The Earth’s climate changes continually, but what is referred to as climate change or global warming is a set of dramatic changes that have been primarily caused by human activity since the beginning of the Industrial revolution.
This period has seen a major increase in the concentration of atmospheric ‘greenhouse gases’. These gases have, over eons, acted as a kind of barrier helping to retain heat in the atmosphere, but in modern times their increased concentration is raising temperatures to dangerous levels.
In recent times almost every year brings record temperature increases. Average global temperatures are now about 0.8˚C above pre-industrial times and rising. This may not seem a lot, but the consequences, outlined below, will be devastating if we do not curb this increase.
The following are the main greenhouse gases emitted as a result of human activity:
- Carbon dioxide, the most important such gas, is generated by the burning of fossil fuels, land clearing, the burning and decay of organic matter, and the production of cement.
- Methane, the second most important greenhouse gas, is more potent than carbon dioxide but there’s less of it. Human-generated sources of methane currently account for about 70 percent of its annual total, and these include livestock (especially cattle and sheep) farming, rice growing, the burning of coal, natural gas and biomass, and decomposition in landfills.
- Surface-level ozone, primarily caused by photochemical smog.
- Other trace gases caused by industrial activity, such as nitrous oxide and fluorinated gases (or halocarbons).
Water vapour is the major greenhouse gas, but it is not in the main generated directly by humans. However, the amount of water vapour in the atmosphere increases as air temperature rises, and so this increase can be said to be indirectly caused by human activity.
What are the consequences of climate change?
Climate change will affect (and in many cases is already affecting) Australia in a number of significant ways, including through:
- Rising temperatures
- Increased bushfire risk
- More frequent and/or severe rainfall, drought and other extreme weather events
- Sea-level rise causing coastal flooding and erosion
- The destruction of the Great Barrier Reef
- Increased risk of tropical diseases as climatic zones move south.
These will cause deaths from heat stress, bushfires, floods, storms and probably disease, greatly reduce food production, and seriously undermine our quality of life.
Globally, the same factors will bring about the same results, but billions of more impoverished people worldwide will be more severely affected by declining food production, rising sea levels, storms, floods, disease and other effects of climate change.
A particularly ominous threat is posed by what are called positive feedback loops. For example, as Arctic ice melts, less heat is reflected off light coloured ice back out into space, and more of this heat is absorbed by the earth’s surface, causing high temperatures and more ice to melt, and thus the process reinforces itself. Other examples of this phenomenon involve thawing permafrost, increasing water vapour, drying rainforests and bushfires. The danger is that, as these positive feedback loops develop momentum, they may spiral out of control and eliminate any possibility of humans halting or reversing the process.
How do we know climate change is happening?
Ninety-seven percent of scientists researching climate change believe that it is being caused by humans. There conclusions are based on a huge volume of data collected over many years, drawn, for example, from ice core samples, tree rings, marine sediment and other data sources that provide information about the atmosphere from up to 800,000 years ago, as well as on data concerning more recent air and sea temperatures, rain and snowfall, sea levels, ocean salinity and acidity, ice cover and much more.
This consensus is supported by the world’s leading scientific and research institutions.
Unfortunately climate data collected in the past few decades has shown that the degree of change that has actually occurred has tended to be at the upper limit of predictions based on climate change modelling. In other words, the climate has been changing faster than expected.
Why is action so urgent?
There is a lag of several decades between the time when greenhouses gases are emitted and the time when they raise atmospheric temperatures and generate all the adverse effects just described. This is because the world’s oceans initially absorb most of the heat increases. Thus the causes of the signs of climate change we are now witnessing go back decades, and the actions we are taking today will have irrevocable consequences decades hence.
Is it all bad news?
The picture outlined here looks pretty grim, but there are substantial grounds for hope. We are in the middle of a renewable energy and energy storage revolution that is spreading across the globe, with new products hitting the market frequently and prices tumbling. Renewables have reached price parity with fossil fuels and are in the process of getting much cheaper. The energy efficiency of materials and equipment is constantly improving. Twenty-first century public transport systems are springing up in cities and regions across the globe, while private car use is declining in the US and in every Australian capital on a per capita basis. Zero carbon buildings and precincts will before long become zero carbon cities. In 2015, for the first time in 10 years, global carbon emissions stopped growing. In every area of life in which our actions have contributing to climate change we now have the technology and the knowledge to do things differently – from agriculture to housing, forestry to transport, office buildings to manufacturing.
We know that we can live a low and before long a zero carbon life while continuing to enhance our wellbeing. Governments are starting to come together. Citizens are mobilising. We just need to keep applying ourselves to the task with greater speed. We have no alternative. The signs of hope are clear in this article, and in this one.
What about population growth?
One last issue to mention. Many people fear that global population growth is spiralling out of control and threatening not only the climate but the entire material basis of our wellbeing and survival. But studies challenge this. According to the World Bank we have recently been experiencing the most rapid decline in population growth ever, heading to 1% by 2020 and to less than 0.5% in 2050 (from an all-time high of over 2% in 1968). It’s predicted to peak at around 9 billion some time next century and then to decline slightly.
Experience shows that the best way to reduce population growth – in fact the only way outside of highly authoritarian societies – is to meet the basic needs of all the population, and in particular to ensure that women and girls have access to education and women can control their fertility. If these things occur people almost always choose to have smaller families. And these preconditions are occurring, as poverty the world over has declined dramatically (as this amazing video shows). It should also be remembered that it’s not just how many people there are, but the greenhouse emissions and resource use of each person, so these need to be reduced while maintaining prosperity.
Here are some more facts about climate change from an authoritative source: