Effects on the Hydrosphere & Atmosphere (DP IB Geography)
Revision Note
Water Stores
The increase in mean global temperature has wide-ranging effects, including melting ice caps and glaciers, shifts in precipitation patterns, and changes in ecosystem dynamics
The higher concentration of greenhouse gases are contributing to the intensification of extreme weather events such as hurricanes, droughts, heatwaves, and heavy rainfall
Long-term changes in climate and weather patterns occur as a result of the altered energy balance in the Earth's atmosphere and oceans
Rising greenhouse gas levels also contribute to the thermal expansion of seawater and the melting of land-based ice, resulting in sea level rise
Effects on water stores
The hydrological cycle involves the exchange of energy, which leads to temperature changes
As water evaporates, energy is taken from its surroundings which cools the environment
When it condenses, it releases energy and warms the environment, this exchange of energy influences the local climate
Changes in temperatures have reduced polar ice and the albedo effect
Ice melt in the polar region releases fresh water into the oceans and this changes the thermohaline pattern
This circulation pattern relies on heavy salt water to transport water, carbon and heat around the globe
Large deposits of freshwater into the oceans will disturb the ocean conveyor belt
This has the potential of stalling or reversing the ocean circulation pattern
Dark oceans absorb more heat, which increases evaporation into the atmosphere - a positive feedback loop
However, increased evaporation also increases cloud formation, which radiates insolation back out of the atmosphere which creates a cooling effect - negative feedback
The higher the temperature, the higher the volume of water in the atmosphere, which leads to more precipitation
This is because the atmosphere can retain more moisture with higher temperatures
Changes in water availability
Global warming can lead to alterations in precipitation patterns, resulting in changes in water availability
Some regions may experience increased rainfall and flooding, while others may face more frequent and severe droughts, impacting water resources for agriculture, drinking water, and ecosystems
Sea-level change
Changes in the amount of sea ice, lead to a greater volume of water in the ocean basins, as a result of thermal expansion
Thermal expansion occurs as water warms, and the warmer fluids expand to take up a greater volume
During the last Ice Age, sea levels fell as water was locked in glaciers and ice sheets, rising again as the ice melted, creating waterways such as the English Channel
Greenland and Antarctica lost 6.4 trillion tones of ice between 1992 and 2017, causing global sea levels to rise by 17.8mm
Today, ice sheets contribute to about a third of all sea-level rise, whereas in the 1990s, their contribution was just 5%
By 2100, polar temperatures could be as high as 7°C above pre-industrial levels
Sea levels are linked to global warming and will have a significant effect on many low-lying coasts and islands
Many Pacific Ocean islands, such as Kiribati and Tuvalu are at risk of being completely submerged by rising sea levels
Coastal flooding
Rising sea levels, attributed to climate change, can lead to coastal flooding and increased vulnerability to storm surges
This can result in the loss of land, infrastructure, and the displacement of coastal communities
This issue is made worse as many of the world's densely populated areas are located on coastal lowlands
New York and Miami in the US are major cities vulnerable to sea-level rise as the cities are built at sea level
Bangladesh is an extensive delta, where the river Ganges discharges into the Bay of Bengal. The delta, largely covered with a swamp forest, is one of the world's most densely populated countries and is particularly vulnerable to global warming and sea level rise
Examiner Tip
Ice melting in a glass of water does not change the density of the water, because they are both fresh water.
However, an iceberg (freshwater) melting in the ocean decreases the density of the salt water, and this raises the sea level very slightly.
