Effects of Climate change (College Board AP® Environmental Science) : Study Guide

Effects of climate change

Glacier and Arctic ice decline 

• Glaciers reducing in size and melting ice: Arctic Sea ice is at an all-time low

• Most glaciers around the world have shrunk since 1850

• Mountain glaciers are an important source of water for many people

  • Glacial retreat in the Andes threatens water supplies of up to 50 million people

  • A large glacial loss in the Himalayas could affect millions of people living in China and India

  • Glaciers are important for the tourist industry

Rising sea levels

• Melting ice adds more water

• Warm water expands in volume (thermal expansion)

• Sea levels have risen approximately 23 cm since 1880

• Sea levels are forecast to increase a further 30 cm by 2050

• By 2100, global sea levels are predicted to rise between 0.3 and 2 metres

• Low-lying coastal areas and islands are at higher risk of flooding and will lead to displacement of large numbers of people

  • Some residents of Kiribati, South Pacific, have already abandoned their homes and claiming environmental refugee status 

  • The UN’s refugee agency estimates that 1.2 billion people could be displaced globally by 2050 due to climate change and natural disasters

  • Moving settlements or improving flood defences will be costly

• Beach erosion will increase, leading to greater coastal erosion 

• Coastal ecosystems, including coral reefs and mangrove swamps, will be lost

• Saltwater ingress is contaminating freshwater supplies and affecting coastal agriculture

Wildlife

• Plant and tree flowering patterns are changing

• Bird migration times have altered

• Shorter hibernations

• Bird nesting occurring earlier

Extreme weather events

• Since the 1980s, there has been an increase in extreme weather events:

  • Particularly floods, storms and extreme temperatures

  • The frequency and length of droughts are increasing

  • Dry conditions lead to an increased risk of wildfires

  • Rising sea levels, together with increased storms, lead to increased flooding risk

Effects of climate change on marine ecosystems

• The effects of climate change on marine ecosystems are

  • changes in sea levels

  • rising ocean temperatures

  • acidification

  • changes in ocean currents

• Some of these effects have positive impacts, such as newly created habitats on now-flooded continental shelves

• However, positive effects are often local in nature and are limited by the adaptive capabilities of marine species to adjust fast enough to survive

• Overall, the negative effects of climate change outweigh the positives, as their effects are wider reaching, such as deeper communities no longer being in the photic zone of seawater

• These changes have a cascading and lasting impact on marine biodiversity, coastal communities and beyond

  • Approximately 680 million people live in low-lying coastal areas

  • Nearly 2 billion in half of the world's megacities are coastal

  • 3.3 billion people depend on fish for protein

  • 60 million people work in fisheries and aquaculture

Positive effects

• Increase productivity

  • In some places, warmer seas can cause more phytoplankton to grow

  • Phytoplankton is the foundation of the marine food web, so more fish might live in those places

• Species migration to colder latitudes

  • As water temperatures change, marine species might migrate to new places (particularly towards the poles where waters are currently cooler) where they can find better conditions

  • This could change the way ecosystems work and disrupt food chains

• Carbon sequestration by coastal ecosystem

  • As mangroves and seagrass beds are important carbon sinks, higher CO₂ levels could help these coastal environments grow

Negative effects

• Coral bleaching

  • Increasing ocean temperatures cause corals to expel the algae living within them, leading to a loss of color and vitality, potentially causing coral death and disrupting entire reef ecosystems

• Ocean acidification

  • Absorption of excess carbon dioxide from the atmosphere makes the ocean more acidic, impacting marine organisms that build shells or skeletons, like oysters and coral, hindering their growth and survival

• Reduced oxygen levels

  • Warmer oceans can hold less dissolved oxygen, creating 'dead zones' where marine life cannot survive

• Food web disturbance

  • Changes in species distribution and abundance due to climate change can disrupt the balance of predator-prey relationships within marine ecosystems

• Species migration

  • As water temperatures change, marine species may migrate to new areas to find suitable conditions, potentially altering ecosystem dynamics and disrupting food web

    • Cod and pollock have already moved further north to cooler water, but this has disrupted the ecosystem they have moved into

Climate change & atmospheric circulation

• The winds generated by the global atmospheric circulation transport heat throughout the Earth

• Changes in temperature may impact the Hadley cells and shift the subtropical high-pressure zones polewards

• This shift would:

  • expand arid regions

  • impact weather patterns in mid-latitude regions

  • intensify tropical cyclones

  • alter precipitation patterns by

    • increasing droughts

    • changing monsoon season

    • increasing precipitation

• Arctic warming may weaken and make the jet stream more unpredictable by reducing the temperature differential between polar and equatorial regions.

• These changes may result in prolonged extreme weather events like heatwaves and cold snaps

Climate change & ocean currents

• The ocean conveyor belt carries heat throughout the world

• Melting ice caps and glaciers increase the freshwater input into oceans

• This disrupts normal currents and the thermohaline circulation pattern, especially for coastal regions

• This circulation pattern relies on heavy salt water to transport water, carbon and heat around the globe

• Climate change has the potential of stalling or reversing the ocean circulation pattern

• Effects:

  • Altered weather patterns and local climates

  • Changes in marine and coastal ecosystems

  • Changes in fish migration and distribution affecting fisheries

• Example:

  • Slowing down of Atlantic Meridional Overturning Circulation (AMOC), which includes the Gulf Stream

  • This is leading to colder winters in Europe and warmer temperatures in the Arctic

Climate change & soil

• Climate change can affect soil through changes in temperature and rainfall, which can impact soil’s viability and potentially increase erosion

• Soil erosion reduces the fertility of the remaining soil

  • Soil erosion increases when rainfall is higher and vegetation is low

  • Warmer temperatures and increased rainfall increase soil loss on slopes

• Increased rates of drought

  • Slows plant growth

  • Reduces carbon cycling

  • Reduces nutrient transfer to the soil

    • The lack of nutrients and water exposes soil to erosion

    • Soil erosion can lead to desertification

• Agricultural practices expose soil to increased run-off and erosion

  • Overgrazing: grazing animals destroy vegetation that binds soil particles

  • Over-cultivation: soil becomes exhausted

  • Deforestation: loss of roots to bind the soil 

• Changing patterns of crop yields

  • Crop yields are estimated to reduce by over 20% as temperatures increase

    • Rice and soybean yields have already been smaller in all major production regions 

  • A changing pattern of rainfall will also threaten crop production

    • Too little rain and crops will fail

    • Too much rain and crops will rot in the fields

  • Suitable areas for agriculture will change

    • Farmers may have to change their crops 

    • Wheat grown in the USA will have to be grown in Canada

    • This would negatively affect the USA's economy while boosting Canada's

  • Coastal flooding may lead to salt intrusion

    which can reduce the availability of water for irrigation