7.2 Climate Change - Causes
This subtopic contains a selection of slightly different angles on Climate Change. Students need to understand the difference between weather and climate, the difference between the greenhouse effect and the enhanced greenhouse effect, the greenhouse gases contributing to current climate change and the possible consequences of this climate change. There needs to be an understanding of how different locations may be impacted differently. Within this topic, students need to make links back to their understanding of feedback loops and, of course, tipping points.
Although not explicitly stated, it would be crazy not to expect students to understand which human activities are contributing to the contribution of greenhouse gases. These ideas also link strongly to subtopic 7.3.
Students also should be able to develop an appreciation of how different EVSs approach climate change and why this has led to so much debate on the topic when over 97% of climate scientists share a consensus on the human causes of climate change. Linked to this debate is an understanding of the role of climate models in making predictions.
On this page we are going to just focus on the causes.
- Climate change has been a normal feature of the Earth’s history, but human activity has contributed to recent changes.
- There has been significant debate about the causes of climate change.
- Climate change causes widespread and significant impacts on a global scale.
Recommended Teaching Time (not including practicals): 2 hours (Climate and causes)
From the Guide (IB ESS Guide 2015)
- Climate describes how the atmosphere behaves over relatively long periods of time, whereas weather describes the conditions in the atmosphere over a short period of time.
- Weather and climate are affected by oceanic and atmospheric circulatory systems.
- Human activities are increasing levels of greenhouse gases (GHGs, such as carbon dioxide, methane and water vapour) in the atmosphere, which leads to:
- an increase in the mean global temperature
- increased frequency and intensity of extreme weather events
- the potential for long-term changes in climate and weather patterns
- rise in sea level.
Checking Understanding: Are you ready?
1. Explain the difference between climate and weather.
2. Explain how oceanic and atmospheric circulatory systems affect both climate and weather.
3. Outline the major impacts of increasing levels of greenhouse gases, by humans, in the atmosphere.
4. Outline the potential impacts of climate change and how they could be perceived as positive or negative, including
a. water availability
b. distribution of biomes and crop growing
c. loss of biodiversity and ecosystem services
d. coastal inundation
e. ocean acidification
f. damage to human health
5. Discuss the feedback mechanisms that would be associated with a change in mean global temperature.
6. Explain how some of the feedback mechanisms can involve time lags.
7. Explain how the complexity and degrees of uncertainty affect the accuracy of climate model predictions.
8. Outline the debate surrounding climate change in contest of EVSs.
9. Evaluate contrasting viewpoints on the issue of climate change.
- Review the material on weather and climate, watching the videos from NASA and Bozeman Science. 7.2 Weather or Climate Review
- As a class or in groups try to draw a system diagram to illustrate the climate system. Click on the eye icon to see one I made with my class. The Climate as a System
- Explore the history of climate change using the HHMI interactive.
- Your challenge is to make a graphical representation of the factors that contribute to the increase in greenhouse gases in the atmosphere leading to climate change and ocean acidification. You will need to develop images that represent these factors - use a graphical language. 7.2 Causes of Climate Change
Weather vs Climate
Weather is the conditions is a given place at any one time. It is measured by the temperature, air pressure, precipitation (rain/snow etc.), wind speed, humidity. It will allow you to determine what to wear today! It is the conditions over a short period of time.
Climate is, if you like, the average of the weather over a relatively longer period of time, usually about 30 years of data is required to give the climate of an area. Climate patterns will determine the types of organisms which can survive and have adapted to live in a given area.
Weather and climate are both determined by the amount of solar radiation an area receives (latitude and the rotation of the earth on the its axis). You can say that solar radiation drives the climate system. If we think about climate as a system, would it be open or closed?
The amount of solar radiation (insolation) affects the circulation of the air above an area (see tri-cellular model of atmospheric circulation Sub-topic 2.4 Biomes, Zonation and Succession).
