Climate change

Long-term records of the Earth’s weather patterns show an increase in temperatures on all continents and across all oceans. These can have a potentially disastrous effect.

Climate is the average weather pattern of a region over a long period. It includes the variations in temperatures, and the frequency and intensity of wind, rain and drought. 

The climate of the Earth has always been changing. For millions of years, the planet has been varying in regular cycles between ice ages and warmer interglacial periods like the one we live in today. Even from year to year there can be major variations, which is why it’s important to look at long-term averages to identify trends. 

Global temperature records go back about 160 years, providing an accurate picture of the recent past. [visualise] They show us that average global surface temperatures have risen by about 0.74ºC since the start of the twentieth century. The increases have been measured on all continents, and in the oceans. It’s clear. The earth is getting warmer.

Today, average global temperatures are measured by three institutions: one in the UK (the Hadley Centre Climatic Research Unit at the University of East Anglia), and two in the US (Goddard Institute for Space Studies and National Climatic Data Center). Each centre works independently and uses different methods to collect and process data from around the world. However, their results are very similar. All three agree that warming of the globe is occurring, and has been particularly rapid since the 1970s. In fact, the last decade was the warmest on record. 

Even small variations in climate can alter environments dramatically. For example, there is just a 3-5°C difference between the average global temperature of today and that of the last major ice age. 

The term ‘climate change’ refers to the significant effects of this warming, which in addition to rising temperatures include increasing risk of droughts and floods, storms of greater intensity, and higher sea levels. 

The Earth’s climate is naturally subject to temperature variations. However, the science indicates that human activities have contributed to a recent growth in greenhouse gases like carbon dioxide (CO₂) in our atmosphere, and the subsequent rise in temperature.

The Earth’s climate system is powered by energy from the Sun. There are a number of factors that can alter the energy balance, including changes in the Earth’s orbit around the Sun, major volcanic eruptions, and variations in the composition of the Earth’s atmosphere. When one or more of these happen, significant changes in the Earth’s climate can occur. 

The Earth’s atmosphere consists of 99% nitrogen and oxygen. [visualise] These play no role in maintaining the planet’s temperature. However, the other 1% of the atmosphere includes gases that trap the sun's energy, contributing to rising surface temperatures. These are commonly referred to as ‘greenhouse gases’. Naturally occurring greenhouse gases include water vapour, carbon dioxide, methane, and nitrous oxide. The most significant greenhouse gas is carbon dioxide, also known as CO₂.

Carbon dioxide represents up to 77% of total greenhouse gas emissions.  By studying air bubbles trapped in ice-core samples from the Antarctic, scientists know that the concentration of CO₂ in the atmosphere was stable at between 180-300 parts per million (ppm) for the past 650,000 years. Since the Industrial Revolution, however, levels have risen to 389 ppm in 2010. [visualise] In the southern hemisphere, the CO₂ levels do not differ significantly. [visualise] Concentrations of other greenhouse gases in the atmosphere have also risen dramatically since industrialisation.

Scientists use computer simulations or ‘climate models’ to predict future climate changes and explain past climate changes. It is only when ‘anthropogenic’ (that is, human-generated, or man-made) greenhouse gas emissions are included in their computer simulations can the observed increased rate of atmospheric warming be explained [PDF].

So not only does the overwhelming body of peer-reviewed scientific evidence show that climate change is happening – it also shows that the rapid increases in greenhouse gases which are causing global warming are almost certainly due to human activities.

Examples of human activities that emit greenhouse gases like CO₂, and thereby contribute to global warming, include: intensive agriculture, land clearing, and the burning of fossil fuels like coal, oil and natural gas. [visualise]

There is widespread agreement amongst climatologists that if we continue to emit greenhouse gases at the current rate, then temperatures will continue to rise, resulting in even greater impacts on the Earth’s climate.

There is widespread acceptance among the global scientific community that the Earth’s climate is undergoing a pronounced period of warming, and that human-induced greenhouse gas emissions are the primary cause.  

The world’s leading scientific body on climate change is the Intergovernmental Panel on Climate Change (IPCC). It was established by the United Nations Environment Programme and the World Meteorological Organization (WMO) to “provide the world with a clear scientific view on the current state of climate change and its potential environmental and socio-economic consequences.”

The IPCC reviews the research from thousands of scientists studying climate across the world. It compiles reports to summarise the current understanding of climate change science. The most recent, The Fourth Assessment Report, was published in 2007.

The IPCC Fourth Assessment Report states that: “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level…. Most of the observed increase in global average temperatures since the mid-20th century is very likely [meaning more than 90% certainty] due to the observed increase in anthropogenic greenhouse gas concentrations.” [PDF] 

The conclusions of the IPCC have been endorsed by dozens of scientific bodies around the world, including The Royal Society of the UK, the NASA Goddard institute of Space Studies, and the National Oceanic and Atmospheric Administration. No scientific body of national or international standing is known to reject its basic findings of human influence on recent climate change.

