•	More tiny nuclei from aerosols means smaller water droplets in clouds

•	Smaller droplets increase total surface area for reflection - Twomey Effect 
•	Think of one large reflective sphere versus a dozen smaller reflective spheres

•	Smaller droplets, get brighter, more reflective clouds
•	Smaller droplets also tend to inhibit rainfall, so clouds last longer, more reflectivity

•	Clouds are a very important variable in global warming
•	Clouds are the least understood part of global warming, source of uncertainty in climate models

•	Have greenhouse gases actually altered the temperature of the Earth?
•	Recent surge in severe storms suggests a causal link, but controversial
•	NOAA scientists claim that a short term natural cycle, the Atlantic multidecadal signal, is to blame

•	Atlantic multidecadal signal is poorly understood, seems to be linked to 
>	Increased ocean temperatures
>	Heavier rainfall in West Africa
>	Drier conditions in the Amazon

•	1880’s, 1890’s were severe hurricane seasons, well before the Industrial Revolution led to increased CO2 levels…
•	1970-1995 was a relatively quiet period in this cycle
•	Current phase of strong hurricanes could last another 30 years

•	Two controversial studies in 2005, from Georgia Tech (Judith Curry) and MIT (Kerry Emmanuel)
•	Both claim to detect a significant spike in hurricane intensity above the expected pattern
•	Both attribute it to global warming

•	20th Century - global mean surface air temperatures (average temps at ground level) increased 0.4o - 0.8o C ( 0.7o - 1.5o F)
•	Ocean temperatures increased by 0.05o C (0.09o F), measured down to 10,000 feet
•	Most of this global warming occurred in the last 20 years

•	Carbon dioxide is the single most important factor in global warming
•	Atmospheric carbon dioxide levels closely match temperature changes

•	Raises a philosophical question, often posed by critics of global warming
•	Correlation does not equal causation
•	Could be many other factors correlated with temperature change, doesn’t mean they caused it…
•	For instance…

•	Argument has merit as an epistemological theory – well known logical fallacy
•	Accept it completely, however, only real science left is physics and engineering…
•	Most natural science and social science is based on statistical analysis

•	Correlation does not prove causation, but it implies it, gives us a place to look for a more direct connection
•	Can’t really experiment on the Earth…
•	In the case of global warming, many lines of circumstantial evidence point to the same set of hypotheses, pretty strong case

•	Can never completely rule out an alternative explanation
•	But as more and more such explanations are tested and eliminated, connection becomes more and more likely

•	The real mystery is not whether CO2 raises global temperatures…
•	Mystery is why temperatures aren’t even higher than they are
•	Amount of CO2 released in the 20th Century should have caused twice as much temperature increase as observed

•	Where did all the carbon go?
•	Must be a large carbon sink in the ocean or biosphere that we have somehow failed to account for…

•	How hot will it get?
•	Answer varies from model to model…
•	By the end of the 21st Century, range of predictions by models of ~ 1.4o C - 5.8o C (2.5o F - 10.4o F)

•	Models predict greater warming over higher latitudes, especially in winter and spring
•	Relatively greater temperature increases on land than in the sea

•	Not so bad…What’s a mere 5o C?
•	Equals the temperature difference between today and the last Ice Age!!
•	Most ecosystems would be greatly affected by an increase of only a few degrees

•	As of 2006, now within one degree of the highest global temperature in the last 1 million years!
•	2-3 degrees more, will match high mark set in the Pliocene (3 mya), when sea levels were 80 feet higher than today… 

•	Arctic seal populations declining, replaced by species adapted to warmer waters
•	Number of polar bear babies, and average weight of polar bears have declined ~15% over the past 25 years
•	Polar bears could be extinct by the end of the century!

•	Tropics are actually expanding – now 2o - 4.8o latitude closer to the poles!
•	Also means the arid belt that borders the tropics is moving farther North and South
•	American Southwest may become the new Sahara

•	Effects of global warming
>	Natural ranges of plants and animals would change
>	Shifts in populations of many plants and animals to higher elevations or higher latitudes
>	Species that could not disperse or migrate quickly enough (snails, trees…) might go extinct

•	Effects of global warming
>	Migratory birds are already showing signs of change
>	20 species now arrive ~21 days earlier
>	7 species of warblers have shown range shifts averaging 65 miles farther north in the past 24 years, none have shifted farther south

•	Flycatchers that migrate from Africa to the Netherlands arrive at the same time as 20 years ago
•	But the moths they rely upon to feed their nestlings now peak two weeks earlier
•	Lots of hungry baby birds…

