The human race has relied on the planet's natural resources to drive growth in population and the economic development of this population. As a result, historically carbon dioxide emissions and economic growth have been linked. Through using natural resources to support economic growth and development, we have changed the balance between the earth's systems in ways which are, and will continue to, impact climate. This has primarily been through the release of carbon from the land system (where it is trapped as rocks or in hydrocarbons such as oil or is present in vegetation) to the atmospheric system in order to generate energy for use in electricity, heat and transport. As humans have increasingly interacted with their environment through resource use, they have introduced new flows of carbon between stores, and have acted to accelerate existing natural flows. The graph below shows increases in the carbon dioxide concentration in the atmosphere since the mid 1900s, as measured a Mount Loa, Hawaii.
Anthropogenic greenhouse effect
The greenhouse effect is a natural process by which a significant proportion of the sun's radiation that reaches the earth is absorbed by the land, seas and atmosphere. This is shown in the diagram below. Releasing carbon based greenhouse gases into the atmosphere increases the capacity of the atmosphere to absorb radiation, resulting in more absorption and warming. This accelerated natural process is termed the anthropogenic greenhouse effect.
Tradgedy of the Commons
Antropogenic (man made) climate change is an example of the tragedy of the commons. This concept first became widely know following an article written by Garrett Hardin in 1968 relating to the over-grazing of common land. This theory describes how, if multiple parties have free access to a common resource, the resource will be exploited and depleted. This occurs due to individuals maximising their own self-interest in the short-term, rather than focussing on more sustainable use that maintains the availability and quality of the resource for a common good over a longer time frames. Because it has not historically cost individuals anything to release carbon into the atmosphere, development and economic growth have occured at the expense of the environment. In the case of climate change, this activity has resulted in driving climate change as well as making parts of the world more sensitive to any changes in climate. Elsewhere on this website (Link), we look at how attempts to put a price on carbon emissions is an attempt to 'price' carbon into decision making and break the tragedy of the commons.
What human activities cause climate change?
Energy Use
A significant release of carbon from land stores to atmospheric stores has been as a result of energy production. The chart below shows the energy flows for the UK, demonstrating how the core oil, gas and coal imputs are transformed and used across transport, heating and electricity in commercial, industrial and domestic situations. Fossil fuels, such as coal, are made up of ancient organic material containing carbon. This carbon is released to the atmosphere when coal is burnt, unlocking the carbon that was previously 'locked away'. Similarly, petrol used in vehicles is derived from oil, which contains carbon from plants and animals that have decayed over millions of years. The combustion of petrol in engines releases this carbon back into the atmosphere.
Changes in the earth's surface as a result of human activity has also contributed to climate change. It has done this by: (i) releasing carbon trapped in vegetation and soils into the atmosphere when these materials are removed, as occurs in deforestation; (ii) limiting the biological pump that photosynthesis in plants and trees provides, which draws carbon out of the atmosphere into organic stores on land; and (iii) making areas more sensitive to changes in climate. This is explored in more detail here.
Waste Management
The processing and disposal of waste products can release significant volumes of greenhouse gases into the atmosphere. For example, landfills remain a common disposal route in the developed and developing worlds. Within landfills, the decomposition of organic material in wastes (for example food wastes) in the absence of oxygen causes the release of methane. This is a highly potent greenhouse gas. Waste management and the climate is explored in more detail here.
Impacts
Additional carbon in the atmosphere, present in greenhouse gases such as carbon dioxide and methane, increases the atmosphere's absorption of heat, causing increases in the temperature. The graph below shows the average global surface temperature anomaly (against 1961 - 90 averages) since 1850, based on data from the Met Office.
