Climate Change part 3

Climate Change Causes

While there are likely some natural causes to the climate change we are experiencing today, the primary driver of the rapid climate change is the increased concentrations of greenhouse gases, particularly carbon dioxide, in the atmosphere.

Carbon dioxide concentrations are now at their highest level in the atmosphere in over 650,000 years, outweighing all other factors that contribute to climate change.

Orbital cycles, solar flares, volcanic activity, and other natural factors appear to account for less than 10% of observed changes of global temperature.

The global increase in greenhouse gases is overwhelming due to the action of people - through fossil fuel use and deforestation.

The table below explains some of the main sources of greenhouse gases, while the graphic above illustrates what sectors of our economy contribute most to increasing greenhouse gas concentrations in the atmosphere.

Greenhouse Gases	Industrial Sources	Land Use Sources
Carbon dioxide (CO2)	Fossil fuel combustion; Cement manufacturing	Deforestation; Burning of forests
Methane (CH4)	Landfills; Coal mining; Natural gas production	Conversion of wetlands; Rice paddies; Livestock production
Nitrous Oxide (N2O)	Fossil fuel combustion; Nitric acid production	Fertilizer use; Burning of biomass
Hydrofluorocarbons (HFCs) & Perfluorocarbons (PFCs)	Industrial processes; Manufacturing
Sulphur hexafluoride (SF6)	Electrical transmission; Distribution systems

The greenhouse gases emitted by all of these sectors accumulate in our atmosphere over time.

Before the industrial revolution, concentrations of CO2 were about 275 parts per million (ppm). Carbon dioxide emissions from human activities became a measurable factor in about 1850 and have been rising almost exponentially to today. Current emissions globally are about 30 billion tons of carbon dioxide equivalent (CO2e).

Some of the carbon dioxide that is emitted is absorbed by the oceans, by trees and grasses, or sequestered in soils, but more than half of the emissions stay in the atmosphere for long periods of time. Because of this, the concentration of greenhouse gases in the atmosphere has been increasing.

Today, the concentration of greenhouse gases in the atmosphere has reached 415 ppm CO2e and is rising at about 2 ppm per year.

It is this increasing concentration of greenhouse gases in the atmosphere that causes global warming.

There are a wide range of estimates for how high the concentrations of CO2 in the atmosphere will rise.

The graphic below illustrates IPCC estimates of future global greenhouse gas emissions.

These estimates predict a 25-90% increase in emissions in the absence of any additional climate policies.

The estimates vary because they are based on different assumptions about driving forces of emissions such as demographic development, socio-economic factors, and technological change.

Based on the emissions projections, temperatures could rise significantly, as shown in the graph above. Temperature increases across this range will have serious impacts on our planet.

More on this series:

Climate Change part 1 - What is climate change?

Climate Change part 2 (the greenhouse effect) - What is causing climate change?