Movement of Matter
Air movement causes the redistribution of energy and matter, e.g. the Sahara dust which blows from Africa over the Mediterranean and acts as a fertilizer but also affects air quality in these areas.
Climate also includes the amount of precipitation that falls in an area and the temperatures over the course of a year (on average). This combines to create the biomes that you learn about in subtopic 2.4.
Climate interacts with ocean circulation and the proximity or distance from a large body of water (ocean) will affect the local climate. You learn about ocean circulation a little in sub-topic 4.1 where you understand that ocean circulation is affected by temperature and salinity and is ultimately also driven by solar radiation.
Areas near ocean currents can be warmed (e.g. the Gulf Stream and North Atlantic Drift across the Atlantic warms North-West Europe) or cooled (e.g. the Benguela current cools the South-East coast of Africa) by the ocean currents.
Proximity to oceans can also lead to fog deserts (S. America - Atacama in Chile) or increase the chances of thermal inversions (sub-topic 6.3 - San Francisco).
When mountains lie near to oceans there can be high precipitation on the ocean side of the mountains but desert conditions in the rain shadow of the mountains away from the ocean.
This video is a nice introduction to the differences between climate and weather. Stop the video at 2m 35s and answer the questions before moving on through the next 2 minutes of the video. See also this activity 7.2 Weather or Climate Review
For more on the links between weather, climate and the greenhouse effect watch this video:
The Greenhouse Effect
The greenhouse effect is a natural phenomenon whereby the earth's atmosphere re-radiates some energy back to the earth's surface, warming the atmosphere nearest the surface. This re-radiated energy is in the form of long wave radiation.
Greenhouse gases (GHGs) are what allow the earth to be habitable but human activities have contributed to an increase in GHGs. These include carbon dioxide, methane, water vapour and nitrous oxides. The IPCC does not include water vapour directly in its calculations as it is generally the result of the other GHGs' activities. The accumulation of these GHGs in the atmosphere traps more heat (infrared radiation) in the atmosphere and gives rise to increased average temperatures. This is known as the Enhanced Greenhouse Effect.
An Open or Closed System: Climate
- As a class or in groups, list the stores you would find inside the climate system.
- Identify the flows of energy and/or matter which enter and leave the climate system.
- Decide if you think the climate system is closed or open.
- Draw a system diagram to represent these stores and flows.
- Can you identify if they are transfers or transformations?
The Climate has always Changed
Use the interactive media on this HHMI resource to explore how the climate of the Earth has always changed. There are teacher and student resources to support the activity.
Human Activities Contribute to Greenhouse Gases
These increased GHGs are usually measured in carbon dioxide equivalent units as carbon dioxide has long been the major GHG. In the Fifth Assessment Report of the IPCC, published between 2013 and 2014, the contribution to GHG emissions between 1970 and 2010 was as follows:
- 59% CO2 from fossil fuel use and industrial processes
- 16% CO2 from forestry and land use change
- 18% from CH4 (methane)
- 7.4% from N20
- 0.81% from F-gases
What sort of human activities produce and release these GHGs - Drivers of Climate Change?
Human activities either directly release GHGs or change the way the land behaves, indirectly releasing GHGs, or changing the albedo of the land.
For more on albedo, see Modelling the Albedo Effect
Burning and production of fossil fuels
- power generation
- industrial processes such as metal refining, e.g. aluminium smelting, and cement production
- flaring of excess gas in oil production
- methane leaks from fracking and pipelines
Land Use Change
- Farming practices which emphasise inorganic fertiliser use
- Increased meat production
- simplifying ecosystems through landuse change
- melting permafrost releases methane
- urbanisation - imcreasing loss of land to the concrete jungle of cities
- paddy fields release methane
- animals produce methane in their guts
- heavy machinery running on fossil fuels
- farming practices which reduce soil carbon content
- inorganic nitrogen based fertiliser production and use - haber process is very heavily energy dependent
- halogenated gases used to replace the original CFCs which caused ozone depletion are strong GHGs