The National Academies of Science from 19 different countries, including the US, Australia, the UK and China, also endorse the consensus. In a joint signed statement 11 National Academies have called climate change “real” and called for urgent action by governments to reduce greenhouse gas emissions. [PDF]

In 2004, a study surveyed 928 abstracts or ‘summaries’ of papers from scientific journals over a ten-year period form 1993 to 2003 that contained the keywords “global climate change”. None of them disagreed with anthropogenic climate change. 75% explicitly or implicitly agreed, 25% were methodological or took no position. 

A poll of 3,146 scientists in 2009 found that 82% answered “yes” to the question: "Do you think human activity is a significant contributing factor in changing mean global temperatures?” The survey included 77 climatologists actively engaged in research, of whom 75 answered “yes.” [PDF]

It is clear that there is widespread scientific acceptance that human activities are influencing Earth’s climate. Uncertainty is not a valid excuse for delay in reducing greenhouse gas emissions.

As the driest inhabited continent on earth, Australia is particularly vulnerable to the effects of climate change. 

Average annual temperatures in Australia have increased by about 0.9°C since 1950. According to the Australian Bureau of Meteorology, 2009 was the second warmest year in Australia since records began in 1910 and the decade 2000-2009 was the warmest decade on record. [visualise] Scientists warn that we can expect these patterns of warming to continue, with Australian average temperatures rising 0.6-1.5°C by 2030, and 1-5°C by 2070, depending on future levels of greenhouse gas emissions.

In 2007, the Australian Government commissioned an independent research report to examine the impacts, challenges and opportunities of climate change for Australia. In its final report, the Garnaut Climate Change Review summarised its assessment of a future with no reduction in the production of greenhouse gases: “Growth in emissions is expected to have a severe and costly impact on agriculture, infrastructure, biodiversity and ecosystems in Australia.”

There is likely to be less rainfall and more droughts in the south, uncertain rainfall changes in the north, more heat waves, less snow, and more frequent and intense bushfires and storms.

A particularly critical area for the nation in terms of environmental impact is the Murray Darling Basin. Stretching across one million square kilometres, the area is responsible for more than 40% of the value of Australia’s annual agricultural production. This includes dairy, fruit, vegetables, and grains. If there is no mitigation in greenhouse gases and global warming continues at predicted rates, it’s estimated that decreasing water runoff in the Basin will result in agricultural production falling by 12% by 2030, 49% by 2050, and 92% by 2100. [PDF] This will impact not only on domestic consumption, but also on export revenue.

As well as threatening Australia’s food production and water supplies, climate change is likely to affect the biodiversity of some of Australia’s iconic regions, such as the Great Barrier Reef and Kakadu’s wetlands, and the tourism economies they sustain.

Predicted rises in sea levels will have serious impacts not only on our coastal areas, but also those of our near neighbours in low-lying Asian cities and the Pacific Islands, possibly resulting in increased geopolitical instability.  

Scientists and economists generally agree that responding to the challenge of climate change will not be easy or inexpensive. Indeed, the Garnaut Climate Change Review concluded that the costs of climate change for Australia will be relatively greater than for other developed countries. However, if we continue to delay in our action, the costs could climb even higher. Worse, they could create a crippling burden not only on our generation, but generations to come. 

We are already seeing the effects of climate change. Unless we take action to reduce global warming, the worldwide negative impacts could be dramatic.

Because of the greenhouse gases already in the atmosphere, and the current rate of emissions, a rise in average global temperatures of 0.8 to 1.5 ºC by 2030 is likely to be unavoidable. 

Already, both the Greenland and Antarctic ice sheets are losing mass and contributing to sea level rise at an increasing rate. The area of summer sea ice remaining during the period of 2007 to 2009 was about 40% less than the average projection made by IPCC in its 2007 Fourth Assessment Report.

Future climate change will depend on the level of additional greenhouse gas emissions. If emissions continue unabated, the IPCC predicts that warming will continue at an accelerating rate. Global average temperatures could rise as much as 7°C by the end of the century. A temperature rise of this scale would have dramatic consequences for the Earth’s climate, including further declines in sea ice, glaciers, and snow cover, and more frequent and intense weather events such as heat waves, heavy rainfall and cyclones.  

The IPCC Fourth Assessment report estimated a potential sea level rise of 18 - 59 cm by 2100, but admitted that this was an underestimate, as they could not fully include contributions from melting sea ice and glaciers due to some uncertainties. Recent studies say sea levels could rise by as much as 1 to 2 metres by the end of the century in a high emission scenario. 

