What is climate change?

"Climate change refers to changes in the long-term climatic conditions of an area, and is a result of both natural phenomenon, such as volcanic eruption, and human-induced changes in the atmosphere, such as an increase in greenhouse gas emissions". 

There is growing consensus within the international scientific community that anthropogenic forces, e.g., land use changes, widespread deforestation and the burning of fossil fuels, contribute significantly to climate change.

Warming of the climate system is evidenced by increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea levels. Since 1850, when weather stations around the world began measuring temperature fluctuations, 1995-2005 rank among the twelve warmest years in the instrumental record of global surface temperatures. 

While temperature increases are widespread around the world, temperatures have risen faster over land areas than over oceans. 

Indications are that greenhouse gas emissions, especially Carbon Dioxide and methane, have increased and intensified over the past 20 years, and cities have played a key, though not yet fully understood, role in this process. 

This temperature increase has led to changes in global and regional climate patterns, which, in turn, have impacted the lives of local communities and economies. Projections indicate that a 2 degree Celsius  warming above preindustrial levels could result in permanent GDP reductions of 4%-5% in Africa and Southeast Asia.

“We shape our cities and our cities shape us.” 

Cities create two main impacts on the carbon cycle and climate system, i.e., land use changes and changes related to emissions of aerosols, greenhouse gases and solid waste. 

Cities also rely on inward flows of food, water and consumer goods that may result in emissions from areas outside the city. Affluence and lifestyle choices also determine emissions.

Historically, greenhouse gas emissions have been greater in developed than in developing countries, but this pattern is quickly changing with rapid urbanization in the developing world. 

China has recently overtaken the US as the world’s leading emitter of greenhouse gas emissions even though its per capita emissions are significantly lower (In 2005, Chinese emissions per capita was about 6 tons compared to 25 tons for the US). Together, the US and China emit about 35% of total greenhouse gases.

The responsibility for urban emissions is not distributed evenly throughout the urban population within and across countries. 

The city’s geography, i.e., the climatic situation, altitude and location in relation to natural resources and demographic composition (age structure and household size), affects consumption behavior, greenhouse gas emissions and the contribution of urban areas to climate change. 

More importantly, the way in which urban areas are managed affects their contribution to climate change.

Urban form and spatial organization (density) can have a range of implications for a city’s emissions. The high concentration of people and economic activities in cities can lead to economies of scale, proximity and agglomeration that reduce per capita emissions. 

Urban infrastructure and development policies lock in the physical and institutional contexts for the way people travel and live their lives, and influence lifestyle choices, which in turn impact urban emissions, e.g., a lack of efficient public transit and low parking prices in the city encourage greater car use.

The Kyoto Protocol identifies and regulates six major greenhouse gases, i.e., carbon dioxide, methane, nitrous oxide, hydro fluorocarbons, perfluorocarbon and sulphur hexaflouride. 

These are generated by anthropogenic activities, with energy supply responsible for about 26% of global emissions (mainly from the burning of fossil fuels), transportation about 13%, commercial and residential buildings 8%, waste 3%, industry 19%, and agriculture and forestry 31%. 

In other words, power generation for electricity, heat and industrial activities, land use changes, such as deforestation and burning, industry, agriculture, including fertilizer use and livestock, and transportation, such as fossil fuel for automobiles, are important sources of emissions.