Effects on the Hydrosphere & Atmosphere (DP IB Geography)

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

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

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