Average global surface temperatures are increasing rapidly and causing a range of problems. This warming is due the ‘greenhouse effect’ caused by certain gases that trap heat in the atmosphere. The warming has different effects in different places, but all involve climate change.
Independent teams of scientists from all over the world have gathered conclusive evidence that shows the earth as a whole is warming up and that this warming is accelerating. The first five years of the 21st century, along with 1998, were the hottest on record.
Scientists have examined over a hundred years of temperature records and have shown that the average surface air temperature of the earth has risen close to 1°C over the last century. In some parts of the world, such as in the Arctic, Antarctic and northern Australia, the temperature rise has been more than this. On the other hand, some parts of the earth have actually cooled a little, such as over the south Atlantic and south Indian Oceans. Hence the term “climate change” is a more accurate descriptor of what is happening to our planet as opposed to “global warming”.
The forecasting models developed by climate change scientists show that parts of the earth will experience increased flooding and droughts, heat waves will become more frequent and severe, major sea level rises are likely, and there will be more hurricanes and typhoons.
Climate change is already causing a profound impact on human and ecological processes on the earth and the effects are set to accelerate. Regionally the effects are quite complex, with some parts of the earth getting hotter and drier, some a little cooler and wetter, and some regions more affected than others.
Most glaciers around the world are already retreating dramatically. For example, Montana’s Glacier National Park is predicted to lose its glaciers by 2030. The glaciers atop Mount Jaya on the Indonesian Island of Irian Jaya now cover only about 20% of the area they did in 1950.
The late summer coverage of the Arctic Sea ice is now more than 20% less than what it was in the 1970s and the average thickness of the Arctic sea ice in summer is nearly half of what it was 60 years ago. Later in this century it is expected that the Arctic ice will disappear entirely each summer and that shipping and fishing will take place in areas formerly inaccessible.
Average temperatures of the Antarctic Peninsula have increased by around 2.5°C since the 1950s and parts of the ice shelf in this region show clear signs of collapse.
In some regions, the growing season for crops is more than two weeks longer than it was in the 1950s. Many species of animals and plants are extending their ranges into higher latitudes. For example, the boreal forests of North America are commencing a large-scale shift northwards as the tundra thaws. Parasitic diseases are becoming more widespread. For example, the ranges of several species of disease-spreading mosquitoes are spreading outwards from the tropics and making inroads into temperate regions. In 2002 during a record heat wave, mosquitoes carrying the West Nile virus spread across the United States and into Canada causing more than 850 deaths.
Climate change is being caused by humans artificially adding huge amounts of greenhouse gases, particularly carbon dioxide, into the atmosphere – much more than would be released from natural processes such as decay of organic material and the respiration of animals. This started about 150 years ago when humans began to burn large quantities of fossil fuels such as coal, oil and gas, for their energy needs.
Fossil fuels are used for the production of electricity, to run our cars and trucks and airplanes, to heat homes and buildings and for cooking and other uses. In the centuries before the Industrial Revolution, atmospheric levels of carbon dioxide were around 280 ppm (that is 280 molecules of carbon dioxide for every million molecules in the air). Atmospheric levels are now at 380 ppm – a 35% increase.
The amount of carbon dioxide humans are now releasing into the atmosphere is staggeringly huge – each year humans belch about 27 billion tonnes of carbon dioxide into the atmosphere, and this is increasing by 1% a year (for comparison, about 15 billion tonnes was released in 1970). One tonne of carbon dioxide is an amount that would fill all the rooms in an average New Zealand house.
Much more carbon dioxide is now being released into the atmosphere than can be reabsorbed by plants and the oceans. Of this 27 billion tonnes, 7 billion are absorbed by the oceans, 7 billion are taken up by forests and crops as part of the photosynthetic process, while 13 billion accumulate in the atmosphere. In the past few years, however, carbon dioxide is accumulating much faster in the atmosphere – from an average of 13 billion to 18 billion tonnes. This seems to be the result of a decreasing ability of the oceans and forests to absorb as much carbon dioxide as they once did in the face of rising temperatures and increasing carbon dioxide concentrations.