•	Effects of global warming
>	1,700 species of plants animals, insects are currently moving north, rate of 4 miles per decade from 1950-2000 (Nature 2006)

•	Effects of global warming
>	Entire global pattern of agriculture would change
>	US Midwest would be cooler, better grain temps in Canada and Russia - boreal soils not well suited to farming (acidic)

•	
Effects of global warming
>	Greenland 2007 started harvesting potatoes, cauliflower, cabbage, other veggies for the first time in history
>	Average temps up two degrees since 1990
>	Cod starting to return to coastal fisheries

•	Effects of global warming
>	Fewer cold snaps in the temperate zone
>	More droughts, more severe droughts

•	Effects of global warming
>	More water vapor in the air (higher temps increase rate of evaporation
>	Balanced by more intense rainfall events
>	Increase in number and severity of tropical storms, hurricanes, monsoons, which rely on heat energy

•	1995 - Highest temperatures ever recorded in the Atlantic Ocean
•	Same year, 19 tropical storms, double the previous 50-year average!
•	21” of rain in New Orleans!!

•	1990’s were the warmest decade of the past millennium
•	1995-1999 broke the all-time record, 65 tropical storms (41 hurricanes, 20 were major hurricanes)

•	2004 UK Hadley Center report claims likelihood of extreme heat waves in Europe have doubled
•	Odds of a killer heat wave like the one in 2003 will rise to every other year by 2040

•	Average night temps also increasing, so no more relief at night from the heat
•	2006 study from US National Climatic Data Center shows record US streak of high night time temps over the past 8 years
•	2006 study in Journal of Geophysical Research says trend is global

•	Most recent international report comes from the UN’s IPCC (Intergovernmental Panel on Climate Change)
•	Result of several years of study by a highly respected panel of scientists and policy makers from several nations

•	Followed in May 2008 by US Climate Change Science Program Report
•	First official admission by the federal government that global warming is a real problem

•	Both reports present a strong case that global warming is ongoing, and that we are the ones responsible for the change in climate 
•	Reports are available on BB, links to both are on my enviro links page…

•	Reports conclude that global warming is ongoing and getting worse
>	Increased average air and water temperatures
>	Widespread melting of ice and snow
>	Rise in average global sea levels

•	IPCC concludes that current warming exceeds any similar natural trends over the past several thousand years
•	Change is due to human activities since 1750, including fossil fuel combustion, changes in land use, and agriculture

•	Effects of global warming
>	Because CO2 is only 0.03% of the atmosphere, CO2 limits plant growth
>	CO2 fertilization - add CO2, get lush plant growth
>	But usually get plant tissues that are lower in nutrients - harder for herbivores to feed

•	Effects of global warming
>	Longer growing season in some areas
>	Earlier Spring flowering for many species
>	Increased water efficiency in plants
>	Changes in distribution, range of species
>	Increased rates of extinction

•	Effects of global warming
>	Evolutionary changes will occur as species try to adapt to the changing climate
>	Recent study of mosquitoes who live in pitcher plants in Oregon, bug is delaying breeding and development time until later in the season, when other species are preparing to hibernate

•	Effects of global warming
>	Coral reefs subject to bleaching by higher temperatures in shallow water
>	1998 alone, 16% of the world’s remaining reefs were bleached or dead from global warming
>	Increased acidity of the oceans due to more dissolved carbon dioxide (carbonic acid)
>	Increase of 30% in acidity since Industrial Revolution
>	Affects shell development, shell weights, threatens coral reef integrity 

•	Effects of global warming
>	Public health problems - more tropical disease vectors (carriers) move north (mosquitoes)
>	West Nile virus now regular in Jefferson Parish
>	Encephalitis increasingly common

•	Effects of global warming
>	Increased melting of snow and ice, glaciers retreating, polar ice caps thinning
>	Increased input of fresh water into seas
>	Rise in sea level - already underway, ~ 2 mm per year

•	Sea level rises for two reasons
>	Ice and snow melt causes direct increase
>	Increasing temperature of water expands volume of water = thermal expansion
•	Polar ice caps are the joker in the deck - potential to increase sea level 25 feet!!

•	Estimated 1/2 meter to 1 meter rise in sea level over the next 100 years
>	Loss of 82% of our coastal wetlands
>	Flood all three NYC airports
>	Flood the NYC subway system
•	Economic cost to US of ~ $1 trillion!!

