Spec S2 Flashcards
1
Q
What is the evidence for global warming since the late-19th century?
A
- Increases in global temperatures
- Shrinking valley glaciers and ice sheets
- Rising sea levels
- Decreasing snow cover and sea ice cover
- Increasing atmospheric water vapour
- Extreme events
2
Q
Increases in global temperature
A
- 1880 start of accurate records of global and ocean temperature
- Overall trend has been temperature rise, however there have been anomalies, eg. June temperatures between 1880-1937 below 20th century average
- 2015 was the 39th consecutive year of an increase in annual global temperature rise above average
- 10 warmest years on record have occurred since 2000
- Global average temperature as of 2023 - 1.48 degrees higher than 1880
3
Q
Shrinking valley glaciers and ice sheets
A
- Predicted that in the Alps, valley glaciers may shrink by 80-96% by the end of the century
- Trift Glacier in Bernese Alps of Switzerland example of retreat since 1998
- In 2000 a new glacier lake began to form at its snout, there was a very rapid growth of the lake between 2002-2003
- In summer 2003 there were very high melt rates in the Swiss alps with losses of more than 2m thickness
- By 2007 the glacier was no longer in contact with the lake and by 2008 it had retreated 1100m since 2000
- In 1850, 150 glaciers were observed in Glacier National Park Montana, same in 1910, however by 2010 only 25 glaciers were observed
- Between 1961 and 2005 the thickness of small glaciers worldwide decreased by 12m on average
- 97% of the global ice store is in the Antarctic and Greenland ice sheets, whilst it would take centuries for the polar ice sheets to disappear, at current rates of melting, they are still shrinking fast
- Every year, polar ice melting is contributing 1mm to sea level, with losses due to: melting of ice surface due to warming atmosphere, warming producing meltwater penetrating the ice and increasing velocity of glacier flow, warming of oceans means melting of ice sheets in coastal areas (Larsen B ice shelf in Antarctica broke up in less than a month in 2002)
4
Q
Rising sea levels
A
- Sea level rise can be attributed to thermal expansion (expansion of sea water as it warms) and added water from melting land ice
- Since 1900 the average rise was 1.0-2.5mm/yr, but current rate of change is 3.4mm/yr
5
Q
Decreasing snow cover and sea ice
A
Snow cover
- Most of the earth’s polar regions are covered by snow and ice most of the year, but at lower latitudes season and elevation will determine snow cover
- Spring snow cover has declined by 2% per decade since 1966 in the northern hemisphere
- Snow has high albedo (reflects 70-80%) of incoming solar radiation
- Witha decrease in snow cover there is an increase in absorption of solar radiation and air temperatures rise, which results in positive feedback with further increase of warming as even less snow cover
Sea ice
- Frozen sea water floating on ocean surface only forms in polar regions and forms and melts with the seasons
- In the winter, Arctic sea ice may cover 17-20 million km^2 (average), shrinking 4-6 million km^2 in summer
- Since 1979, Arctic sea ice has significantly decreased both in extent and thickness, in September 2012, the area of Arctic sea ice shrank to a new minimum of 3.63 million km^2
- Less sea ice results in more solar energy being absorbed by the sea surface, raising air temperatures and causing more rapid melting
- Antarctica however has defied this trend, with an expansion of just over 1% per decade, however this was far below scientists predictions
6
Q
Increasing atmospheric water vapour
A
- Scientists suggest that water vapour has a heat-amplifying effect potential enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere, and as such is the most important greenhouse gas
- Water vapour traps huge amounts of energy radiated from the earth’s surface creating a natural greenhouse effect
- The amount of water vapour in the atmosphere is related to temperature and rates of evaporation so in a warmer world, there will be more atmospheric moisture
- Therefore, there is a positive feedback loop with warming and waste absorption increase in a spiralling cycle, increased water vapour leads to warmer temperatures, increasing evaporation, resulting in more water vapour, hence more warming, etc
7
Q
Extreme events
A
- Since 1950, the number of record high temperature events in the US has increased whilst the number of record low temperature events has decreased
- Both the US and the UK have also experienced more intense rainfall events
- Between 2011-2013, the US experienced 32 weather events that cost at least 1 billion dollars in damages
- There have been more intense and frequent heat waves, less frequent intense cold waves, regional changes in floods, droughts and wildfires - all things expected with a warming planet
8
Q
Why have anthropogenic greenhouse gas emissions increased since the pre-industrial era?