How greenhouse gases cause climate change
Carbon dioxide (CO2) is one of several greenhouse gases responsible for climate change. Carbon dioxide is the most important in causing the overall greenhouse effect. Methane is the next in importance. Methane originates mainly from rice paddies and from the digestive processes of livestock such as cattle and sheep. Although there is much less methane in the atmosphere compared to carbon dioxide (1.8 ppm as opposed to 380 ppm) methane is a much more powerful greenhouse gas. Ozone (O3), nitrous oxide (N2O), and chlorofluorocarbons (CFCs) are the other chief greenhouse gases. Ozone forms when sunlight reacts with pollutants in the atmosphere; nitrous oxide comes from livestock and fertiliser use; CFCs are found in spray cans and air conditioners and refrigerators.
Because greenhouse gases are composed of molecules with three or more atoms (as opposed to oxygen (O2) and nitrogen (N2) the main gases in the atmosphere which are molecules with 2 atoms), they are better at absorbing heat radiating from the surface of the earth and preventing much of this heat from escaping into space. This results in a warmer atmosphere. As more greenhouse gases accumulate in the atmosphere, the warming effect accelerates.
The various greenhouse gases vary widely in their ability to cause climate change. Climate change scientists often use a unit called the “global warming potential” to measure the power of a greenhouse gas to cause climate change. The global warming potential is related to the potency of a gas to trap heat in the atmosphere and its lifespan in the atmosphere compared to carbon dioxide. For example, methane traps heat much better than carbon dioxide but is shorter-lived than carbon dioxide in the atmosphere. Methane’s global warming potential is thus around 23 compared to 1 for carbon dioxide. In practice when scientists want to measure the total amount of greenhouse gases being emitted into the atmosphere they multiply the global warming potential of each greenhouse gas by its concentration to produce a total measure called the carbon dioxide equivalent (CO2e) which is a measure of these gases as a group.
What needs to be done
At the present rate of increase, the amount of greenhouse gases in the atmosphere will roughly double by the mid- to late 21st century. Climate change scientists predict that this will result in warming of the planet of somewhere between 1.5 and 6.5°C, with the most likely outcome between 3 and 4°C. The majority of climate change scientists believe that a rise of 3°C or more could tip the planet into run away climate change, triggering complete melting of the Greenland ice sheet, extensive melting of Antarctica, huge rises in sea level, and large changes to oceanic circulation – in short climate and human chaos.
There is thus a consensus among climate change scientists and environmental groups that we must stabilise the climate at 2°C above pre-industrial levels to avoid likely catastrophic events.
This will be very difficult to achieve and requires that major cuts in greenhouse gas emissions take place over the next 20 years. It is estimated that global emissions will need to level out and begin dropping by 2015 and that all developed countries will need to have reduced emissions by 15 – 30% below 1990 levels by 2020 in order to have a 60% chance of stabilising climate change at the the 2°C level. Any delay in cutting emissions to these levels makes the target almost impossible to achieve. For example, if the developed countries continue to emit as they are after 2012 then it will prove impossible to reach the 2°C target by 2030.
So, the bottom line is, if we are going to have any chance of heading off extreme climate change, and the resulting human and environmental chaos it will cause, by mid-century we all have to take immediate steps to significantly reduce our greenhouse gas emissions. This will affect us in profound ways including how we produce our energy to power our homes, businesses and industries, how we use energy in our homes and businesses, the ways we get from one place to another, how we make and recycle our consumer goods, and how we grow crops, raise livestock and manage our forests.
In 2004 New Zealand emitted about 75 million tonnes CO2e of greenhouse gases. In comparison, in1990, New Zealand emitted about 62 million tonnes, so our greenhouse gas footprint is increasing rapidly.
New Zealand is unusual amongst developed nations in that more than half of our total greenhouse gas emissions come from agriculture, mainly methane from livestock and nitrous oxide from animal waste and fertiliser use. Emissions from agriculture typically make up about 12% of greenhouse gas emissions in most other developed nations.
Agricultural emissions are up about 15% from 1990. Emissions from the energy sector (electricity generation and transport) have increased about 34% relative to 1990. About two thirds of New Zealand’s electricity production comes from hydro power, but there has been an increasing proportion of fossil fuelled electricity generation from gas and coal. This means that electricity sector emissions are growing at a rapid rate.
On a per person basis, New Zealand is a major emitter of greenhouse gases. Australia and the United States lead the world with per capita emissions of about 25 tonnes of carbon dioxide equivalent. Canada is next at 23 tonnes and then New Zealand at about 21 tonnes.