Melting glaciers could initially increase flood risk and then strongly reduce water supplies, eventually threatening one-sixth of the world’s population, predominantly in low-lying regions such as the Indian sub-continent, parts of China, and the Andes in South America. [PDF] Delicate ecosystems would be dramatically affected. 

A study by the Hadley Centre predicts that the proportion of land area experiencing severe droughts at any one time will increase from around 10 percent today to 40 percent for a warming of 3 to 4 degrees Celsius. 

The effects will be felt most in the developing world, and by those who are most vulnerable and lack the means to adapt to climate change. A warmer world is likely to intensify the existing challenges of these regions, such as dealing with shortages of food and water. The International Food Policy Research Institute estimates that 25 million more children will be malnourished in 2050 due to the impact of climate change on global agriculture.

Climate change will also result in increased geopolitical instability. According to one estimate, by 2050, some 200 million people may become permanently displaced due to rising sea levels, heavier floods, and more intense droughts. [PDF]

It also impacts on the economy. Former World Bank Chief Economist Nicholas Stern was commissioned by the British Government to examine how global warming may impact on the world economy. In his influential report released in 2006 he concluded that the costs of doing nothing would be far greater than the costs of early and decisive action to reduce greenhouse gas emissions and minimise the impacts of climate change. The costs of climate change could be 5% of global GDP in the future, even as much as 20% in the worst-case scenarios. In contrast, the costs of action to reduce our emissions could be limited to around 1% of global GDP each year.

We must act by making dramatic reductions in global greenhouse gas emissions.

The sooner we act, and the greater the cuts we make, the more likely it is that we will avoid the worst impacts of changes in climate.

The reality is that some further warming and changes in climate are now unavoidable, even if we were to stabilise greenhouse gas emissions today. But scientists say it is not too late to mitigate (that is, prevent the worst effects of) climate change. 

The International Energy Agency estimates that under current global policies [PDF] and emission trends we are on track to reach an atmospheric concentration of 1000 parts per million (ppm) of CO₂ and a rise of global average temperatures of up to 6°C by the end of the century. As the IPCC has warned, this variation in temperature would have dramatic and widespread impacts on the earth’s climate. It is clear that strong limits must be set on global warming.

That is where the 2°C limit comes in. Some scientists and governments have set a target of keeping the rise in average global temperatures to 2°C above pre-industrial times. It is believed that by limiting the warming to this level, the world can avoid some of the worst and more widespread effects of climate change. 

To achieve this goal, some scientists say that we must limit CO₂ concentrations in the atmosphere to 450 ppm. As a comparison, levels were at 385 ppm in 2008.

This makes it sound like keeping to 450ppm would be simple. However, think of these complicating factors: the world population continues to grow and is predicted to surpass 9 billion by 2050. As populations grow - and big countries like China and India urbanise and modernise - so does the demand for energy. By 2050, the world will be using more than double the amount of energy that it does today. There will be a significant and growing reliance on fossil fuels - particularly coal and gas - to provide the energy our ever-growing and developing world needs.

To stabilise atmospheric greenhouse gas emissions at 450 ppm and give us a reasonable chance of avoiding 2°C warming, global emissions of CO₂ must peak between 2015 and 2020. They cannot get any higher after that. In fact, they must rapidly decline to 50-85 percent below 2000 levels by 2050. 

So what does this mean? The fossil fuels we rely on now, and will continue to rely on, to provide us with cost-effective, secure energy also produce significant amounts of greenhouse gases. This means it is imperative that carbon capture and storage technology is rapidly developed and deployed on a massive scale. With carbon capture and storage technology, the world will get the energy it needs, while still mitigating emissions. 

But that is not the only answer. To make the necessary cuts in our CO₂ emissions, we must diversify our sources of energy, drawing more from renewable sources like wind and solar. Nuclear can play a role in a future global energy mix. The actions we take on an individual and collective level to reduce our energy consumption can make a big difference. Carbon emissions can be offset, by planting trees. In addition, there are new scientific and technological ideas being developed every day that can help. 

It is clear. There is no one “solution” to climate change. Instead, we must work together to invest in every possible answer. This approach has solid scientific backing. Two Princeton University economists, Robert Socolow and Stephen Pacala, have encapsulated the idea of "we must do everything" in their Wedges theory. The goal is to keep CO₂ emissions levels at approximately 2005 levels, while maintaining economic growth.

Socolow and Pacala highlight at least 6 different "stablisation wedges," which include "more efficient use of electricity," "increased use of renewables like wind" and CCS. [PDF]

Similarly, the International Energy Agency illustrates the wedges approach and the various contributions from each stabilisation wedge in reducing global CO₂ emissions from a business-as-usual baseline scenario. [visualise]

Taken individually, none of these actions can make a big enough difference to our atmosphere. But by investing in all of them, an advanced economy can stabilise its CO₂ emissions between now and 2050.