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Recent Climate Change
The global temperature of the Earth has increased over the last century.
Current temperatures are 0.90 °C over the 1950-1980 average
In fact global temperatures are now the highest in the last couple of thousands of years
2017 was the second hottest year on record
2016 was the hottest year on record (0.12 degrees above 2015).
The four hottest years (in order): 2016, 2017, 2015, 2014).
17 of the 18 warmest years have occurred since 2001.
Natural Greenhouse Effect
The above picture shows the natural greenhouse effect in red. All objects emit heat in the form of infrared (IR) radiation. Gases in the atmosphere absorb the IR radiation from the Earth and reradiate it back to the surface. This regulates the temperature.
The natural greenhouse effect allows life to survive on Earth.
But problems occur when humans cause additional greenhouse effects.
Now we can define global warming:
Major human-generated greenhouse gases :
- Carbon dioxide 76% of all greenhouse gas emissions
- Methane 16%
- Nitrous Oxide 8%
- F-gases 1%
Black carbon also contributes to global warming.
Carbon dioxide is by far the most important of the greenhouse gases, causing most of the global warming. Atmospheric concentration is about 400 ppm.
Largest sources of carbon dioxide:
- Burning of carbon-based fuels
- Deforestation and burning grasslands for crop production
Methane is at lower concentrations, but has a stronger greenhouse effect. Concentration is about 1.5 ppm, greenhouse effect is 29 times that of carbon dioxide.
Largest sources of methane:
- Agriculture (60%)
- Cattle and other ruminants
- Rice farming
- Disturbance of peatlands
- Natural wetlands and permafrost
- Leakage from natural gas pipelines, tanks, etc.
- Landfills and wastewater treatment plants
Nitrous Oxide (N20) is at low concentrations and has a strong greenhouse effect. Concentration is about 0.3 ppm, greenhouse effect is 298 times that of carbon dioxide.
Largest sources (60% natural, 40% anthropogenic):
- Natural denitrification in soils
- Breakdown of fertilizers
Fluorinated gases (F-gases) which contribute to climate change include:
- Hydrofluorocarbons (HFC's) - used as substitutes for CFC's and HCFC's (HFC's do not destroy the ozone) - these are to be phased out by 2047
- Perfluorocarbons (PFC's) - used in electronics and other industries
- Sulfur Hexaflouride (SF6) - used in high-voltage switches
Soot or Black Carbon are very fine particle of pure carbon.
Formed from incomplete combustion of carbon-based fuels (both fossil fuels and biomass).
Black carbon's effect on global warming is that, unlike most particles which reflect light, black carbon absorbs sunlight, heating it up and contributing to global warming.
Impacts of Global Warming
Changing of the weather
Global warming will cause shift in climate
An animation of how the Earth's climate would change can be found here
- Generally, more hot days and fewer cool days.
- Tropics will get less precipitation.
- Polar regions will get more precipitation.
- Temperate regions will shift north.
Extreme weather events
Extreme weather events will increase. These include:
- Heat waves
- Typhoons, hurricanes, and tropical cyclones
- Severe storms, tornados, etc.
Changing of the climate, along with extreme weather, will reduce crop yields and decrease food security.
Melting of sea ice
Sea ice is the frozen sea. Most of the Arctic Ocean, especially around the North pole is sea ice.
One of the biggest effects of global warming has been melting of sea ice, ice sheets, and glaciers due to rising temperatures.
- Unlike sea ice, ice sheets and glaciers are formed on land
- Ice sheets (>50,000 sq. km) are found in only two places: Greenland and Antarctica
The ice sheet in greenland is of the most concern. Greenland's ice sheet is 1.7 million square kilometers in area and averages 2.3 kilometers deep. It holds 7% of the world's freshwater.
Greenland has been losing ice at a rate of 286 billion tons of ice per year since about 2000.
- Glaciers are found on all continents except Australia
- Glaciers are important as sources of freshwater, many major rivers are feed by glaciers
- Many glaciers are disappearing due to melting from global warming. Some areas may lose all of their glaciers.
Sea level rise
The melting of the ice sheets and glaciers causes the amount of seawater to increase. Also heating water causes it to expand.
Models estimate that sea levels will rise 0.18 - 0.59 m. 
10 percent of world's population lives less than 10 m above sea level.
Freshwater and coastal systems
- Changing precipitation and melting snow and ice affect water quantity and quality
- Sea level rise, along with extreme weather, will cause submerging, coastal flooding, and coastal erosion
- Many small island countries are especially vulnerable. Some islands may be submerged
Global warming can also affect wildlife, including:
- Shifting geographical ranges
- Changes in seasonal activities
- Changing migration patterns
- Changing species interactions
- Increased extinction rates
Golbal warming also has impacts on social issues:
- Increased health problems (heat-related problems, infectious diseases, etc.)
- example: Malaria-carrying mosquitoes cannot live in cold climates. Already we have see malaria further north than previously
- Displacement of people
- Risk of violent conflict
- Inequalities in development may be increased
Permafrost is soil which remains frozen all year.
Melting of permafrost is a feedback mechanism. It releases methane, which increases global warming, which in turn causes more permafrost melting creating a loop.
This effect is due to the carbon dioxide directly and not temperature change.
Carbon dioxide dissolves in the ocean to create acid conditions.
This in turn has an effect on marine organisms.
Acidic conditions increase the solubility of calcium carbonate in shells of shellfish, coral, etc.
- Previously, most international agreements were based on keeping warming to 2 °C above preindustrial levels
- Under the Paris Agreement, that was changed to 1.5 °C
- Warming reached 1 °C in 2017
Methods of mitigation
- The most important methods were discussed under the Sustainable Energy section under Energy.
- Of these the most important is phasing out of fossil fuels. The Intergovernmental Panel on Climate Change (IPCC) has stated that complete phase out must be done by the year 2100 (with 80% renewable energy by 2050)[ref 1].
- carbon tax - taxing companies for each ton of carbon dioxide they produce
- carbon markets (controversial) - trading carbon emissions on an open market (like a stock market)
- Afforestation and reforestation.
- Bioenergy with carbon capture
- - Carbon capture (or sequestering) is capturing CO2 and then pumping it underground
- Soil sequestering
- Direct Air Capture
- Important to note these methods are unproven
- Reduction in amount of nitrogen fertilizers used
- Conservation agriculture (no till, agroforestry, etc.)
- Livestock management
- Changing diets (especially in amount of meat consumed)
- Ecosystem restoration
- Wetland management
- Prevention of destruction (especially drainage and fires) of peatlands
Very Controversial (and probably not achievable) methods - Geoengineering ???
- Geoengineering - mega projects to reduce effects of global warming
- examples: setting huge mirrors in outer space, adding huge quantities of iron filings to the ocean, injecting aerosols of sulfur dioxide into the stratosphere
- problems: hugely expensive, most are not technically feasible with today's technology, may have undetermined consequences, and questions about governance
- note most of these do not address ocean acidification
- Building sea walls
- Changing crop types
- Generating a fund to help low income countries (the most talked about adaptation measure)
- Note that CFC's are often given, but due to the Montreal Protocol they now account for less than 0.1% of all emissions
- A recent article has indicated that these models may under estimate the rise by a factor of 2. See http://iopscience.iop.org/1748-9326/7/4/044035/article