A
- Huge surge in demand for energy due to industrialisation and technological advances (particularly in manufacturing and transport)
- Massive global population growth, from 1 billion in 1800 to 7.4 billion in 2015 + rising living standards
- Land use change, especially deforestation and the draining of wetlands for food production and urban development
9
Q
Demand for energy
A
- Since first industrial revolution in 19th century, world has heavily relied on energy from fossil fuels, despite developments in renewables, fossil fuels still supply 87% of the world’s energy
- Around 2/3 of global anthropogenic GHG emissions comes from burning of fossil fuels, which release 10 billion tonnes of CO2 annually
- Since 1750, cumulative anthropogenic CO2 emissions totally 2000GT, 3/4 of these emissions are from burning fossil fuels
- Since mid 20th century, demand for fossil fuels has grown hugely, expansion of the world economy between 1990 and 2012 (stimulated by globalisation and the growth of EDCs) increased the consumption of fossil fuels and according to the International Energy Agency, led to a 51% increase in CO2 emissions
- Although coal is no longer the leading fossil fuel, coal production in the early 1st century reached record levels - two of world’s largest economies, China and India, are powered largely by coal
- Coal emits nearly twice as much CO2 as natural gas and 20% more than oil
10
Q
Land use changes
A
- Around 1/3 of GHG emissions comes from land-use changes and the emission of carbon from deforestation, drained wetlands and cultivated soils
- These processes transfer carbon from the biosphere to the atmosphere
- 40% of planet’s land surface used for agriculture today vs 7% in 1700
- 15-25% of global forests lost since 1700, only 31% of land surface today clothed by forests
- Deforestation, mostly in the tropics and sub-tropics, continues apace, with 5.2 million ha cleared between 2000 and 2010
11
Q
Changing balance of anthropogenic emissions around the world
A
- Most CO2 and other GHG emissions 1850-60. originated from industrialised economies of North America and Europe
- Historically USA has dominated CO2 emissions, its emissions since 1850 (28%) are almost equal to the combined emissions of China, Russia, Germany and the UK
- Since 1960, regions shifts have occurred in emissions of CO2 and other GHGs
- Asia’s emissions increased massively, North American and Europe stabilised, in case of Germany and UK emissions have declined
- Early in 21st century, China’s reliance on coal and explosive economic growth meant that they overtook the USA as the world’s leading emitter of CO2
- Per capita - ACs such as USA, Australia, Germany and UK all ahead of EDCs (China and India), eg. USA and Austria emit average of 17 tonnes/ year-1 per person of CO2 vs 5.4 tonnes by China and 1.4 tones by India
- Global emissions remain highly uneven, top 10 CO2 emitting countries account for nearly 80% of all emissions
- When emissions of other GHGs such as CH4 from land use changes are added to CO2 from fossil fuel combustion, slightly different regional picture emerges - China and USA still first, Brazil and Indonesia third and fourth - due to large-scale deforestation in Amazonia and Indo-Malaysia
12
Q
Enhanced greenhouse effect
A
- Natural greenhouse effect raises average global temperate by around 15 degrees celsius
- 1/3 increase in CO2 since early 19th century, from 280 ppm in 1800 to 424 ppm today, has created an enhanced greenhouse effect
- As Earth’s climate has warmed, change has been amplified by increases in evaporation and therefore atmospheric water vapour and the melting of permafrost in the Arctic releasing CH4 and CO2
- Enhanced greenhouse effect increases absorption of long-wave radiation in the atmosphere and raises global temperatures
- Trend is consistent with the history of climate change over past 1 million years, which shows that warming is associated with unusually high concentrations of GHGs in the atmosphere
13
Q
Impact of human activity on mean global energy balance
A
- Earth and atmosphere system is a closed system, inputs of solar radiation and outputs of terrestrial radiation
- Only 45% of incoming solar radiation at the top of the atmosphere reaches and warms the Earth’s surface
- Small amount of insulation is reflected from surfaces such as snow and ice, 1/3 reflected from clouds and 1/5 absorbed by water droplets, ozone, CO2 and dust in the atmosphere
- 2/3 of outgoing, long-wave radiation from Earth’s surface is lost to space, rest is absorbed by GHGs (especially water vapour, CO2 and CH4)
- Energy also exported from surface to the atmosphere by convection currents or thermals and by latent heat, released when water vapour cools and condenses
- 84% of all heat energy leaving Earth’s surface returns as back radiation
- Human activity in past 200 years through consumption of fossil fuels and land-use change has disrupted this delicate balance
- Increasing concentrations of GHGs absorb larger proportion of terrestrial radiation, returned to the surface as back radiation, increasing average global temperatures
- Rising global temperatures increase evaporation, transfer more latent heat to the atmosphere and increase concentrations of water vapour, the most important GHG
- Rising global temperatures melt snow, glaciers and sea ice in the Arctic, reducing albedo and the reflection of incoming solar radiation adding heat energy to the Earth-atmosphere system
- Deforestation so reduces albedos, increasing absorption and the warming effect