•	Effects of global warming
>	American West water supply will be threatened
>	Depends on amount and timing of Spring runoff from mountains
>	Reduced snow cover = reduced water supply

•	Models of climate change are far from perfect
•	But all current models make the same general prediction - our planet is heating up 
•	Most scientists disagree about the timing and degree of global warming, not its reality

•	Ironically, one of the effects could be to trigger the next Ice Age!
•	Recent improvements in precision of data suggest that very warm or very cold climate changes can occur in relatively brief period
•	Maybe as little as ten years…

•	Studies of Greenland ice sheet cores and deep-sea sediment cores suggest significant climate shifts can occur in 10-20 years!
•	Theory centers on the oceanic conveyor belt
•	Ocean currents redistribute equatorial heat, help drive weather systems

•	Oceanic conveyor belt is the global pattern of major currents that redistribute tropical heat from the equator to the poles

•	Changes in the temperature and salinity of the oceans change the way that heat is redistributed - especially in the Atlantic
•	These changes cause the planet to quickly shift to a climate that is much warmer or much colder

•	Not a new idea – proposed in 1875 by James C. Roll (Climate and Time)
•	Proposed that long term orbital cycles would lead to series of cold winters

•	Would alter surface winds that drive the Gulf Stream, shut it off, lead to an ice age
•	Modern version relies on a different mechanism
•	Changes in sea surface temps and salinity

•	
Three stable patterns of global climate:
>	Warm pattern - current situation
>	Cold pattern
>	Coldest pattern - extensive glaciation
•	Driven by changes in water temperature and salinity in the oceans

•	Cold water is denser, heavier, than warm water (just like air)
•	Cold water tends to sink, warm water tends to rise 

•	Water heated in the tropics is pulled toward the colder poles
•	As it moves north, it becomes cooler, gives off heat to the surrounding air or land
•	Also evaporates, becomes saltier - saltier water is also heavier than fresh

•	Cooler, saltier water is denser, sinks to the bottom, pulls warmer water from the tropics to replace it 
•	Resulting warm current heats the coast of North America and Europe

•	During warm periods (like today), there are two vast areas of the North Atlantic where heavier cold water is sinking to the bottom of the ocean

•	Sinking cold water moves along the ocean floor, wells back up in the North Pacific, completes the overall loop of the primary planetary ocean currents

•	Why should I care about any of this ??

•	Ocean currents are what make it possible for us to live outside of the tropics
•	Without the Gulf Stream, ex., the eastern US would be a very frigid place to live

•	During colder periods, there’s only one area of the North Atlantic where heavier cold water is sinking to the bottom of the ocean
•	Less heat is conveyed from the tropics to the temperate zone
•	Much colder temperatures, but not as cold as an ice age

•	During coldest periods (like Ice Age), there are no areas of the North Atlantic where heavier cold water is sinking to the bottom of the ocean
•	Something happens to completely shut down the oceanic conveyor belt, causing an Ice Age

•	How does this relate to global warming?
•	Increased melting of ice and snow feeds large amounts of fresh water to the oceans, which become less salty
•	Surface waters not heavy enough to sink, slows down or shuts off conveyor belt

•	Remember the Younger Dryas? 
•	Climate aberration ~12,000 ya, lasted 1,000 years, return of glaciers to Europe
•	Probably caused by draining of a huge glacial lake, Lake Agassiz, when glaciers melted after the last ice age

•	~ 8,200 years ago, melting of Canadian glaciers caused similar climate aberration
•	Harsh cold snap that lasted ~ 400 years
•	Influx of fresh water into the oceans caused by global warming could bring on an extended cold spell, even an ice age!

•	May explain the Little Ice Age…
•	Melting ice and snow during the Medieval Warm Period might have partially shut down the conveyor belt
•	Middle “colder” state of Taylor’s model…

•	If the model is correct, we could experience a severe climatic shift in as little as 20 years
•	The Day After Tomorrow exaggerates the time frame, but the basic science is sound!

•	Recent Nature report (Bryden et al. 2005), northern European currents have slowed down 30% in the past 50 years
•	May signal the beginning of a major climate shift – some controversy…
•	Attributed to increased Arctic and glacial ice melt, decreasing density of seawater

•	So what can we do to minimize the effects of global warming?
>	Cut way back on fossil fuel emissions, especially carbon dioxide
>	Rely more on natural gas, less on coal

•	So what can we do to minimize the effects of global warming?
>	Develop alternative energy sources
>	Stop burning tropical forests
>	Pray….