Carbon Stores
Carbon stored in ice
Permafrost acts as a carbon sink by storing partially decomposed plant and animal matter
Melting of the permafrost triggers methane release into the atmosphere, as the plant and animal matter begin to decompose
Methane is a more potent greenhouse gas than CO2 and acts as a positive feedback loop
Currently, there are approximately 5 gigatons of methane in the atmosphere
It is estimated that the Arctic permafrost holds hundreds of gigatons of methane
Polar ice sheets and glaciers are also stores of carbon
As global temperatures increase, these ice sheets and glaciers melt and release stored CO2 back into the atmosphere
Impact of ice change
Increasing temperatures are causing the melting of ice in polar regions, mountain summits, the ocean and other inland areas with ice
For example, glaciers in the Himalayas, Southern Alps, Rockies and the summits of Mt. Kilimanjaro are melting rapidly
It releases fresh water for millions of people living along the rivers in the low-lying areas of these mountains
Ocean acidification
Oceans can absorb more carbon than it emits and are important in regulating the atmosphere
It is a two-way relationship with carbon being moved both downwards and upwards through the oceans
Phytoplankton in the ocean use dissolved CO2 for photosynthesis
This transports carbon from the oceans' surface to the deeper levels for storage
As biological organisms die, their bodies sink and release CO2 into the deep water stores
Some material sinks to the ocean floor and is transformed into rocks such as limestone
This process locks up carbon in the long-term carbon cycle and prevents an easy return to the ocean surface and back into the atmosphere
However, increasing levels of carbon dioxide in the atmosphere lead to higher levels of CO2 absorption by the oceans, resulting in ocean acidification
This can have detrimental effects on marine life, including coral reefs, shellfish, and other organisms that rely on calcium carbonate for their shells and skeletons
Carbon in the biosphere
The biosphere is also a large carbon sink
CO2 is naturally released into the atmosphere through respiration and decaying organic matter
However, human activities have released extra amounts of CO2 into the atmosphere
Plants, forests and soils have absorbed about 25% of this human-released CO2 through photosynthesis
Whilst an increase in the amount of CO2 in the atmosphere promotes improved growth of plants and carbon storage, eventually, too much CO2 and increased temperatures will have a detrimental effect on crop yields
Furthermore, deforestation has resulted in CO2 being released into the atmosphere
Water cycle/carbon cycle feedback loop
Water has the ability to absorb and transfer carbon and oceans absorb 33% of CO2 emitted to the atmosphere
The bulk of human-generated CO2 has been absorbed by oceans, although this rate of absorption is slowing down
As ice sheets melt, carbon storage increases, although this process cannot continue indefinitely, as eventually, the pH levels of the oceans will drop creating higher levels of ocean acidification
Warmer temperatures increase marine phytoplankton populations to a point
Phytoplankton release dimethylsulphide (DMS) leading to increased cloud formation and cloud cover
Insolation is reduced to the oceans, reducing temperatures, reducing phytoplankton activity, which will lessen cloud cover over the oceans
With rising ocean temperatures; photosynthesis is reduced, as phytoplankton prefer cooler waters
Also, increasing ocean acidity means molluscs and shell-forming marine creatures are finding it difficult to extract bicarbonate ions needed to convert into calcium carbonate, which reduces their ability to be a carbon reservoir
Examiner Tip
Note that while ocean acidification shares the same cause as global warming (increased atmospheric carbon dioxide), it is not a direct result of global warming.
Extreme Weather Events
Changes in climate patterns are likely to increase the frequency and severity of weather events
Since the 1980s there has been an increase in extreme weather events
Particularly floods, storms and extreme temperatures
The Atlantic hurricane season runs from 1 June to 30 November
This is when tropical storms are most likely to form in the North Atlantic Ocean
On average, 14 named storms occur each season, with an average of 6 becoming hurricanes (Cat 3) and 3 becoming major hurricanes (Cat 4+)
2021 produced 21 named storms (winds of 62+ km/h), including 7 hurricanes (winds of 119+ km/h) of which 4 were major hurricanes (winds of 178+ km/h)
This was the 6th consecutive above normal season
The frequency and length of droughts are increasing
Droughts are an extended period of time when there is below average rainfall
It varies from place to place and has a negative effect on vegetation, animals, and people
Water supplies such as lakes, aquifers and rivers become depleted as people continue to abstract water during a drought
Droughts are often accompanied by high temperatures, which increases the rate of evaporation, depleting water supplies faster
Length of a drought varies from place to place:
UK suffered a drought for 16 months between 1975 and 1976
In any given year, 14% of the USA is in a drought
Horn of Africa is experiencing its worst drought in 40 years
Changes in atmospheric circulation can reduce the amount of precipitation to an area
An El Niño cycle will bring droughts to Indonesia and Australia
Annual monsoon rains can fail - India relies on the monsoon rains for water
High pressure weather systems bring high temperatures which increases evaporation rates, but also block weather depressions of rain bearing clouds
A heat wave is when temperatures are much higher than the average for a long period of time, in the UK that usually means 3 consecutive days
The conditions of a heat wave varies from place to place - Spain has much higher temperatures than the UK
The Heat Wave of August 2018 became one of the hottest years since records began in 1960, reaching temperatures of 38.5°C in some parts of the UK
Extreme cold events such as the '2018 Beast from the East' storm
Began in January 2018 when the stratosphere suddenly warmed
This generated a large rise in air temperature of around 50°C in an area approximately 29km above the Earth at the North Pole
This sudden warming weakened the jet stream (which usually brings in the warmer air) and allowed the cold air from western Russia to 'flood' over Europe
Projected impacts of rising temperatures
Examiner Tip
Remember that extreme weather events are dependent on temperature increases and therefore, each event will be worse with each degree C rise. Long-term changes are difficult to predict as we do not know the final temperature that our world will ultimately reach.
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